SADCATS Preliminary Design Report - Rochester …edge.rit.edu/content/P04034/public/PDR.doc · Web viewSubmersible Autonomous Data Collection and Transmission System (S.A.D.C.A.T.S.)

REDESIGN OF ASUBMERSIBLE AUTONOMOUS DATA COLLECTION AND TRANSMISSION

SYSTEM(S.A.D.C.A.T.S.)

PRELIMINARY DESIGN REPORTDepartment of Mechanical EngineeringDepartment of Electrical EngineeringKate Gleason College of Engineering

Rochester Institute of Technology76 Lomb Memorial Drive

Rochester, NY 14623-5604

Design Team 3407 May, 2023Matthew RhoadsMatthew BuchwaldMatthew DeHavenJohn RobinsonDaniel RubinMatthew Stith

Executive SummaryThis report is a summation of the collaborative work produced by the persons defined within to achieve a reworking of a Submersible Autonomous Data Collection and Transmission System (SADCATS) for utilization in naturally formed bodies of water. The end product is intended to serve the needs of The Chester F. Carlson Center for Imaging Science as well as the Biology Department of The State University of New York College at Brockport. The goal is thus to design and fabricate a vessel that is capable of data collection in the scope of spectral irradiance, pressure, temperature and turbidity. Improvements have been achieved in the areas of data transmission, geo-location and weight. This year’s design also incorporates capabilities for directed surface locomotion which were not available on the original design.

The design process of this years design incorporates multiple facets of the Engineering Design Planner™ as developed by Dr. Edward Hensel, PE. To this date, the facets involving the concept development and paper design phase have been completed. These facets include recognition and quantification of the need, concept development, feasibility assessment, design and performance parameters, analysis and synthesis of design elements, and a report of the current status of the project, including a project outlook. Preliminary design documentation in the aspect of a technical data package has also reached fulfillment at this time.

Through this design process, the idea of the data collection submersible vessel evolved. The design decided on for the second generation of SADCATS will incorporate both surface navigation and static diving. A ballast system in the rear of the sub will be used to control diving via an air/water bladder. The vessel will only be capable of surface navigation by using two propellers mounted on the side of the vessel. These propellers will not only control forward propulsion but will also be used to change direction. The sensors that will be used include temperature, pressure, color, and turbidity along with a GPS module.

The technical data package portion of this report has been developed to incorporate relevant Computer Aided Design (CAD) documentation for the finalized design. Supplementing the CAD drawings, electrical flow diagrams and schematics of all relevant systems have been integrated into the package. All relevant computer coding and syntax has also been included for review as necessary.

Following the review of the Preliminary Design Report, the production and testing phase of the project will commence. The design will be fabricated, and assembled. It will then be calibrated and tested for conformity to the project sponsors specifications. After the relevant testing period has been completed, the finalized physical model will be delivered to the project sponsor for deployment and utilization.

document.doc 2 SADCATS

Table of ContentsExecutive Summary 2Table of Contents 3Table of Illustrations 51.0 Recognition and Quantification of the Need 6

1.1 Mission Statement 61.2 Definition of Involved Parties 61.3 Product Description 71.4 Scope of Limitations 71.5 Project Goals 81.6 Financial Parameters 81.7 Primary Market 11

1.8 Secondary Market Possibilities 112.0 Concept Development 12

2.1 Surface Vessel Concept 132.2 Solar Vessel Concept 14

2.3 Dynamic Submersible Concept 153.0 Feasibility Assessment 16

3.1 Surface Vessel Assessment 163.2 Solar Vessel Assessment 173.3 Dynamic Submersible Assessment 183.4 Resultant Concept from Feasibility Assessment 19

4.0 Design and Performance Parameters 234.1 Design Objectives 234.2 Performance Specifications 244.3 Design Practices Utilized 25

4.4 Safety Concerns 255.0 Analysis and Synthesis of Design Elements 26

5.1 Mechanical Design5.1.1 Hull5.1.2 Ballast System 5.1.3 Propulsion System5.1.4 Stability Control5.1.5 Component Mounting System

5.2 Electrical Design5.2.1 Microcontroller Selection and Design

5.2.1.1 Selection of Microcontroller5.2.1.2 Integration with Electrical System5.2.1.3 Organization of Program Structure

5.2.2 Power Electronics Board5.2.2.1 Diodes (Vishay, 1N5820)5.2.2.2 Power FETs (Motorola, IRF540)


5.2.3 Communications5.2.3.1 Modem and Radio Transceiver 5.2.3.2 Radio Amplifier, and Tx/Rx switch 5.2.3.3 GPS 5.2.3.4 Antenna5.2.3.5 Data flow, error detection and error correction5.2.3.6 Legal Restrictions

5.2.4 Data Acquisition and Sensory Package5.2.4.1 Pressure Sensor 5.2.4.2 Temperature Sensor 5.2.4.3 Turbidity/Conductivity Sensor 5.2.4.4 Color Sensor

5.2.5 Power Sources5.2.5.1 Selection of battery chemistry5.2.5.2 Determination of Battery Capacity/ Configuration5.2.5.3 Power Management5.2.5.4 Battery Voltage Sensing, Power Redundancy, Power Switching

5.2.6 Electromechanical Devices5.2.6.1 Motors5.2.6.2 Pump5.2.6.3 Solenoid Valve

5.3 Lighting5.4 Analytical Conclusion

6.0 Status and Outlook6.1 Obtainment of Components and Materials6.2 Fabrication 6.3 Testing and Calibration6.4 Budget 6.5 Project Completion Timeline

7.0 ConclusionReferencesAppendix


Table of IllustrationsA 15Table 5.2.1


1.0 Recognition and Quantification of the Need

1.1 Mission Statement

The Submersible Autonomous Data Collection and Transmission System Team is to design and fabricate a functional prototype to be delivered to the project sponsor for use in data collection. The prototype is to be a second generation offspring of the model produced during work conducted in the year prior. The model also is to be designed so as to not loose any of the functionality provided by the previous design.

1.2 Definition of Involved Parties

Project Sponsor:Dr. Robert KremensSenior Research ScientistChester F. Carlson Center for Imaging ScienceCollege of ScienceRochester Institute of Technology

Team Mentor:Dr. Wayne WalterTenured ProfessorMechanical EngineeringKate Gleason College of EngineeringRochester Institute of Technology

Project Group Leader:Matthew Rhoads BS ME

Project Group Members:Matthew Buchwald MS/BS EEMatthew DeHaven BS MEJohn Robinson BS MEDaniel Rubin BS MEMatthew Stith BS EE


1.3 Product Description

While significant resources have been allocated to research of the offshore regions within the Atlantic and Pacific Oceans; the quantity of data available from shallow lake research pales in comparison to the oceanic data available. Currently, data collection is carried out in a labor intensive manual fashion, often times via a bucket method, where specimens must be transported back to dry land for analysis. This tends to lead to issues of data inaccuracy resultant from contamination during transport, and the variation of environ between eco-system and laboratory. Thus it was proposed that an autonomous system be developed to aid in the acquisition and transmission of relevant data from the point of origin back to a base station for distribution and analysis.

The device in question was to be designed such that the capabilities of the first generation prototype are maintained. At the same time, improvements in communication, dry weight, geo-location capability, horizontal motion, and sensor feedback were to be realized.

Specifically, the project sponsor provided three scenarios under which the vessel could be deployed. The design team was informed that the project design could be made to address one of the scenarios, or to incorporate the means to be deployable in a multitude of situations.

Scenario:A. Surface Water Temperature Mapping

Water acts as an ideal blackbody emitter and therefore is a valuable calibration source for detectors of radiant flux. Thus Landsat, EO-1 and other satellites are calibrated using the lake. On an “overflight” day, GPS measurements and water surface temperatures are taken at about the time the satellite is overhead.

Consequently a surface vessel could be designed to relay position and temperature data to fixed station that serves up info on the web. A lifetime of two orbital passes, which typically takes 11-12


days, would be required. Inclusion of a measurement device for downwelled radiance, light that hits the surface of the water form all sources direct and reflected, was also desirable.

B. Submersible Data Acquisition

A device capable of taking temperature depth profiles, in Lake Ontario and Conesus Lake, to a depth of 20 to 30 meters was another possibility. GPS was to be utilized for positional feedback along with data collection telemetry and a radio transmitter to transfer the data to a base station. The data collection telemetry was to include temperature and turbidity as a function of depth and time. High time resolution is required at a rate of one measurement every minute, especially during rain events. The radio range was to be approximately 18 miles in radius about the base station located at RIT in Rochester)

C. Boats/Buoys with Full Directional Control

The ideal device was to measure surface temp, water color, brown/green/yellow, and downwelled light thus amounting to maybe 6 channels of data. Again GPS was to be utilized for positional accuracy, with radio range similar to that of Scenario B.

Throughout the design, for any or all missions, the most important features were to be:

Position awareness via GPS telemetry Mechanical design to suit the mission profile Cost effective design Simple design


1.4 Scope of Limitations

The SADCATS product design phase is to be completed by the conclusion of Fall Quarter (14 November, 2003) and is to include the following deliverables:

Preliminary Design Documentation Graphical Representation of the Elements Required to Construct

the Design Bill of Materials, Price Quotes, and Purchase Orders for Elements Design Presentation and Defense During Preliminary Design

Review

The SADCATS product fabrication and testing stage is to be completed by the conclusion of Winter Quarter (20 February, 2004) and is to include the following deliverables:

Working Physical Prototype Finalized Design Documentation Testing and Calibration Results Team Binder of Data Collected During the Design Phases

The SADCATS team members ARE NOT responsible for:

Deployment of the Prototype Development of Individual Components of the Design Component Integration rather than Fabrication Reception of Data at Base Station Relay of Data to Secondary Market Customers


1.5 Project Goals

The project will meet successful completion when the following facets have been met:

The project team members have developed the necessary skills to become an integral part of the multi-disciplinary engineering design process

The project team members have learned the appropriate analysis techniques as required by the design process

The final prototype product meets and or exceeds the goals and expectations imposed by both the project sponsor and the design team.

The final prototype has been completed within the budgeted time and financial allotments

The project’s results provide a basis for further development and or data acquisition.

1.6 Financial Parameters

The budget for the SADCATS project is tentatively set at $1000.00, and is to include:

Raw Materials Required for Vessel and Skeleton Construction Data Acquisition Sensors Lighting Elements Motor(s) Propeller(s) Pump Dive System Components Hydraulic Lines and Fittings Power Source(s) General Hardware


Electronic components are to be sourced first via the project sponsor.Specifically the sponsor is to provide:

GPS Unit Radio Communications Equipment Electronic Controller Hardware

The possibility for some limited fabrication of parts via the sponsor does exist.

1.7 Primary Market

The primary market sector for the SADCATS project is defined as the project sponsor. This consists primarily of Dr. Robert Kremens of the Imaging Science Center.

1.8 Secondary Market Possibilities

Secondary market possibilities exist in the provision of data acquired by the SADACATS device for use and interpretation by the following:

The State University of New York College at Brockport Calibration of Landsat, E0-1 and similar Satelites Other Parties interested in Research Data in Shallow Water Bodies


2.0Concept DevelopmentInitial concept development for the SADCATS design began with a

brainstorming session to bring to light possible solutions to the proposed topic areas inclusive to section 1.3 of this report. The brainstorming session produced a long list of twenty concept ideas which can be found in Appendix A.1. In order to obtain the greatest benefit from this initial concept development stage, no idea was left uncovered and every idea has been documented. Through group discussion and a team polling procedure, the long list was narrowed to the three concepts described below. While the three selected concepts contain distinct variances, all relevant original concept components have been retained. Due to the variability of the project statement by the sponsor, specific design concepts may be found to be inherently biased toward a given sector of project development.

Found hereafter, is an in depth description of the three top concepts. While not intended to actually represent the finished design product, they are meant to portray possible solutions to the above design criteria while maintaining the general physical properties consistent with products similar to the aforementioned conceptual models. Also included, the electrical block diagrams are intended to give a general feel for the integration and interaction of required components within the design envelope.


2.1 Surface Vessel Concept

The surface vessel concept arose directly from the concept reduction process. The main drive for a surface vessel capable of the required tasks was a reduction in complexity over that of a submersible vessel.

The design team thought that the surface vessel could be “overbuilt” to enable future modifications to make the vehicle a submersible. Creating extra space would also allow for further additions of sensing and communication technology.

The concept of the surface vessel incorporates two motors which extend outboard from the hull. The motors would be located away from the body of the vessel to ease turning. The motors would be configured to be under the water line to allow the propellers to have full contact with the water. A rudder was planned for the bottom of the vehicle to aid in vessel stability. The components of the surface vessel would be mounted in the center and near the bottom of the hull. The location of the internal components is critical to allow the vehicle to be upright in the water.

Since this is a vehicle that operates on the surface of the water, it would also have navigation lights designed to increase safety. Other boats must be able distinguish water from this vessel so they can avoid a collision. Since the vessel is small in size, and low speed, the most effective solution would incorporate a white light viewable 360 degrees around the vessel.


2.2 Solar Vessel Concept

During the initial design phase of the project, one of the main areas of interest was that of solar cell power. The idea mainly arose from the desire to have an active way to replenish and or increase the power capacity of the vessel. Thus the two main scenarios for operation were in that of a vessel obtaining all of its required power via solar means, and a vessel that would use to solar cells to recharge batteries that would in turn power the vessel.

In addition to the possibility of using solar cells, one group member suggested using a sail to provide some to all of the navigational power, thus allowing for the solar cells to only provide enough energy to power the data acquisition equipment.

As the solar vessel was mainly thought of as a surface going craft, the data acquisition and telemetry design would be similar to that of the electric surface vessel, and as such the vessel would be best suited to the Scenarios A and C of Section 1.3.

Electrically, the solar vessel would require the addition of the cells themselves, and a battery recharging board to regulate the replenishment of battery power. Mechanically, a device to orient the solar panels would also likely be needed.


2.3 Dynamic Submersible Concept

Keeping in tune with the development work conducted in the prior generation of SADCATS, the main concept was the development and construction of a submersing vessel. Thus the concept would be capable of meeting all of the scenarios of Section 1.3.

The initial submersible concept development looked at the inherent benefits of both open and closed frame designs. The main scope of the initial submersible was to contain dynamic motion capabilities both above surface and below, via a design that would be inherently productive in both scenarios. Said design would thus allow for a varying mission where data acquisition below surface could be obtained, as well as surface data.

The concept model looked to achieve navigational means on surface via GPS, and under surface via either inertial or magnetic means. Radio transmission of the data collected would be conducted during surface dwelling time only as the radio would not be capable of transmission while under water.

A ballasting system was to be incorporated either inboard or in connected outboard dive tanks. From an early stage, the possibility of using two externally mounted motor-propeller assemblies on opposite sides of the vessel was incorporated. Moveable control surfaces were discussed in an effort to aid in navigational capabilities. The submersible would carry a similar sensory package to that of the surface vessel, with the addition of pressure and turbidity sensors for use when submersed.


3.0Feasibility Assessment

3.1 Surface Vessel Assessment

Navigation was one of the primary concerns of the project. As such, it became a large part of the driving force behind designing a service vessel. Underwater navigation is difficult due to the presence of location control where as surface navigation provides a means for satellite communication via GPS. The GPS system used under last years design was found to be sufficient for all required mission parameters, and provides easy integration. The radio transmission capabilities for the surface vessel are also easily accomplishable, and again the equipment utilized in the prior generation could be incorporated.

The surface vessel would be able to take measurements of surface temperature, water color, and down-welled radiance. By the general nature of the design, the vessel would not be able to acquire information from water at depths greater than a foot or two under the surface without a deployable means of “dropping” sensors to greater depths.

To address the issue of underwater data collection, a tether was investigated as a way to have surface mobility while still maintaining the ability to take measurements of the water below. If the tether was long enough, it would be able to reach up the desired depth of 100 feet. However, there is no way to make sure the tether would drop straight down. The hanging tether also presents snagging hazard to the device. A hanging cable 100 feet long is bound to get stuck on something sooner or later. A built-in location error that is a result of the GPS system must also be considered. The combination of the errors would make for unreliable underwater data collection.


3.2 Solar Vessel Assessment

For the best efficiency, the solar panels would need to be angled toward sunlight. Thus the design of a mechanism to tilt the solar cells such their orientation would allow for the absorption of maximum sunlight would need to be incorporated. This in turn leads to additional complexity within the control system. If the vessel submerged, it would also complicate the dive systems due to the added mechanical parts. If the panels were fixed and not controlled to correct with sunlight, they would still require integration with the hull, which adds difficulty in the area of watertight design.

Due to the constant motion of the water’s surface, a tilt mechanism would likely not be able to maintain the proper angle, and the solar panels would therefore be subject to a somewhat random ability to receive solar radiation. It would be difficult if not impossible to ensure that the panels would even be angled towards the sun. As solar panels only absorb a certain range of wavelengths of electromagnetic radiation, they will not absorb all the available energy from a panel even when at maximum angle. This may be as low as 15% of the total possible power due to electromagnetic radiation.

Average yearly available sunlight for the Rochester area is roughly 50%, which determines that the panels will not always receive sufficient sunlight. As of 1990, the solar radiation in the area would yield roughly 2.5kWh/m² per day. As the panels that could be integrated within the vessel would be small in size, the power generated by the cells would be relatively low. The absence of sunlight on particularly cloudy days is unpredictable. Therefore even when on the surface, the vessel would not be guaranteed to receive sufficient power from the cells. In this case, the cells would merely be added weight, thus adding to the power required to propel the vessel through the water.


3.3 Dynamic Submersible Assessment

Due to the inherent properties of water as a medium of submersion, the first issue encountered in the analysis phase of the concept was that of underwater navigation. GPS signals are not able to be used in underwater environ due to the scattering of the signal as it hits the water’s surface. This led to research into the areas of inertial navigation and magnetic navigation.

On the topic of inertial navigation, it was determined that many ocean going research submersibles utilize pre-made inertial navigation systems. Unfortunately, these systems tend to be large in physical size. Smaller versions are available, but were found to be beyond they financial scope of the project at hand.

Another option in the realm of inertial navigation was that of creating a custom package using accelerometers purchased from an outside source, and utilizing a custom circuit. From the standpoint of cost and mechanical feasibility this was a viable option, but the programming for such a device was seen to be quite complex, and thus, due to limited project development time, this option was also surpassed.

Digital, steady-state magnetic devices are also available on the common market. Again research was conducted into pricing and integration into the overall design of the vessel. Unfortunately, due to the limited budget, and the complexity of the algorithm requited to process the data feedback from the device, magnetic navigation was ruled out.

While research was being conducted into the navigational control facet of the design, research was also conducted into the possibility of mobile control surfaces for underwater application. It was found that the sealing of any actuator rods and other linearly mobile items would be somewhat difficult.


From a ballast standpoint, the design team was limited only by imagination in the area of design. Both external and internal ballast tank systems were considered. The main drawback in many of the commonly applied systems was found to be an excessive dry weight. In looking at the previous generation SADCATS device, one soon finds that a good majority of the weight, and the reason for such a large vessel, is directly correlated to the issue of the scuba tank used to purge the ballast water from the ballast tanks.

Not only does the weight of the tank play into weight hindrance, but if one looks at the physical size of the tank, they find that volumetrically there is a large quantity of displacement, which creates a high buoyancy force that must be overcome in order to provide diving capability. Consequently, it was determined that the system must be both significantly lighter and much smaller in size than commercially available systems.

Lastly under consideration when building a submersible, is the issue of pressure vessel design. A main concern with the GPS module was the issue of metallic enclosure. Thus it was decided that at the least, the section of hull in which the GPS is located would have to be constructed of a non-metallic material. Investigation into the capabilities of in-house welding also proved that metallic construction was likely out of the question due to concerns for a water tight seal at pressure.

3.4 Resultant Concept from Feasibility Assessment

Further analysis was conducted to determine which of the above concepts would best meet the needs of the design project. A list of criteria that would be incorporated into the design was constructed. The listed consisted of weight, cost, reliability, adaptability, difficulty, part availability, life span, package, serviceability, communications, power consumption, and capability.

Definitions of Criteria:


Weight: total weight of deployable deviceCost: total cost of parts and man hours to put together deviceReliability: accuracy of dataAdaptability: ability to add more parts in the future, space for

expansion, easy to modifyDifficulty: will the group be able to build debug to intended design

functionPart Availability: ease of acquiring parts to build and replace in order to

service when repair is neededLife Span: length of mission the device as able to sustain measuring

devicesPackage: ease of fitting all components inside the hullMaintenance: ease of repair, device must fairly easy to disassemble and

fixCommunication: ability of device to transfer data to base station for analysisPower Consumption: power used by deviceCapability: the number of tasks the vessel can achieve

Once all of the criterion were determined and defined, Pugh’s Method was utilized to assign weight to each of the variables.

After the criteria were weighted according to their importance (Appendix A.1), they were crossed referenced to the three design ideas with the surface vessel set as the base concept. Due to the style of this method, and the quantification of a relative increase or decrease in the given criteria, a score of three is considered baseline. Thus, for a concept to show improvement over the baseline its combined score must be greater than three. Results are provided in Appendix A.2.

The calculations show all the designs to be relatively similar. While the electric surface vessel won out by a slight margin, the design team felt that the increased capability of the submersible design should not be ignored. Upon re-inspection of the concept feasibility voting results, it


was determined that the two main shortfalls of the submersible concept were the weight and difficulty criteria.

The concern relative to weight with regard to the submersible was mainly in the excessive weight in the design of the ballast system. Therefore it was decided that in order to incorporate a submersible design a significant weight reduction in the design of the ballast system would be crucial. The group also decided that the ballast system should not be designed in such a manner so as to prohibit the design of a vessel capable of surface research, should a light weight ballast system design prove to be beyond the scope of the project.

The other major shortfall, difficulty, was analyzed to determine if improvements could be integrated into the design. The main complexity of the submersible concept was found to be resultant from the desire to provide underwater navigational capabilities. While surface navigation can be easily accomplished via the utilization of GPS, the inherent properties of a water medium provide to negate the possibility of GPS for submerged location finding. Thus, a study into information on the possibility of navigation via inertial means, and or utilizing magnetic compass devices was conducted. Both means proved to be quite cost prohibitive.

The previous generation of the SADCATS project incorporated static diving capabilities. Even though the complexity of a dynamic-dive and submerged navigation system was proved to be prohibited by budget and time factors for the scope of the project at hand, the possibility existed for the incorporation of a static dive system within the timeframe allotted.

The design decided on for the second generation of SADCATS will incorporate both surface navigation and static diving. A ballast system in the rear of the sub will be used to control diving via an air/water bladder. The vessel will only be capable of surface navigation by using two propellers mounted on the side of the vessel. These propellers will


not only control forward propulsion but will also be used to change direction. The sensors that will be used include temperature, pressure, color, and turbidity along with a GPS module.


4.0Design and Performance Parameters4.1 Design Objectives

The design and production of the SADCATS project is to be considered complete when the following deliverables are met:

The finalized design accomplishes all of the required taskso Data acquisition is accurate and within the specified toleranceso Data transmission is accurate and reliableo The control software is robust, fully capable, and easily modifiableo The vessel is capable of accurate navigation via GPSo The vessel is light weight and easily transportableo The vessel and related electronics are capable of autonomous

deploymento The vessel is able to perform its tasks over the full mission lengtho The vessel is within the required budget

All options have been exhaustively analyzed, discussed, and processed The design is properly documented so that future users can benefit

from the work accomplished by this years project team All project deadlines, both internal and external have been

satisfactorily met The design provides the means for addition of other payloads in the

future

4.2 Performance Specifications

Among with the design objectives, there are a number of specific performance specifications that are to be met in order for the SADCATS project to achieve successful completion. They are as follows:

A. Dive Depth: The maximum dive depth of the vehicle is to be 100ft

B. Horizontal Speed: The vehicle is to achieve a surface speed of at least one

knot.

C. Target Mission Length: 16 Hours (Daytime Deployable)document.doc 23 SADCATS

D. Tracking Range: Data points can be taken from 30km outside Rochester

4.3 Design Practices Utilized

The SADCATS vessel has been designed utilizing the following principles:

A. Design for Manufacture: All parts of the design have been selected and designed with easy of manufacturability in mind. All custom parts can typically be made on premise for users with an engine lathe and upright milling machine.

B. Design for Assembly: The overall design of the vessel is such that it can be constructed using commonly available tooling. It is also such that no special training is required to assemble the vessel.

C. Utilization of Common Hardware and Materials: The design incorporates hardware and materials that are commonly available. The end user will thus benefit due to the easy of part replacement.

D. Design for Expandability: The vessel is structured such that additional payload sections can easily be incorporated. This provides the user endless possibilities for data collection and or scientific experimentation

E. Economical Design: Without compromising integrity, the design incorporates a low cost solution, thus allowing the end user to maximize return on financial investment

F. Recyclability: The SADCATS vessel has been designed to allow for ease of recyclabiity. This includes the reuse of some items, and the separation and sorting of those parts not reusable.

4.4 Safety Concerns

Due to the nature of the project, there were many safety standards to be taken under consideration. The foremost is that of the ASME Boiler and Pressure Vessel Code. Other design standards include, but are not limited to Cost Guard specifications for small scale powered watercraft and research vessels, and FCC regulations governing radio transmission. As always, electromechanical devices present some risk of shock, and this risk is increased due to the utilization of the design in water environ.


5.0Analysis and Synthesis of Design Elements

5.1 Mechanical Design

5.1.1 Hull

The hull of second generation SADCATS design has been modified greatly from that of the original variant. When compared to the previous generation, the urge to lower weight and add directed mobility were the main driving factors for such a radical redesign. Thus the design of the hull was greatly dictated by the internal component requirements in addition to the need for a streamlined profile to minimize losses while in motion.

Due to the requirement of the vessel to have the capability to submerge, the hull is subject to pressures not typically experienced during surface mobility. When one travels below a fluidic surface, the pressure distribution experienced is defined by the expression

P=Patm+ρgh Equation 5.1.1

Thus as a general rule derived from the density of water as a fluidic medium, for every 33 feet one dives, they experience one additional atmosphere of pressure. Based on this rule, the vessel design must be able to withstand four atmospheres of pressure.

Based on electrical requirements of the dictated GPS navigation system, the material of the vessel was required to be non-metallic in nature, so as to not interfere with communications between the GPS sensor and its satellite communications. Thus it was a direct goal of the design to provide a solution that utilized such material.

Moreover, due to propulsion and stability theory as found in sections 5.1.3 and 5.1.4 respectively, it was determined that the vessel would be most stable when the latitudinal cross section was symmetric about the vertical plane traveling through the geometric midpoint of the vessel. In an effort to reduce drag, contoured surfaces were


investigated. The geometric strength of the design was also analyzed due to the external pressures seen during service. In addition, the possibility of internalizing the ballast system was investigated.

The resultant hull design was dictated largely by concerns for structural rigidity and low resultant drag. The above considerations where also included in the analysis. As the sponsor is providing a means the outsourcing of some fabrication tasks, the hull design also reflects discussion with the fabrication facility.

The second generation SADCATS hull design thereby incorporates the use of three composite materials in its design. The need for color sensing technology provided a necessity for a transparent hull portion to allow for light feed back to the color sensor. Therefore Plexiglas Acrylic has been selected for the hemispherical front section. The Plexiglas material will provide machinability during the fabrication phase, while maintaining high optical qualities as required.

The center sections of the hull have been designed to be fabricated from Schedule 80 Polyvinylchloride (PVC) pipe. Due to the need to compartmentalize the hull sections, PVC was chosen as a low cost solution to the need for a durable material that would provide easily modifiable components.

Finally, the tail section is to be comprised of Acrylonitrile Butadiene Styrene (ABS) material. The ABS material provides excellent mechanical properties and an inherent easy of machinability. It thus provides a means for the internalization of the ballast system in the rearward section of the submersible.

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code was used to derive a means for the proper specification of material thicknesses and verification techniques for the hull design. As dictated by the ASME in Section X, the vessel is to be considered a Class II vessel and due to service under both external and internal pressure, is to be analyzed via Finite Element Analysis (FEA) for stress and deformation under load as specified by Method B of Section RD-11. Material Data Properties for the hull materials can be found in Appendix with corresponding FEA results in Appendix. The following table provides results for the analytical analysis of the hull,


based on a wall thickness corresponding to that of Schedule 80 PVC piping, and calculations provided in Section RD-11 for Method A design.

Table 5.1.1

While the PVC Schedule 80 pipe would not be able to withstand the required design pressure, the inclusions of divider walls between sections of the main hull section shorten the effective length of the PVC Schedule 80 sections and thus increase the range of operation pressure.

Based on the initial calculations under the scope above, the vessel was designed utilizing the PTC Pro/Engineer and Pro/Mechanica analysis packages. With the solid model created, the vessel structure was subjected to loading in the three following cases:

Full Ballast System to Achieve Dive from Surface: 165psi internal pressure


Empty Ballast System at Depth for Accent: 90psi external pressure

Combined Loading State: 90psi internal and 165psi external pressures

The analytical results are provided in Appendix !!!!!!!. From the resultant models, it can be found that maximum material deformation is with in reasonable tolerances for the scope of the project. The stress loadings of the vessel are also within the specifications dictated by the ASME pressure Vessel Code

5.1.2 Ballast System

One of the major downfalls to the first generation SADCATS design was the weight of the ballasting system. The previous system required the need to transport compressed air in order for the vessel to regain positive buoyancy after a dive. Thus a major design consideration of the second generation dive system was to allow for the ability to submerse and resurface without carrying excessive weight as a functional requirement.

Another specific requirement derived from the desire for a mixed mission capability incorporating surface travel was the need to create the capability to rotate the vessel upon its horizontal axis when diving. With the negation of dynamic diving capabilities, it was determined that this style of dive was most logical in nature. Thus the ballast system has been designed to create a moment such that the vessel will orient itself tail down during the dive phase. Decent and accent are both then accomplished in a near vertical manner, with the tail mounted water outlet serving to aid in thrust during the accent.

From a design standpoint, the ballast system is required to alter the buoyancy of the vessel from a positively buoyant, surface mode to a negatively buoyant, diving mode. For the vessel to hover at a specific depth the buoyancy of the vessel must be neutral. As the force of buoyancy is defined as


Equation 5.1.2

As the vessel displaces a volume that is dictated by its height in its submersion medium, the permissible weight of the vessel is directly correlated to its desired “ride height” in the water.

In turn, the static ride height of the vessel then dictates the requirement for the ballast weight necessary to create neutral buoyancy. The ballast system is then designed to allow the vessel to add mass to achieve a neutrally buoyant state to allow for the dive condition. The table below lists the ballast system characteristics for the SADCATS ballast system, based on critical design parameters derivative of the hull design process.


Table 5.1.2

The second generation SADCATS ballasting system therefore implements a pressure differential system accomplished via the use of a water bladder enclosed within a pressurized air chamber. As water is introduced via pump into the bladder to add mass and change


buoyancy, the air is pressurized above its static condition. The water is then expulsed through the tail section of the vessel via the accumulated pressure under the control of a solenoid valve. A Schrader valve allows for ease of filling and adjustment to the internal air pressure. A pressure sensor installed in the ballast wall provides feedback to the controller, which can open the solenoid valve in an emergency situation.

Diagram 5.1.1

The generation one SADCATS ballast system consumed a large portion of the vessel volume, while this years system have been reduced to less than 25% of total vessel volume. The reduction in weight is significant, with the second generation system weighing less than five pounds when dry, which in turn is only 20% of the total dry weight for the second generation SADCATS.

Provision for the dive system due to the mass transfer resultant of the ballast system design allows a dive to full 100ft depth in a maximum of 15 seconds. The sizing of the corresponding solenoid valve was determined imperially with the calculations found in the following figure


Figure 5.1.3

Full Ballast Tank (Diving) at DepthInternal Pressure Pint 126.93 PsiExternal Pressure Pext 58.04 PsiWater Density ρ 1.94 slugs/ft³Velocity V 101.1279 ft/sMass flow for 1/8" m1/8 0.53793 lb/secTime to Neutral Buoy T1/8 2.46053 SecMass flow for 1/4" m1/4 2.15173 lb/secTime to Neutral Buoy T1/4 0.61513 Sec

Neutral Buoyancy to Empty Ballast TankInternal Pressure Pint 85.47 PsiExternal Pressure Pext 58.04 PsiWater Density ρ 1.94 slugs/ft³Velocity V 63.819 ft/sMass flow for 1/8" m1/8 0.33948 lb/secTime to Empty T1/8 22.09286 SecMass flow for 1/4" m1/4 1.357905 lb/secTime to Empty T1/4 5.52322 Sec

Area of 1/8" Orifice A1/8 0.012272 in²Area of 1/4" Orifice A1/4 0.049087 in²

From the data above, a solenoid with a ¼” orifice was selected. It is estimated

that so equipped, the SADCATS generation two vessel would reach a maximum

velocity of less than 20 feet per second.

5.1.3 Propulsion System

Part of the required capabilities of the second generation SADCATS is the

ability to collect data at different waypoints. Calculations for propulsion take into

account various aspects of the sub and its environment. Such variables as

estimated speed, density of traveling medium, and surface area must first be

considered to find the drag force. The estimated speed of 1 knot is the value the

group decided on. The density of the traveling medium is dependent of the

temperature. Surface area was found via CAD modeling. The hull sections were

made separately and then sliced to mimic the vessel as it would sit in both 4 and 5

document.doc 32 SADCATSSchrader

ValveInlet Pump

inches submerged in water. The drag force is the reaction force the sub will

experience while traveling through the water. The drag force is important to

know because in order to obtain forward motion, the drag force must be

overcome. Refer to the below equation:

FD = ½*CD**V2*A

CD is the coefficient of drag. The coefficient of drag is solely based on the

geometry of the part that the fluid is moving over. The coefficients for each hull

section were found in table.

A flow analysis was then configured for the hull. A Reynolds Number was

found for each section of the hull for the estimated speed over the temperature

range the sub would operate in. The viscosity of the fluid, speed of the fluid and

the affected length are used to find the Reynolds number. The dimensionless

value of the Reynolds Number is an indication of the nature of the flow. The

equation to calculate for Reynolds Number can be seen below:

Re = V*L/

Ideally, we would like the sub to operate in a laminar flow. A laminar flow

means that all the molecules of the medium in which the sub is traveling in are

aligned. If the molecules of the fluid are aligned, the friction the surface

experiences, is at a minimum. For a flow to be considered laminar Re must be

less than 5x105.

The complete flow analysis for the vessel is located in Appendix.

The next consideration in relation to propulsion is thrust. Thrust is the force

exerted by the propellers to achieve motion. The value of thrust is influenced by

the major diameter of the propeller, the speed of advance, the density of the fluid

medium and the rate of rotation for the propeller. The speed of advance is our

estimated speed. The major diameter of the propeller we made as a flexible

dimension. Below is the equation for thrust:

T = *V*D3*N

Propulsion is not a perfect method of forward movement. Slippage is defined as

a ratio of the speed attained divided by the speed the vessel exerts for. The

calculation for slippage is below:


s*(s + 1) = CT

Slippage also takes into account the thrust coefficient, CT . The thrust

coefficient is an offset to account for the propeller’s major diameter, revolutions

that the prop turns per sec and the density of the medium. The equation to

calculate for CT is below:

CT = T / *N2*D4

Pitch is a dimension of a propeller that corresponds to distance traveled per

revolution of the prop. If a prop has a pitch of 2.5 inches, its ideal performance

would provide 2.5 inches of forward motion to one revolution. The theory behind

slippage infers that a propeller doesn’t perform to specification. Slippage is a

function of a vessel’s thrust coefficient.

The torque coefficient is a factor that is a ratio of the applied thrust force with

respect to the density, rate of rotation of the prop and the major diameter of the

propeller. The equation of the torque coefficient can be seen below:

CF = FT/*N2*D5

Another factor that must be considered is speed of advance coefficient, J. J is

an independent variable that is used to find the efficiency. The speed of advance

coefficient can be found using the equation below:

J = V/N*D

Efficiency of the propeller is very critical. If the efficiency of the propeller is

known or can be closely estimated, losses can be planned and compensated for.

The efficiency of the propeller is found from a table where the speed of the

advance coefficient, the torque coefficient and the thrust coefficient are plotted

against each other.


Left y-axis is the Thrust Coefficient, CF

Right y-axis is the Torque Coefficient, CT

The x-axis is the speed of advance coefficient, J

The calculations located below allow for determination of a motor and a propeller

simultaneously. The propeller can be sized accordingly in order to achieve

maximum performance. Vender feedback will determine the motor. The

calculations below use an example propeller.

Propulsion Calculations

Propeller Dimensionsmajor diameter D= 2.52 inpitch P= 3.9 indisk area of propeller A0= 4.99 in2

Flow AnalysisMax Drag Force FD= 1.89 lbf

Other Variablesdensity of fluid 0.001123 slug/in3

speed of advance Va= 40.56 in/srevolutions per unit time N= 66.667 rps


Propeller Calculations Thrust, T = VaD3N

T = 48.595 in*slug/s2

T = 4.050 lbf

Resultant Thrust, TR = 2.160 lbf

Thrust Coefficient, CT = T/2D4

CT = 0.241 Resultant Thrust Coefficient, CTR= 0.129

Torque, Q = (TVa)/(2piNI)

Q = 0.45096 lb-inQ = 7.2154 oz-in

Resultant Torque, QR = 3.848 oz-in

Torque Coeffecient, CQ = Q/N2D5 CQ = 0.01067

Resultant Torque Coefficient = CQR

= 0.00759

Slippage, s = (1+4*CT).5 -1 s = 0.231

Ideal Efficiency, I = (1-s)/(1-s*.5)

I= 0.870 Speed of Advance Coefficient, J = Va/ND

J = 0.241

A motor originally was found that met the requirements from a mechanical and an

electrical engineering standpoint. However, due to the extended lead time the order for

the motor was cancelled. Another motor was found at a local store, Dan’s Crafts and

Things, that provided similar electrical requirements but the torque was lower than

originally planned for. In testing this motor in the propulsion assembly, it was found that

the torque was not large enough to turn the propeller through the lipseal. Because of time

constraints, the next available option was a hand drill motor.During the course of


designing the propulsion system, there were two main concerns. The

first concern was how the system would be sealed under static and

dynamic conditions. The second concern was the alignment of the

shaft under loading. A seal around the propeller shaft must be able to

prevent leakage while operating near the surface as well as provide

static sealing while diving to 100 feet.

It was advised that a radial lip seal be used to give the

propulsion system proper sealing under both conditions. The

information below was found in a text that describes the functionality

of a lip seal.

An elastic circular member with a beamlike cross section is bonded to a rigid case (figure xxx). The inner diameter of the elastomeric

beam is smaller then the shaft outer diameter. The difference between the shaft outer diameter and lip inner diameter is called

interference. When the seal is installed, the elastomeric lip is stretched outward, which creates a force between the sealing tip and the shaft.

(reference from lip seal book page 10)

INSERT Lip Seal FIGURE HERE!!!

The function of the lip seal is very critical. If the lip seal doesn’t

prevent leakage, water will fill up the propulsion assembly and possibly

cause other systems in the submarine to fail. Not only does the

sealing ability of the of radial lip seal affect the sub as a whole, the

friction of the seal affects the ability of motor to rotate the propeller

shaft.

Previous configurations didn’t take into account the friction of

the lip seal. After assembling the system it was found that a motor


with greater torque capabilities would be required to overcome the

friction of the lip seal.

Other locations where sealing must be taken into account are the

interfaces between the plates at either end of the motor tube. It was

planned to use PVC pipe to house the propulsion assemblies. Holes

were taped into both ends of the PVC pipe to allow for plates to be

bolts to them. Bolt circles were configured so that their force was

distributed most efficiently across the bolts to provide best possible

sealing scenario. The equation below was used to create the desired

bolt circle.

3 < D/N*d < 6

By varying “N”, one can control the proximity to either 3 or 6.

Numbers closer to 3 correlate to space required for wrench clearance

and numbers closer to 6 correlate to spacing for uniformity. Since a

uniform seal was our greatest concern, our bolt circle calculations drew

closer to values of 6.

Through testing, it was found that a gasket is necessary to

prevent leakage into the propulsion assemblies. Cork-rubber seals

were cut to size for both the front and back of the enclosure. Previous

experimentation proved that a torque wrench was not a suitable tool to document.doc 38 SADCATS

Variable DescriptionD Diameter of bolt circled Diameter of boltN Number of bolts in bolt circle

apply torque to the bolts. Threaded holes were stripped by trying to

use a torque wrench. A stripped hole makes the interface between the

end plate and PVC wall much weaker. It was then decided that all the

bolts had to be “hand tight”. This specification is very arbitrary,

though it was needed since the PVC is much softer than bolts used for

clamping the ends of the propulsion assembly.

As a result of the arbitrary torque requirement of the bolts, the

applied gasket pressure is also arbitrary. Calculations were still

completed to provide information on a how much pressure should be

applied to the gasket. Applied force to the gasket was limited due the

properties of the PVC. To prevent destruction of the PVC threads, 1/3

the magnitude of the PVC yield stress was calculated and used as a

reference for the applied force. Gasket pressure calculations are found

below.

Yield Strength of PVC = 2466 psi

Fm = (1/3) * (Yield Strength of PVC) * Area of bolts

Variable DescriptionFm applied force to gasketAg area of gasketN number of bolts

Gp = Fm / Ag / N

Part of the effectiveness of a bolt is the length the engagement

provided by the threads of that bolt. The pitch and diameter of the

bolt determines how much should be threaded into the mating


material to be adequate. The below equation was used to determine

this specification:

Le = ( 2*At ) / .5** ( D - .64952p )

Variable Descriptionp screw thread pitchD nominal diameter of screwAt tensile stress area of screw

Another aspect of important consideration for the propulsion system is the

alignment of the shaft under loading. A thrust bearing was integrated into the

design to provide linear and axial stability of the shaft while adding minimal

friction. The total length of the shaft is approximately 7 inches and would have a

tendency to wobble under loading sustained while used.

The shape of the propeller required that the shaft would need a geometry

to fix the propeller in place while in motion. Initially, it was ideal to have a drive

dog be machined onto the propeller shaft. This would allow the propeller to fit

into a key way. However, the drive dog is complicated to machine, especially

with time constraints. The final idea was to fit the propeller onto the shaft by

using a split pin that had to be press-fitted into the shaft. The propeller would

then be clamped on by a washer and nut. The picture below is the final propeller

– shaft mating scenario.

INSERT PICTURE OF PROPELLER SHAFT!!!! (Figure ???)

The use of the split pin allows for a good technique to fix the propeller to

shaft. However, removing material from the shaft creates a weakness that must

be analyzed. The torque of the shaft is limited with respect to the diameter of the


pin, diameter of the mating shaft, and the shear yield strength of the shaft

material.

Tcapacity = *d2*D*Ssy / 4

Another machine characteristic of the propeller shaft is

the stress concentrated created by the narrowing of the

diameter. This is also a weakness that would limit the

strength of the material. The below equations state the

variables that adjust for this phenomena. Kt is the variable

that is an offset that is found by correlating D, d and r.

nom = 16*T / *d3

max = Kt*nom

It’s important to know the amount of torque that can be

applied to the shaft due to the stress concentration. Though

we can also figure out what the shaft can handle simply from

material properties. Aluminum was chosen because it’s a

lower density material. A lower density material would be

easier to rotate through the lip seal and would require a

smaller motor to be used. A very rough estimate of the document.doc 41 SADCATS

Variable Descriptiond pin diameterD shaft diameterSsy shear yield strength

Variable DescriptionD major shaft diameterd minor shaft diameterT applied torquer radius between diameter change

torsional yield strength can be obtained by assuming that the

tensile yield strength is between 60% and 90% of the tensile

strength.

*******

5.1.4 Stability Control

The concept of stability can be seen most easily when considering what happens

when the vessel is inclined from the vertical axis due to some external moment on

the body. In equilibrium, the center of gravity of the vessel is directly above the

center of buoyancy. When an external moment is applied to the body, a heeling

moment occurs. That is to say, the vessel moves away from its state of initial

equilibrium. As long as the vessel has the properties of stable equilibrium, a

righting moment will occur after the removal of the external moment.

Along with the center of gravity, the metacenter of the vessel needs to be

considered. The metacenter is basically a pivot point and can be seen

schematically by drawing a vertical line upwards from the center of buoyancy at

initial equilibrium and at some given incline. The intersection of these lines is the

metacenter. This concept can be seen in Figure 1. The usefulness of this point

can be seen in determining the stability of the craft. The goal is to have the

metacenter located above the center of gravity; this will create a stable

equilibrium. Also, the farther the center of gravity and the metacenter are from

each other the greater the righting moment is (assuming the center of gravity is

lower than the metacenter).


o o

GB1

W1L1

W0

L0

o B0

o M

The position of the metacenter can also be determined through the use of several

equations by considering a slight inclination from the vertical. The two triangles

produced at this inclination (W0OW1 and L0OL1) must be equal in area. In figure

2, the distance y is the half-ordinate of the original waterline while the center of

gravity moves from two thirds of this value on one side of the center line to two

thirds of the half-ordinate on the other side. Therefore if the moments of volume

are considered, the resulting moment is given by:

* 0∫L (2y3/3) dx

where 0∫L (2y3/3) dx is equal to the moment of inertia, I, of a waterplane about

its centerline. Therefore the resulting, or excess, moment is equal to IAs can

be seen in figure 2, the center of buoyancy is just the excess moment divided by

the volume of displacement.

BB1 = IQ/V

The distance BM is then equal to the inertia divided by the displaced volume.

BM = I/V

The height of the metacenter can now be defined as the difference from the center

of gravity to the metacenter point.


yW0

W1

2/3y L1

L02/3yy

B0 B1

M

K

In regards to stability of a fully submerged vessel, the concept is very similar to

that of a surface vessel. The main difference is that for a submerged vessel the

center of gravity is located below the center of buoyancy. This S.A.D.C.A.T.S.

design incorporates a ballast tank in the rear section of the hull. This will cause

the vessel to submerge tail first. With a full ballast tank the center of gravity will

have shifted from its original location to a location closer to the rear of the sub in

closer to the centerline of the sub.

5.1.5 Component Mounting System

The component mount rack was designed to accommodate all of the electronic controls in such a way that they will be secure while the vessel is in and out of the water. The mounting rack was designed to be of light weight and still be structurally stable while supporting the electronics. The rack comprises of three shelves, two supporting rings, and is located in the front two sections of the hull.

PICTURES


5.2 Electrical Analysis & Synthesis

5.2.1 Microcontroller Selection and Design

5.2.1.1Selection of Microcontroller (Atmel, ATmega128)

The Atmel ATmega128 was chosen because of its computational ability, quantity of input/output pins, and ease of programming. Of primary concern was the ability to calculate floating point numbers, which would be useful for calculating angles and storing sensor data. This capability was lacking in the BASIC Stamp used in the previous generation SADCATS. The ATmega128 has a low cost of about $5, while the BASIC stamp came as a package and cost around $100.

In addition to its low cost, the ATmega128 consumes power at a comparable rate to the BASIC stamp. It also contains 128kB of program memory, and 128kB of data memory, which is useful for storing the data to be collected.

Another option investigated was the Handy Board, which has a sufficient processor for handling the required calculations. However, since the chip itself is only a microprocessor, an additional I/O interface would need to be designed to handle connections to sensors and controls. Because of this, board layout becomes more difficult due to extra components, which also use more physical board space than the ATmega128, which contains all needed components.

5.2.1.2 Integration with Electrical System

Since the microcontroller is required to communicate with the sensors, motors, and other electrical devices, each needed input and output pin was designated based on the requirements of the system.

Microcontroller pin requirementsA/D input pinsBattery Voltage Sensor #1: Any Port F pinBattery Voltage Sensor #2: Any Port F pin


Temp Sensor: Any Port F pinPressure Sensor #1: Any Port F pinPressure Sensor #2: Any Port F pinColor Sensor: Any Port F pin

Serial I/O pinsGPS: UART 0, Port D pins 2 and 3Modem/Radio: UART 1, Port E pins 0 and 1

General I/O pinsTurbidity/Conductivity Sensor: Any two general purpose pins (virtual serial connection)Radio Tx/Rx Select: Any general purpose pinSolenoid Valve Control: Any general purpose pinColor Sensor Mode Control: Any two general purpose pinsStatus LED: Any general purpose pin

PWM output pinsMotor #1: Port B pin 4, 5, 6, or 7Motor #2: Port B pin 4, 5, 6, or 7Pump: Port B pin 4, 5, 6, or 7

5.2.1.3Organization of Program Structure

The program structure was broken into phases for purposes of a control outline. Flowcharts and psuedocode are provided in Appendix .

A. Initialization PhaseB. Waypoint Determination PhaseC. Waypoint Seek PhaseD. Dive Cycle PhaseE. Rise Cycle/data Collection PhaseF. Transmission Phase


Steps B through F are repeated until the vehicle detects a low battery state, upon which it enters into a phase where it will transmit its location and await retrieval. This transmission will occur once per designated time interval (Potentially this occurs every time a signal is read for the GPS; t=1sec).

Upon startup initialization, the vehicle will check its battery voltages and flash a code on an LED enclosed in the clear end cap if one or both batteries are low to alert the person deploying the craft that there is a problem. If both batteries are okay, the vehicle will flash a continuous signal for 3 seconds. The craft will then wait for several minutes before beginning its algorithms so that the motors and other devices will not kick on until after it has been placed in the water. This also gives the GPS time to initialize.

5.2.1.4Waypoint Seek Algorithm

Since the vehicle may have a heading of any direction, the system must be able to control the angle at which the vehicle will travel with respect to the waypoint. The goal of this is to reduce the angle error of heading with waypoint direction to zero. To do this, two vectors are constructed using the data from the GPS.

First, the movement vector, of previous position to current position will be determined, and then the error vector of current position to waypoint position will be determined. To find the angle error, the error between these two vectors will be calculated as follows:

Equation 5.2.1

(Eq 5.2.2)


This angle will be from 0 to 180°. In order to determine which motor should receive less power, it is important to know whether this is a negative or positive angle. To do this, the slope of each vector will be calculated, and the results are as followed:

Table 5.2.1Case True IfAngle is 0 to 180°

ORAngle is 0 to –180°

OR

If the angle is 0 to 180°, then the craft must turn to the right to correct the angle error, and thus the right motor will be reduced in power proportional to the angle error plus the integral angle error. The left motor will be full power.

If the angle is 0 to -180°, then the craft must turn to the left to correct the angle error, and thus the left motor will be reduced in power proportional to the angle error plus the integral angle error. The right motor will be full power.

Equation 5.2.2

(Eq 5.2.2)


5.2.2 Power Electronics Board

5.2.2.1 Diodes (Vishay, 1N5820)

Diodes are used on the power electronics board to prevent backflow into the batteries so that they can be configured in parallel and have a more even drain on their charge. This results in a larger total capacity without the need for an array of FETs to switch between battery packs.

A parallel configuration of the packs allows for less voltage drop across the battery when a load requires a large current draw. This is the case when the pump is running, as it can draw up to 8A. The chosen diodes will have a maximum forward voltage of 0.475V, and thus the maximum power loss due to the diodes will be at most 4% in worst case scenario.

Six diodes are used on the board with each of the six battery packs followed by a diode.

5.2.2.2 Power FETs (Motorola, IRF540)

Power FETS are used to switch on and off the heavier load electromechanical devices. There is one FET for each Motor, one for the Pump, and two for the Solenoid Valve. The FETs that are connected to the motors and pump have their gates connected to the PWM channels of the microcontroller. This allows these devices to be run at a variable speed. The solenoid valve is connected to a FET whose source connects to the motor battery pack, and one whose source connects to the communications & control battery pack. This is for emergency surfacing in case the motor pack dies while the vehicle is submerged.

The FETs were chosen to be able to handle a high continuous drain current, due to the high current draw of the pump. The chosen FETs have a continuous drain current rating of 19A at 100°C, with a PDS(on) of 0.07. This means that at the worst-case scenario, there is a power loss of (.07*8A)*8A = 4.48W. This translates to at least 95%


efficiency at the worst case. Since this worst case occurs infrequently, the nominal efficiency is much higher. For the drive motors, the worst-case power loss is (.07*1.5A)*1.5A = .1575 watts. This is an efficiency of better than 99%.

5.2.3 Communications

A goal of the design team was communication of vessel location, via radio transmission. This is essential attribute that allows vessel retrieval on a large lake like Lake Ontario. Additionally, transmission of vessel status and the collected scientific data would be very useful.

Communication stretching from a base station at Rochester Institute of Technology (RIT) to large portion of Lake Ontario is necessary so that the vessel can maintain communication. Thankfully, an antenna at RIT can communicate with a station on the lake almost Line-of-Sight, allowing a good range on any of the 144-148Mhz, 222-225Mhz, and 420-450Mhz bands at low transmitting power. Additionally, any shortcoming in the vessel’s antenna can be mitigated by the selection of the base station antenna at RIT, where a significantly larger and more suitable antenna design can be utilized.

5.2.3.1 Modem and Radio Transceiver (Chipcon SmartRF CC1000)

A modem is needed to take data, such as serial GPS data, and modulate it into frequency information. A radio is needed to move the modulated signal to the appropriate frequency range.

Two possibilities were given serious consideration, a simpler pricier solution and a more complex but cheaper and more compact solution. The simple solution was to use the Maxim modem chip used by last year’s team, and connect the chip to an amateur radio band transceiver, which is a handheld size device. Most handheld transceivers offer 5 Watts output power, and often have a low-power output mode.


The more complex option, is use of the Chipcon CC1000, an IC that performs both modem and transceiver functions in one chip. The chip’s output power is 10dbm, or 10mW, thus use of the chip would require an amplifier module to step up the chip transmit output. A Tx/Rx switch to toggle the amplifier in and out of the circuit is also required. However, this combination of parts is cheaper and is a slightly more compact space-wise. The CC1000 is confined to a range of 300 to 1000Mhz, which means the vessel would need to transmit on the 440Mhz band. Another useful feature is of the CC1000 is the programmable output power, selectable from –20dBm to 10dBm in 1dDm increments. This allows fine control over output power.

5.2.3.5Radio Amplifier, and Tx/Rx switch (Mitsubishi, RA07H4047M, Ramsey RFS1 Kit)

The radio amplifier chosen is a compact four-pin module that is capable of 10W output for 10mW input, which is the capability of the Chipcon CC1000.

5.2.3.6GPS (Garmin GPS-35)

The GPS chosen by the team is a module that has no interface aside from a serial connection. This allows the vessel to travel to data points, and allows the user to locate the vessel for retrieval. The GPS has an absolute accuracy of 15 meters, but relative accuracy is much better, usually less than a meter. A WAAS-capable GPS with an accuracy of less than 3 meters was considered, but it was found the client had no need for the increased absolute accuracy.

The GPS supplies the Microcontroller with positional data once every second, and this allows re-calculation of speed and heading once a second.

5.2.3.7Antenna

The antenna of the craft must be tuned for the 440Mhz band, be omni- directional, and be unobtrusive enough to not affect vessel drag and stability. A ¼-wave single element antenna measuring


approximately 7” is chosen by the team, because it requires only one puncture of the hull and creates little drag. The antenna could be cut from a standard car antenna, as that would provide flexibility and ensure that the antenna does not break off during user handling. The antenna could also be used as a mount for a florescent orange flag, enhancing the vessel’s visibility. A longer ½-wave type antenna could be used if the longer length did not create handling problems for the user deploying the vessel.

5.2.3.5 Data flow, error detection and error correction

A few possibilities for increasing the reliability of transmission are still being considered by the team at the time of this report. A simple strategy would be to send transmit ASCII-encoded data to the base station, and wait for an ACK, a keying of the receiving station indicating it acknowledges the signal. An addition to this, Hamming Coding or some other method can be used to provide some data redundancy and allow one-way error detection and correction.

5.2.3.7Legal Restrictions

The FCC Code of Federal Regulations Title 47, Volume 5, Part 97, Section 97.301. grants use of the 144-148Mhz, 222-225Mhz, and 420-450Mhz bands, among others, to license-holding amateur radio operators, known as “Hams” (see Figure 5.2.4.1) One of the team members, Matthew Stith, is a licensed technician-class amateur radio operator, as is Dr. Kremems of the College of Imaging Science. While the vessel is under a control of a licensed Ham, the FCC part 97 rules allows the vessel to transmit and receive data on the allotted frequency bands provided the Ham has licensed access to those frequency bands.Figure 5.2.4.1


5.2.4 Data Acquisition and Sensory Package

5.2.4.1Pressure Sensor (SenSym ICT, 19C-100P-A-6-K)

In order to ensure an accurate measure of depth, various pressure sensors were examined in order to provide a large range of pressures, a high degree of linearity, and easy integration with the microcontroller. Since the maximum required dive depth was set to be 100 feet, which is roughly 58psia, a sensor was selected to go well beyond this range.

The sensor selected provides a reading of 1mV/psi, with a maximum zero pressure offset of ±2mV, but typically has no offset. The operating range (full-scale span) of the sensor is 0-100psi, with ±0.1% pressure nonlinearity. The effect on this reading by temperature is only a maximum 0.5% of the full-scale span, so this sensor will be relatively accurate. It receives power from a 12V connection.

In order to receive input from the sensor through an A/D channel on the microcontroller, the voltage will be scaled from 0 to 3V in order to account for a possible unexpected pressure surges. Since the A/D channel is 10 bits wide, the resolution of the pressure will be .163psi/level, or 6.135 levels/psi. In order to accomplish this task, an amplifier will be constructed using an op-amp circuit.


5.2.4.2 Temperature Sensor (Analog Devices, AD592CN)

Since temperature was an important quantity to measure, the temperature sensor was selected to provide accurate, linear measurement. The range of operation was selected from 0°C to roughly 32°C. The sensor itself has a total range of -25˚C to 105˚C. The temperature sensor receives power from a 5V connection.

The AD592CN has a temperature coefficient of 298.2μA/°C. This is scaled using a voltage dividing circuit and calibrated to then output 10mV/K. Since the range of input of interest is 273.2K to 305.2K, this would mean that the output would need to be shifted by 2.73V in order to set 0°C as the 0V point. Since the range is now 32K, or.32V, this is scaled to correspond with the 5V limit of the A/D channel. A difference amplifier implemented using an op-amp circuit performs the scaling and shifting.

As configured, analysis of the difference amplifier results in the following equation:

Equation 5.2.3

In order to scale 0.32V to 5V, we select R2/R1 = 5V/0.32V, or about 15.625. Here, a higher gain would result in a lower maximum temperature, and if this max temperature is set to 82°F, a gain of 18 could be used. This shift of the sensor output, results in .03125°C/level, or 32 levels/°C.

5.2.4.3 Turbidity/Conductivity Sensor (Honeywell, APMS-10G)

Turbidity and Conductivity of the water were also useful quantities to measure, and thus a sensor with dual capability was chosen in order to make the sensor interfacing simpler. This turbidity sensor uses a serial port connection to the microcontroller, and collects data when a


request signal is transmitted to it. It receives power from a 12V connection, but is compatible with a varying input from 8V to 30V.

Turbidity is a measure of the degree to which light traveling through a water column is scattered by suspended particles in the water and is measured in Nephelometric Turbidity Units (NTU). The selected sensor can measure turbidity from 0 to 4000 NTU, with a maximum response time of 1.3 seconds.

Electrical conductivity is measured in mSiemens, with a range of .0001 to 15. The response time for said measurement is .85 seconds.

Since the turbidity/conductivity sensor interfaces with the controller through a serial port connection, no extra circuitry is needed to scale or shift the signal. Data is collected when an activation signal is transmitted to the sensor.

5.2.4.4Color Sensor (Taos, TCS230)

The color sensor is used to detect the intensity of light in the water from each color component of light. It is designed to measure red, blue, green, and white light intensities and output the data as frequency. A module made by parallax will be used to interface the Taos color sensor with the microcontroller through an A/D channel. The color sensor receives power from a 5V connection.

The module allows the frequency range to be scaled down to a range that the microcontroller can detect, and must be put in a separate mode to detect each color’s intensities. In order to do this, four output pins will be needed to set the scaling and the mode.

For the scaling, the pins on the board can be directly tied to VDC or GND, depending on the scaling that is needed. The two mode control


pins will be controlled by two general purpose I/O pins on the microcontroller.

5.2.7 Power Sources

The battery design is required to be a secondary type, rechargeable, battery, as primary batteries require frequent replacement, and thus would make the vessel very expensive to operate. Furthermore, it is much easier to recharge the batteries in place than to open the entire hull every time batteries needed to be replaced. However, when secondary batteries are used in an application that requires reliability, care must be used to ensure that any battery failure during, or at the onset, of vessel operation is properly sensed and reported to the user.

5.2.5.1 Selection of battery chemistry

The team rapidly realized during the design phase that compared to the first generation SADCATS, power consumption would be much greater, because the second generation vessel is to be propelled with electric motors where the first generation vessel is un-powered. In addition to this, the new vessel also needs to be much lighter than its predecessor, perhaps even light enough for hand-deployment. Naturally, the conclusion is that batteries with higher energy density would help meet these two design goals.

Therefore, the most desirable battery chemistry for the project would offer high gravimetric and volumetric energy density. On top of that, a chemistry that requires simple power management circuitry allows for many charge/recharge cycles, and is easily available at a reasonable cost. Of the many possible chemistries available, discussion here within is limited to the three biggest contenders: Lead-Acid, Nickel Metal-Hydride, and Lithium Ion.

Lead acid was the chemistry choice of the Generation One SACATS project team. Lead-Acid batteries are available for a low cost, and are available in a wide variety of capacities (per cell), making power


delivery simple. This chemistry is also very resistant to overcharging, which simplifies charging of the cells. Additionally, Lead-Acid cells can be found in a large range of capacities, simplifying the construction of a battery pack that has a large energy density. However, the gravimetric energy density, 30 to 50 Watt Hours/Kilogram, is poor compared to the other contenders. Lead-acid cells are not desirable for applications in which a battery is deep discharged, as this damages the cells and shortens the number of charge/discharge cycles of the battery before failure.

Lithium-Ion is a much newer battery technology that allows for very good gravimetric energy density at 110 to 160 Watt Hours/Kilogram, and excellent volumetric energy density. However, Lithium-Ion cells are very expensive per Watt hour, and the Lithium-Ion cells are sensitive to overcharging and discharging at too high a rate, requiring more complex electronics for power management to prevent damage. Lithium-Ion cells are not commonly available in large capacities, meaning that a large-capacity pack requires many cells.

Nickel-Metal Hydride (NiMH) chemistry has been chosen, mainly because of its high gravimetric energy density, ranging from 60 to 120 Watt Hours/Kilogram. This chemistry carries a significant price premium over Lead-Acid, but the increased energy density gives tangible improvements to the weight of the vessel, making deployment easier, decreasing hull material costs, and decreasing drag through the water. NiMH cells are not commonly available in capacities exceeding 9 Watt hours per cell, and the most dense NiMH cells are typical in the area of 5 Watt hours per cell. This means that a large capacity pack requires a high quantity of cells, but a large number of smaller cells provides more options for battery positioning inside the hull.

5.2.5.2Determination of Battery Capacity/ Configuration

A power budget was constructed to compare different battery pack configurations, and to find a solution that provides enough capacity to


meet the target mission length of 16 hours. A good portion of the duty cycle data is a best-guess estimate, and this means that in action, the vessel could use power at a different rate than shown. It is preferable to partition the cells into packs such that an incorrect estimation of the motor's rate of power use would not cause one pack to discharge a long time before another pack. It is also be ideal to provide a way for the microcontroller board, GPS, and radio to remain active even if the power allotted to the drive motors, dive pump and solenoid valve has been used. Thus it was decided that two packs are to be used, a high capacity pack for large current devices, such as the motors, pump, and solenoid valve, and a smaller capacity pack for everything else, including the Microcontroller, GPS, and Radio. This configuration has the added benefit of protecting the Controller Board from the voltage fluctuations caused by switching high current devices on and off.

Table 5.2.2 Vessel Power BudgetPart Voltag

eCurrent, inactive

(mA)

Wattage, inactive

(W)

Current, active (mA

Wattage, active (W)

Dutycycle

Effective (W)

Temp sensor

5 0 0 .300 .002 10% .000

Press sensor

12 00 0 1.500 .018 10% .002

Color sensor

12 0.007 0 2.000 .024 10% .002

Opamps 12 0 0 2.000 .024 100% .024Modem chip

3 8 .024 10.00 .030 1% .024

Turbidity sensor

12 0 0 32.00 .384 10% .038

uContorller

5 12 .06 20.00 .100 100% .100

Radio 12 0 0 1000 12.00 1% .120GPS 5 20 .1 120.0 .600 90% .550Solenoid valve

12 0 0 1220 14.64 5% .732

Pump 12 0 0 8000 96.00 2% 1.920Motors 12 0 0 3000 36.00 50% 18.00


All parts 21.57Pump, motors, solenoid valve

20.65

All other parts

0.837

Based on the Power Budget spreadsheet, it is determined that the Motor Pack have a capacity of around 300Wh, and the Communications Pack should have a capacity of around 20Wh to ensure long communications lifetime and increase reliability.

Table 5.2.3 Battery Capacity OptionsPack 1 battery capacity (Wh)

Pack 2 battery capacity (Wh)

Travel/Dive life (hours)

Communication life (hours)

Option 1 108 21.6 5.23 23.72Option 2 216 10.46Option 3 324 15.69Option 4 (lead-acid) 288 13.95

Table 5.2.4 Battery Capacity Options

cell type/ chemistry voltage

cell capacity (mAh)

pack capacity (Wh)

number of cells

price/cell ($)

Weight per Cell (gram)

Weight per Pack (gram)

Weight per Pack (lbs)

price per pack ($)

Volume (in^3) (as a block)

pack 1, option 1 4/3A NiMH 1.2 4500 108 20 5.75 62 1240 2.728 115 27.3pack 1, option 2 4/3A NiMH 1.2 4500 216 40 5.75 62 2480 5.456 230 54.7pack 1, option 3 4/3A NiMH 1.2 4500 324 60 5.75 62 3720 8.184 345 82pack 1, option 4 Lead Acid 6 12000 288 4 21.8 15.72 87.2 184.7pack 2, option 1 AA NiMH 1.2 1800 21.6 10 2.00 28 280 .616 20pack 2, option 2 Lead Acid 12 2300 27.6 1 12.5 2.05 15 22.4


5.2.5.3 Power Management

A key problem the team encountered in building a high capacity NiMH pack is that capacity must be increased without paralleling cells, which can lead to discharging problems that shorten the life of the cells.

One solution given a lot of consideration was the use of a higher voltage than the standard 12 Volt DC system. For instance, a 36V system would allow for triple the pack capacity than compared with a 12Volt system using the same cells in each case. 36V motors should, theoretically, be lighter than a 12V version for the same power output, because lighter gauge wire can be used for the windings, though in practice the team did not see this advantage while looking for parts. Moreover, pumps, motors, and solenoid valves are generally more available at 12V. 12V components could still be used, but a high current switching regulator would be needed to convert from 36V to 12V, adding to the expense and complexity of the power electronics board and creating a 20% worst-case power loss through the regulator. Still, even if suitable 36V components could be found, the Power Budget shows that the resultant 36V pack would probably still not have the capacity needed, and some sort of other provision (paralleling, separating packs) would be needed to get a high enough capacity.

A simpler method involves putting diodes in series with each pack, which allows packs to be paralleled without any discharge problems. The drawback is that there is a power loss due to the voltage drop across the diode, and high current devices exacerbate this problem. The efficiency for this method could be better than 95% if the right diodes were chosen, and this convinced the team to go with the diode solution.


5.2.5.4 Battery Voltage Sensing, Power Redundancy, Power Switching

Sending a sample of each pack’s voltage to two ADC inputs on the Atmega128 allows the battery pack voltages to be monitored. This in turn allows the microcontroller to ensure that the vessel does not initiate a dive when the Motor pack is depleted. In addition, two power FET's are connected the solenoid valve to allow vessel surfacing using power from the Communications Pack even if the Motor Pack is depleted to the point that its voltage is insufficient to actuate the valve. In this case the vessel is able to make a final surfacing and enter Battery Fail Mode.

5.2.6 Electromechanical Devices

5.2.6.1 Motors

The motors operate for a large portion of the duration of the mission. For this reason, motors with a relatively low current draw are desirable, so as to not drain the capacity of the batteries. From calculations of the power needed to push the vehicle thorough the water at a desirable speed, it was determined that motors should have an input power between 15 and 20W. Since the motors are powered by a 12V connection, the motors should nominally draw 1.25A to1.67A each. Using the power budgeting calculations, and that power range, the vehicle’s motor pack will last from 14 to 18 hours.

Further analysis was conducted in order to find the ideal motor for this application. The motors will need to put out between 6oz-in to 12-oz-in of torque. There are no specific size limitations due to the fact that a casing for the motors has not been developed as of yet. Refer to Appendix (xx) for calculations regarding the actual amount of torque needed for the motors.

5.2.6.2 Pump

As the determination of the battery chemistry was made prior to pump selection, electrically importance was thus placed on the


requirement that the pump use a rate of power that the batteries could support. The chosen pump draws 8A maximum, which translates to 1.33A per battery if the batteries are connected in parallel. This amperage will cause little voltage drop within the battery when configured in this fashion, since batteries of NiMH composition have relatively low internal resistance. 5.2.6.3 Solenoid Valve

Two types of solenoid valve were investigated; normally open and normally closed. The normally open valves were desirable in the case of battery failure underwater. If the batteries fail, the valve would open and the vehicle would surface. However, since investigation determined that normally open valves require higher current to close than normally closed valves would require to open, a software failsafe was designed in order to allow the a normally closed valve to operate if the motor pack were to be depleted.

A normally open valve would require power to remain closed during the enter dive phase, and when stopping to collect data. However, a normally closed valve would only require power when it needs to be opened to rise. As such, the normally open solenoid valve would be active for longer amounts of time, further decreasing battery life.

The selected valve is normally closed and draws .33A when closed.

5.2.7 Lighting

The intent of navigation lights for the vessel is to provide compliance to the United States Coast Guard boating regulations. Aside from regulatory concern, it was important for recreational boaters to be able to distinguish the difference between the vessel and the water surface.

The total vessel length is less than 48 inches and thus the Coast Guard Regulations designate motor-powered vessels under 12 feet in length to have a light on the bow with a green and red light. Each light on the bow must be visible from 120-degrees. There is also a


requirement for a stern light which is white. The white light must be visible for 360-degrees. The driving principle of the lighting configuration is to allow for nocturnal boaters to decipher the direction of waterway traffic. The table below correlates the direction of travel with the light that is visible from the boat.

Table 5.1.XLighting Visible Direction of Travel for

Vesselwhite light away from observer

green light and white light rightred light and white light left

red and green light toward observer

Another variable that had to be considered was the estimated speed of the vessel. The group planned the speed of the vessel with respect to the maximum foreseeable current it would experience on Lake Ontario during typically weather patterns. As the max current was estimated to be one-half of a knot, the design team planned the vessel to have surface mobility at a speed of 1 knot, which translates to 1.15 mph.

It was determined that the U.S. law was questionable on the point of lighting for a powered autonomous craft. The SADCATS project vessel does not fit the United States Coast Guard's definition of a “vessel”, because it is autonomous. On the other hand, the team's vessel is not just a buoy, as buoys are defined as moored or drifting, while the SADCATS vessel is powered. The U.S. Coast Guard Inland Navigation Rules are not clear on the requirements for such a vessel and no clarification was given when the Coast Guard was contacted.

The design team attempted to find components to achieve the United States Coast Guard boating regulations. Mounting lights on the outer surface of the vessel was not a feasible option and available lighting


did not meet the pressure specifications that would be needed for diving to 100ft. Lights mounted on the outside of the vessel would also create more drag.

The vessel is predicted to have a mission length of 16 hours and thus could be deployed at the beginning of the day and retrieved in the evening. Therefore its operational period would typically take place in daylight.

Nevertheless, if the vessel is to run between sunset and sunrise, it must have some lighting, even if it is lighted as if it was a drifting buoy. Installation of a mast head light on the exterior of the vessel was found to be problematic for the mechanical design due to stability, sealing, and drag concerns. The team has decided instead to opt for a daytime mission profile, so that the vessel will not require lighting, but will instead feature a florescent orange flag on the antenna mast and the hull will be outfitted for high visibility. The design will be kept flexible to allow possible future installation of a buoy caution light on the exterior of the vessel, or the installation of a 180-degree visible blinking light inside the transparent front hemisphere of the craft.

When the group weighed all the factors, it was talked about to put a white light in the hemisphere section of the sub. Since the sub will run day missions, it is not critical for it to have a white light. A white LED during the day doesn’t serve a great deal of purpose. By containing the light inside the sub, it would not be subjected to external pressures caused by the water depth. The hemisphere will be made of plexiglass which is transparent. The light would be visible from inside the hull. During the course of our information search, a correlation was found to relate candle power of an LED with a distance of visibility. The LED(s) we have picked provide for a visibility of up to 6 nautical miles.

Table XXX (refer to reference XXXRange of visibility

(luminous range) of Minimum luminous intensity of light in


light in nautical miles candelas for K = 0.811 0.92 4.33 124 275 526 94

However, at this point in time we do not know how well the plexiglass will allow light to pass through. Testing would need to be done following assembly to be sure of the visibility distance provided by the LED(s) from inside the hull.

Another possible implementation to make the sub more visible is to apply reflective tape to the cylindrical sections of the hull. This would make the sub highly visible during daylight hours or in the proximity of other the navigation lights of other vessels.

5.3 Analytical Conclusion

The design of the electrical systems allow the vessel to make accurate scientific measurements more easily than the present “bucket” practice. The craft is able to navigate to waypoints autonomously via utilization of GPS telemetry and transmission of acquired data to base station for analysis.

Power redundancy decreases the chance of losing the vessel to sea or to the bottom of a lake. A system status LED alerts the user to any error conditions prior to deployment, and verifies proper operating status. Power management is efficient and the battery has proper capacity to complete the misson.

There are some unresolved issues, however. Integrity of the transmitted data must be ensured either by uni-directional or bi-


directional error detection and correction protocols. Additionally, a copy of the data should be logged locally so that it can be downloaded after the vessel is retrieved. Motors and propellers also need to be determined. Calculations have been made that can determine the correct motor and the correct propeller. As of now, the team is waiting for a response from the motor vender on what the most suitable motor will be for our situation. After that is taken care of, propellers can be sized accordingly.


6.0Status and Outlook

With the conclusion of the Preliminary Design Phase of the Sr. Design Project, the SADCATS group now looks forward to the transition from the design phase to the fabrication and testing phase.

6.1 Obtainment of Components and Materials

Purchase requests have been turned in for all of the components and materials. The bill of materials can be found in section 6.4 under Budget. As for the motors and propellers, exact models are still to be determined. Their respective prices and vendors have been left out for the time being.

6.2 Fabrication

The fabrication of the frustrum and hemisphere for the hull of the sub is to be made by Quickturn modeling. The cylinder section will be fabricated by the team. The rest of the construction, including the integration of the electrical components will be completed in the next ten weeks. The microcontroller board schematic is being jointly developed under Dr. Kremens, the sponsor. The board layout, board manufacture, and component stuffing will be performed by FSI systems, Farmington NY.

6.3 Testing and Calibration

6.3.1 Temperature Sensor Calibration

The temperature circuit will be calibrated to provide 10mV/K before

amplification and shifting. This should be done using a potentiometer to calibrate

the circuit with the proper resistance value. Since the range of interest is from 0°C

to 32°C, the circuit will be shifted by some bias voltage which will be

provided using a calibrate voltage divider that uses a potentiometer.

6.3.2 Pressure Sensor Testing and Calibration

The zero point offset of the pressure sensor will be measured by measuring the

atmospheric voltage compared to a known current value and interpolating the data


back to the zero to measure the offset. If the offset is non-zero, it will be

compensated via software.

6.3.3 Dive and Surfacing System Testing

Testing the dive system will be accomplished by setting the software to only

include the dive system. The vehicle will be placed in a deep swimming pool or

other large body of contained water. A short dive depth will be specified in order to

determine whether the system can properly dive and surface in a body of water in

which it can easily be retrieved should the system fail to either dive or rise.

6.3.4 Locomotion Control Testing

The craft will be tested on an open body of water in order to determine if the craft

will adequately be controlled on the surface. Starting from a random bearing, the

craft will be required to accurately seek the waypoint within a minimum error

distance to be determined. This test will be performed independently of the dive

and surface phases of the code.

6.4 Budget

The budget for SADCATS is shown below. Bill of Materials

Item Part Name

Part Number

Material

Vendor Quantity

Price ($)

Line Price ($)

Ballast System Pipe Fitting

9171K22 Brass McMaster-Carr

2 7.09 14.18


3 1.84 5.52

InlineStrainer


1 11.58 11.58

Tube Fitting

44555K132

Brass McMaster-Carr

3 1.38 4.14

Solenoid Valve

7876K11 Delrin / nitrile

McMaster-Carr

1 34.38 34.38

Air Tank Valve


2 2.80 5.60

Check Valve


1 8.17 8.17


1 8.17 8.17


Tubing 5394K16 Nitrile / Nylon

McMaster-Carr

10 .92 9.20

Hose Clamps

54195K14 Stainless Steel

McMaster-Carr

1 4.47 4.47

Dromedary Bag

87707 Cordura Nylon

Campmor 1 24.95 24.95

Dromedary Bag Cap

601650 Plastic REI 1 10.00 10.00

Pump 61957 Advanced Auto

1 154.14 154.14

Electromechanical

Motor Faulhaber 2 TBD

Hull Cylinder 48855K52 PVC McMaster-Carr

1 63.60 63.60

Frustrum Quickturn 6 45.00 270.00Hemisphere

Quickturn 3 45.00 135.00

ABS block ABS Quickturn 1 TBD TBDPlexiglass block

Plexi-glass

Quickturn 1 TBD TBD

Supports 8747K128 PVC McMaster-Carr

1 18.08 18.08

Mechanical Propeller 2 TBDMiscellaneous Teflon

Tape4591K12 PTFE

TeflonMcMaster-

Carr1 1.59 1.59

O-rings 9557K201 EPDM McMaster-Carr

2 6.67 13.34

The electric components will be covered under the College of Imaging Science

Estimated Cost = $796.11

Electrical Power Amplifier

RA07H4047M

RFparts.com

1 19.75 19.75

Batteries MhDBA1700TAB

Thomas 10 2.65 26.50

GPS GPS35-HVS

Purchased by

sponsor

1 0.00 0.00

Temp Sensor

28138 Parallax 1 9.00 9.00

Color sensor kit

30054 Parallax 1 79.00 79.00

Diode 177973 Jameco 10 .73 7.30MOSFET 210518 Jameco 10 .25 2.50Relay kit RFS1 Ramesy

Electonics1 19.95 19.95

Estimated Cost = $164.00

6.5 Project Completion Timeline

The project completion timeline can be found overleaf.


6.6 Unresolved issues

6.6.1 Mechanical

6.6.1.1 Motors Although calculations have been made in order to select motors for

the vessel, the vendor is in the process of selecting the best motor for the mechanical and electrical requirements.

6.6.1.2 Propellers In order to select the propellers, the motor selection is needed first.

Thedimensions of the propellers can somewhat make up for a lack of torque from the motor.

6.6.2 Electrical

6.6.2.1 Recharging Cables

Among the electrical issues still remaining is the issue of recharging the batteries. Currently there is no simple way to recharge the cells. While it would be possible to remove the end cap and access a charging cable in that manner, this is hardly ideal. Possible solutions include a watertight plug that could allow access to the charging apparatus, or some sort of inductive charger. Currently there is no way to bring out a charging cable, however charging equipment has been obtained.

6.6.2.2 Power Switch

Also undressed is a method of powering on and off the craft. Similar to the issue of recharging methods, it would be beneficial to have some


external means of switching the power on and off. Possible methods include a sealed plug that would be attached to the wires connected to the power switch. The power switch could be fastened to the underside of the plug. If it were difficult to fasten wires to a plug, they should be easily accessible using a pair of tongs or my reaching in with a hand.

6.6.2.3 Software Revisions

It had been desirable to be able to reprogram the microcontroller via radio, however since the ATmega128 receives code through a JTAG interface, this is no longer possible. Concurrent with the power switch and recharging mechanisms it would be desirable to have a means of revising software without removing the end cap.

6.6.2.4 Control System Parameters

Due to lengthy mechanical systems analysis, there had been insufficient time to simulation and design for the exact control system parameters. A PI controller had been designated for locomotive control on the surface, while simple on/off control methods had been specified for the controlling the pump and solenoid valve. The next step is to develop a working simulation in which the control system parameters can be designed and developed by integrating the mechanical design equations into a MatLab simulation alongside a model of the control system.

6.6.2.5 Waypoint Determination

A method of waypoint determination is currently undecided. Some possibilities are for the craft to use its initial position as the first waypoint, and calculate other waypoints relative to that location. The waypoints may spiral outward from the initial position, move in a zigzag pattern from west to east, or any other scheme that would allow for a suitable grid of data to be collected.


7.0Conclusion The presented design provides a solution that will be invaluable to the client. The vessel

is much lighter weight, has horizontal locomotion ability, and also boasts the addition of

turbidity, conductivity, and water color sensing. The second generation design still

retains the features of the first generation vessel, namely diving ability and GPS

awareness.

There have been some bottlenecks in the design. The first priority of the electrical

designers will be to finalize the microcontroller board schematic allow prompt testing of

sensors and programming. The mechanical designers will acquire the motors and

propellers to allow fabrication of the motor housing.


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Appendix

A.1 Initial Concept Development IdeasA.2 Weighting of Criteria for AnalysisA.3 Concept Feasibility Voting Results A.4

B Psuedocode for ControllerB.1 Psuedocode for Initialization PhaseB.2 Psuedocode for Waypoint Seek Phase B.3 Psuedocode for Dive Cycle Phase B.4 Psuedocode for Rise Cycle B.5 Psuedocode for Data TransmissionB.6 Psuedocode for Battery Fail

C Flow Chart for ControllerC.0 Flow Chart of Entire SystemC.1 Flow Chart for Initialization PhaseC.2 Flow Chart for Waypoint Seek Phase C.3 Flow Chart for Dive Cycle Phase C.4 Flow Chart for Rise Cycle C.5 Flow Chart for Data TransmissionC.6 Flow Chart for Battery Fail


A.1 Initial Concept Development Ideas

01. Gas powered boat02. Sailing surface vehicle03. Buoy that takes measurements04. Submersible with electric motors05. Pontoon boat06. Solar Buoy07. Solar Boat08. Surface vehicle with sensors on a tether09. Submersible with snorkel to transmit data10. Dynamic diver11. Static diver12. Hybrid diver13. Drifter without powered directional control14. Open frame submersible15. Closed frame submersible16. Surface vehicle with electric motors17. Cluster of transmitting and receiving pods18. Electric surface vessel with programmed diving19. Closed frame boat20. Drifter powered by solar cells


A.2 Weighting of Criteria for Analysis

Wei

ght

Cost

Relia

bilit

y

Adap

tabi

lity

Diffi

cult

y

Part

Ava

ilabi

lity

Life

Spa

n

Pack

age

Serv

icea

bilt

iy

Com

mun

icat

ions

Pow

er

Cons

umpt

ion

Capa

bilit

y

Weights

Weight 5 0.07576Cost 3 0.04545

Reliability 7.5 0.14394

Adaptability 2.5 0.06818

Difficulty 2.5 0.06818

Part Availability 2.5 0.09091

Life Span 1.5 0.05303

Package 1 0.06061Serviceability 1 0.05303Communications 2 0.15152Power Consumption

0.5 0.07576

Capability 0 0.113640 0 2 2 2 3.

5 2 3 2.5 8 4.

57.5 1.00000

Favors Row Split Decision Favors Column


A.3 Concept Feasibility Voting Results

Pugh's Method with Weighted Scale

Base Model: Electric Surface Vessel

Electric Submersibl

e

Solar Surfac

e Weight

sWeight 1 3 0.07576Cost 2 2 0.04545Reliability 3 3 0.14394Adaptability 4 2 0.06818Difficulty 1 2 0.06818Part Availability 3 3 0.09091Life Span 2 3 0.05303Package 4 2 0.06061Serviceability 2 3 0.05303Communications 3 3 0.15152Power Consumption 2 4 0.07576Capability 5 3 0.11364

Comparative Score 2.840912.8333

3 1.00000

A score of 3 is equal to base line, with 5 best, 1 worst

A.4


B Psuedocode for ControllerB.1 Psuedocode for Initialization Phase

Psuedocode for Initialization Phase

read: battery voltage from the motor pack (A/D, Port F)read: battery voltage from the communication pack (A/D, Port F)

if (motor pack voltage too low OR communications pack too low)while (vehicle is on)

if (motor pack voltage is too low)flash: red LED for 3 flashes (General I/O Pin)pause

end

if (communications pack voltage is too low)flash: red LED for 2 flashes (General I/O Pin)pause

endend

/* All systems go */set: integral error to zeroflash: red LED continuous for 3 seconds

delay: 3 minutes until exiting initialization

check: if GPS has initialized properly (General I/O Pin, Virtual Serial)

while (GPS not initialized)NOP

end


B.2 Psuedocode for Waypoint Seek Phase (Perform algorithm every sec)

check: if GPS has initialized properly (General I/O Pin, Virtual Serial)

while (GPS not initialized)NOP

end

read: GPS string from I/O pin (virtual serial, port).fetch: current position, (x,y) from the GPS string

Δx=xcurrent-xprevious

Δy=ycurrent-yprevious

xerr=xwaypoint-xcurrent

yerr=ywaypoint-ycurrent

θerr=(Δx*xerr+Δy*yerr)/( (Δx2+Δy2)1/2 *(xerr2+yerr

2)1/2 )mΔ=Δy/Δxmerr=yerr/xerr

PE = Kp*θerr /* Kp is %/˚ */

if [ (|mΔ|>|merr|) AND Δy>0 ] OR [ (|mΔ|<|merr|) AND Δx<0 ] /*Means angle is 0 to 180˚*/IE = Ki*θerr+IELeft motor gets 100%Right motor gets 100% - (PE+IE)

else/*Means angle is 0 to -180˚*/IE = Ki*-θerr+IERight motor gets 100%Left motor gets 100% - (PE+IE)

end

if (left motor power less than minimum motor power)set: left motor power to minimum power

endif (right motor power less than minimum motor power)

set: right motor power to minimum powerend

set: left motor PWM to the set percentage (Port B, one of [7..4])set: right motor PWM to the set percentage (Port B, one of [7..4])

save: current position, (x,y) to memory for next waypoint seek calculation

read: battery voltage from the motor pack (A/D, Port F)

if (battery voltage is too low)call: the battery fail function

end

Δs=(xerr2+yerr

2)1/2

if (Δs < Δsmin)/* Sub is within range of waypoint*/


set: left motor PWM: 0% (Port B, one of [7..4])set: right motor PWM: 0% (Port B, one of [7..4])set: integral error to zero

end

B.3 Psuedocode for Dive Cycle Phase (Loop performs every sample interval)

Apply Voltage to pump

read: pressure from sensor (A/D, Port F)

while (pressure < Pmax)read: battery voltage from the motor pack (A/D, Port F)

if (battery voltage is too low)turn off pumpdo

open solenoid valve (General I/O Pin)while( not on surface)

call: the battery fail functionend

read: pressure from sensor (A/D, Port F)end

read: pressure sensor (A/D, Port F)

while (below depth for first data point)open solenoid valve (General I/O Pin)

end


B.4 Psuedocode for Rise Cycle (Loop performs every sample interval)

next data point depth = 100ft

while (depth > 1 ft)save: coordinatesread: pressure (A/D, Port F)save: depth/pressureread: temperature (A/D, Port F)save: temperaturesend: data request to turbitidy sensor (General I/O Pin)read: turbidity (General I/O Pin)read: conductivity (General I/O Pin)save: turbiditysave: conductivityset: color sensor: red mode (2 General I/O Pin)read: red intensity (A/D, Port F)set: color sensor: blue mode (2 General I/O Pin)read: blue intensity (A/D, Port F)set: color sensor: green mode (2 General I/O Pin)read: green intensity (A/D, Port F)set: color sensor: white mode (2 General I/O Pin)read: white intensity (A/D, Port F)

read: battery voltage from the motor pack (A/D, Port F)

if (battery voltage is too low)switch solenoid valve to controller battery packdo

open solenoid valve (General I/O Pin)while( not on surface)

call: the battery fail functionend

while (depth < depth for next data point)open solenoid valve (General I/O Pin)read: pressure (A/D, Port F)

end

next data point depth = current data point depth + 1ftend

open solenoid valve (General I/O Pin) /*empty ballast*/


B.5 Psuedocode for Data Transmission

enable: transmit (General I/O Pin)while (Δt < .1sec)

NOOPend

transmit: data (tx serial, UART 1, Port D)

while (Δt < Δtmax)read: rx serial, UART 1, Port Dif (transmission acknowledged)

returnendNOOP

end

enable: transmit (General I/O Pin)while (Δt < .1sec)

NOOPend

transmit: data (tx serial, UART 1, Port D)

while (Δt < Δtmax)read: rx serial, UART 1, Port Dif (transmission acknowledged)

returnendNOOP

end

save: transmission not ack’d status

B.6 Psuedocode for Battery Fail (repeats every second)

while (vehicle has power)read: GPS (General I/O Pin, Virtual Serial)fetch: coordinates from GPS string

enable: transmitwhile (Δt < .1sec)

NOOPend

transmit: location (tx serial)end


C Flow Chart for Controller

C.0 Flow Chart of Entire System

C.1 Flow Chart for Initialization Phase


C.2 Flow Chart for Waypoint Seek Phase


C.3 Flow Chart for Dive Cycle Phase

C.4 Flow Chart for Rise Cycle


C.5 Flow Chart for Data Transmission

C.6 Flow Chart for Battery Fail


D Results of Finite Element AnalysisD.1 Displacement Due to 165 (Expected +30)psi Internal Ballast System Load

D.2 Von Mises Stress Due to 165 (Expected +30)psi Internal Ballast System Load


D.3 Strain Due to 90 (Expected +30)psi External Vessel

D.4 Von Mises Stress Due to 90 (Expected +30)psi External Vessel Load


D.5 Displacement Due to Maximum External and Internal Pressure Loads

D.6 Von Mises Stress Due to Maximum External and Internal Pressure Loads



Documents

SADCATS Preliminary Design Report - Rochester …edge.rit.edu/content/P04034/public/PDR.doc · Web viewSubmersible Autonomous Data Collection and Transmission System (S.A.D.C.A.T.S.)