RockSat 2010 Final Report Template

Temple University 7/18/2011

RockSat-C 2011

RockSat-C 2011 Final Report

Team SAVSS

Our mission has been, to design, build and integrate an active vibration damping system

to alleviate vibration in the z-direction during the coast phase of the rocket flight. This

has been done utilizing piezoelectric materials.

Students: Donovan Bolger, Xuhui Liu, Greg Wells, John Zebley

Advisor: Dr. John Helferty

Temple University

7/18/2011


RockSat-C 2011

1.0 Mission Statement

Space exploration defines the current human era in anthropological terms. The

understanding of space and the uses of space for advancement on Earth have

summed up the technological advancements achieved over the last fifty years.

Besides the benefit of understanding distant galaxies and solar dynamics through

use of reconnaissance spacecrafts, space exploration has yielded an unprecedented

understanding of Earth sciences. One major factor of inhibition to the success of

scientific research performed throughout and past Earth‟s atmosphere is the

instability of the experiment‟s transporting vehicle. Sounding rockets are typical

vessels used for low earth-orbit experimentation. These rockets tend to experience

vibrations in the x, y and z-axes as well as detrimental forces of up to 25 G‟s. Due

to these vibrations and high G forces, many possibilities for useful scientific

research are prevented because they would not be able to withstand the instability

of the rocket. The stabilization of sounding rockets intended for transporting

research experimentation would offer scientists the opportunity to design and

implement fragile equipment which would otherwise be liable to fail under the

stress of serious vibrations.

2.0 Mission Requirements and Description

In order for the mission to be considered a success, the Sub-Orbital Active

Vibration Suppression System must meet stringent constraints. Listed below are

the functional and non-functional constraints. Because of the severity of the

constraints, there is little margin of error.

The five functional design constraints are shown in Table 2.1. In compliance with

the NASA RockSat user guide, the SAVSS must provide its own electrical power

for the payload. To work with the strict weight restrictions defined by the RockSat

program, two rechargeable 9V DC batteries will be utilized to supply sufficient

power to the microcontroller unit for the rocket‟s anticipated flight-time of 1000

seconds. Rechargeable lithium ion batteries will not be used as they are strictly

prohibited aboard the Terrier-Orion Sounding Rocket.

The majority of the system and its sub-systems can operated at voltages under

18V. However, the damper components will require a range of voltages from -100

to +400V. This forces the SAVSS to amplify the 18V DC to meet the proper

power requirements of the dampers so that their piezoelectric properties can

function properly.

The vibrations SAVSS aims to suppress are those that propagate randomly in the

high and low frequency range through the z-axis of the rocket. Our system must

be able to recognize and convert these vibrations from an analog to digital signal.

The vibrations will be detected by 4 accelerometers: two high range z-axis and

two low range z-axis accelerometers. Two sets of the same z-axis accelerometers

must be used in order to compare the accelerations of the non-fixed


RockSat-C 2011

to that of the fixed plate. The accelerometers will output an analog voltage signal.

To store this signal into memory, the MCU must convert the analog voltage to a

10-bit form. The data will be stored at 1MSPS to ensure that sufficient data is

recovered during the flight.

Based off of the RockSat Wallops Environment Test, SAVSS will concentrate on

a range of vibrations from 0-144Hz. This is the lower end of the vibration

frequencies the rocket will experience. The higher accelerations from the initial

thrust of each stage of the rocket are impulses. This payload will aim to dampen

vibrations with a 5 to 1 damping ratio utilizing an active-vibration suppression

system.

The entire duration of the flight is approximately 15mins. During this flight the

payload will experience many random high and low frequency vibrations. To

ensure SAVSS obtains a sampling rate fast enough to capture all vibrations, the

analog-to-digital converter must store our data at 1 MSPS. At this rate, sufficient

data storage space is required. This sampling rate requires storage capacity of 10

GB.

The non-functional design constraints can be found in Table 2. In order to

conform to the ABET handbook on accrediting engineering programs, five

separate constraints dealing with societal issues such as: economical,

environmental, health and safety, manufacturability and sustainability.

Working with an overall budget of $2,000, the piezoelectric dampers must be

affordable enough to purchase and still have enough capital for all other parts.

Name Description

Power Supply Batteries must be able to supply the system for 1000

seconds

Data Recognition

4-Channel analog-to-digital converter must switch through

all four accelerometers, convert the analog voltage to a 10-

bit form, and store into memory at 4 thousand samples-

per-second.

Vibration Damper

Active vibration suppression system must be able to

achieve at least a 5 to 1 damping ratio of frequencies under

144 Hz

Memory Memory must be vast enough to store 1.5 megabytes of

data

High Voltage DC/DC converter must convert +/- 9V to + 300V and -

300V, for the patch-driving amplification circuit

System Activation Zero currents may flow before the payload experiences 1

G of force in the positive z-axis

Table 2.1: Functional Design Constraints


RockSat-C 2011

The RockSat User Guide, designed in accordance to NASA and the RockSat

program, placed every payload under pre-existing environmental and health and

safety constraints. For instance, the use of rechargeable lithium-ion batteries is

forbidden on the rocket as to protect all payloads. SAVSS must keep the total

current in the RockSat activation line below 750mA. The system must also

conform to the values of internal pressure, temperature and spin rate set defined

by Wallops Flight Facility.

The system must be sustainable and must operate at a certain rigidity and

robustness in order for mission success. The design of the system requires that it

will survive underwater after it splashes into the ocean. The entire system must

also be rigid enough so that it can withstand periods of forces ranging up to 20

G‟s in the Z, or thrust, axis. The entire design must also conform to the RockSat

user guide in the line of its weight, size and center of gravity. The system, as well

as all others on board, must lie within a 1 x 1 x 1 inch envelope in order to

guarantee a spin-stable rocket. The system must also weigh no more than 6 lbs

and must fit in a cylindrical canister, 9.3” in diameter and 4.75” in height.

Type Name Description

Economic Cost Entire budget must be under $2000

Environmental

Saftey

May not use rechargeable or lithium-ion

batteries or wireless communications. Each

could potentially harm or create noise

interference to other payloads or the rocket

itself

Durability

Flight Survival

This system will be designed to operate over a

6-minute flight; experience up to 25 G‟s and

operate in the event of the canister becoming

wet at splashdown

Physical

Volume/Weight/CG

In accordance with RockSat constraints, the

payload canister is limited to 9.3” in diameter,

4.75” in height and 10 lbs in weight. The center

of gravity of the canister has to lie within a

1 inch envelope.

Manufacturability

Launch Date

Must have demonstrated full functionality,

passed all structural and environmental testing,

and be fully assembled and integrated by

6/23/1011

Table 2.2: Non-Functional Design Constraints


RockSat-C 2011

Figure 1: Payload Canister

3.0 Payload Design

In order to effectively explain the active vibration suppression system in its

entirety, it has been broken it down into sub-systems. A full system block diagram is

found in Figure 2 (following page.) Although each sub-system listed in the block diagram

will be explained in depth in later sections, a short overview of the entire vibration

suppression system is first given for comprehension.

The entire system must fit into a cylindrical space of 4.75” in height and 9.3” in diameter,

exactly one half of the canister shown in Figure 1. The system has been powered with 2

rechargeable 9V batteries. To meet requirements placed upon all payloads by NASA and

the RockSat program, the system was to be unpowered until time of launch. This

requirement was met by incorporating a G-switch into the system, which allows power to

flow once acceleration is experienced at the time of launch. Although power was supplied

throughout the system at the instant of launch, vibration suppression did not begin until

after the 2nd

burn of the sounding rocket. The PIC32 microprocessor began its control of

the piezoceramic DuraAct Patches after the 2nd

rocket burn to ensure that the rocket was

in its coast phase. This was done because the aim of this project was not to suppress all

vibrations experienced throughout the flight, but rather the vibrations of lower

frequencies experienced during coast phases, apogee and parachute deployment. The

frequency range in question was 0 to 144Hz, which

are the exact values used to test all payloads flying in

the RockSat program for stability prior to launch.

As the rocket experienced these vibrations,

accelerometers sitting on both the rigid and floating

plates were continuously reading and writing analog

voltages to the PIC32. The PIC32 has an internal

Analog to Digital Converter (ADC) which converted

and stored the incoming analog voltages in memory.

The ADC was 4-channel to deal with the 4

accelerometers, and sampled at forty thousand

samples per second. These values were continuously

compared and used to control the DuraAct Patches,

which fluctuated in tandem with the current vibration

frequency so as to stabilize the floating platform. The

DuraAct Patches accepted analog voltages ranging

from -100V to 400V. Analysis of the functionality of the system occurred post-flight

once the payload had been retrieved. Data from the PIC32 was loaded into a computer

which allowed for a comparison of the vibrations experienced on the rigid plates to that

of the floating plates. An official report will be written as to portray how well the active

vibration suppression system functioned during the 15 minute flight of a sounding rocket

to heights of 72 miles above sea level. A damping ratio of 5 to 1 between the floating and

damped plates was the main goal of this project.


RockSat-C 2011

Figure 4: Comparison of Rigid to Damped Plate Vibration

3.1 Control Theory Found in Figure 3 is a block diagram of the basic control theory used to control the

piezoceramic DuraAct Patches. The patches were directly controlled by the

accelerometers. The accelerometers were placed along the z-axis, faced in opposite

directions. The difference of their values was met with a proportional gain so as to meet

maximum displacement over the range of forces the canister experienced.

After the differences of the accelerometers‟ values were taken, they were sent through an

Figure 2: System Block Diagram

Figure 3: Control Theory Block Diagram


RockSat-C 2011

inverting amplifier that had a gain of 20 V/V. These inverting amplifiers had a voltage

output range of +/- 200 V. By using two of these amplifiers, the piezoelectric patches

were able to experience voltages of up to 400 V. The expected result of the rigid to

damped platform vibration can be seen in Figure 4.

3.1.1 Accelerometer Output

The accelerometers placed on both the rigid and floating plates of the payload were a

crucial part of the design of the overall system. There were two accelerometers on each

plate: one High G and one Low G. Each accelerometer gives an output of 2.5V (+ or –

1V) for every 1 G-force experienced by the rocket. For instance, if the rocket was

experiencing 0 G-forces, the accelerometers would output 2.5V. If the rocket was

experiencing a +1 or -1 G-force, the output of the accelerometers would be 3.5V or 1.5V,

respectively.

3.1.1 Amplifiers

The two differential amplifiers simply take the difference of the two accelerometers.

Since the actual blocking force of the dampers was unknown until final integration, an

adjustable potentiometer was placed so that the ratio of the resistance could enable exact

calibration prior to flight and can be seen in Figure 5Error! Reference source not

found.. Found below in Figure 6Error! Reference source not found. is the expected

blocking force capabilities versus external force that the rocket is expected to experience.

Biased at +/- 300V, the high gain amplifiers invert the output of the differential

amplifiers and give them a gain of 20 V/V. This stage of amplification uses a LF441CH

operational amplifier to control a set of five bipolar junction transistors that are rated for

+/- 300 V. The feedback resistors determined the gain of this circuit. A DC/DC

converter provided by American Power Design converts +/- 9.6 V into +/- 300 V at a

maximum current of 3.96 A. This schematic can be found in Figure 7.

Figure 6: Expected Blocking Force

Figure 5: Adjustable Gain Amplifier


RockSat-C 2011

3.1.5 DuraAct Patches

As each of the four DuraAct Patches received signals from the amplifiers, they expanded

and contracted continuously as to alleviate the

present experienced vibrations. As previously

stated, the patches were set to an initial position

of 25mm each. The patches above and below the

floating platform essentially moved up and

down, relative to each other, at the same

frequency of the present vibrations about the

payload. This allowed for stability of the center,

floating platform. In order to prevent

depolarization of the patches, diodes were

placed between their leads and the amplifiers.

The schematic of these diodes can be seen in

Figure 8.

3.2 DuraAct Patches: A Closer Look The main objective of this design was to

actively suppress a specific range of vibrations.

The problem that arose in this case was the

restriction on the payload space the vibration

suppression system had to work with and the

weight it could budget. With only about 4.75in

of height and a diameter of 9.3in, the payload

space this payload had to work with was very

small. Because of the knowledge of this small

space SAVSS was able to quickly rule out

Figure 9: DuraAct Patch Transducer

.

Figure 7: Main Amplification Circuit

Figure 8: Diode Schematic


RockSat-C 2011

many different options for a vibration damper device.

After some research, SAVSS implemented piezoelectric technology as the damper for its

design. The phrase piezo comes from the Greek word for pressure. Piezoelectronics are

used almost everywhere today; from headphones to insulin injectors for a diabetic the

uses for piezoelectric technology are endless. The particular piezoelectric device SAVSS

utilized in its design was the DuraAct Patch Transducer P-876.A12 provided by Physik

Instrumente (PI). As seen in Error! Reference source not found., the DuraAct Patch

Transducer is incredibly thin, flexible, and compact. The DuraAct has the ability to attach

to non-uniform surfaces and suppress vibration from 1Hz all the way into the kHz range.

By applying a specific voltage to the electric connectors of the DuraAct seen in , the

patch can react by changing its bending radius. The DuraAct works similar to a capacitor;

the flexible ceramic plates inside the DuraAct acts like a dielectric between its metal

surfaces. When a voltage is applied to the connectors in Error! Reference source not

found., an electric field is created inside the DuraAct. This field causes a uniform lateral

contraction of the ceramic plates perpendicular to the direction of the electric field. The

strength of the electric field determines the magnitude of lateral contraction. This

particular behavior is called the transverse piezoelectric effect and can be seen in Error!

Reference source not found. The lateral contraction property of the DuraAct is what allows us to suppress vibrations.

By utilizing the reverse analog signal outputted by our accelerometers, the DuraAct can

use this signal as its power input to effectively suppress the incoming vibration by

physically working against the vibration in the opposite manner. Because the DuraAct

will consume power within a range of -100 to +400 volts at a max current of 25mA, our

design feeds the DuraAct‟s input signal through a model F04 F Series DC to HV DC

converter before inputting that signal to the DuraAct. The F04 DC to HV DC converter

provides a voltage gain of 33.33. The electric power signal is sent to the electric

connectors of the DuraAct patches through two 18 gauge high voltage lead wires which

are insulated to withstand 5-50kV DC and a temperature range of 150-200degrees

Celsius. For SAVSS‟ design, four DuraAct Patch Transducers have been implemented.

Two DuraAct Patches lie on the bottom of the payload supporting the lower floating plate

and a duplicate pair of DuraAct Patches is then placed on the upper portion of the floating

plates. With this layout, the DurAct Patch Transducers will work almost like an active

cushion suspension on either side of our payload system we wish to suppress vibrations

within. Since the DuraAct patches are very smooth on either side, each patch was adhered

Figure 11: Transverse Piezoelectric Effect

Figure 10: Closer Look at the DuraAct Patch


RockSat-C 2011

to a thin square of plexi glass which will act as both a ridged mount to prevent the patch

from moving around to an unwanted position; also the plexi glass will act as a base for

the patch to act against. The adhesive used to mount the patches is HBM Z70

cyanoacrylate glue formulated for mounting strain gages. A model of this layout can be

seen in the mechanical section of this document. Since the correlation between voltage

and displacement is not linear, our design has be calibrated to allow the DuraAct to

receive a signal linear to the reverse of the accelerometers analog output.

3.3 Power System In accordance to the NASA RockSat user guide, no electrical

power shall flow through the payload before the Sounding

rocket has launched. This will be insured utilizing two methods;

one provided by our team and one provided by the RockSat

program. NASA RockSat will have the initial control over the

power source using their RBF (Remove Before Flight) wiring as

seen in Figure 12. The NASA RBF wire is nothing more than an

on off switch to our power source. This gives NASA RockSat

the knowledge that the payload power supplies are not supplying

power before the launch so that they can insure each payload

meets the user guide requirement. Once the RBF wire is

removed and the rocket launches, the second method provided

by our team can initiate to allow power to flow to the system.

The second method is a g-switch integrated into our design. The

g-switch will close from the force of the rocket taking off. Once

the g-switch closes, power from 9V DC rechargeable batteries

will flow into an activation circuit as shown in the diagram of

Figure 13. The 9V DC batteries will be able to provide electrical

power to the entire system for the duration of the flight which is

approximately 15 minutes.

The activation circuit displayed in Figure 13is necessary in

maintaining proper electrical power input to the main system of

the payload. The sounding rocket will not be traveling with

constant

acceleration

especially once the

parachute deploys

after apogee.

Because of this, the

design cannot

guarantee the g-

switch will continue

to stay closed. To

counter this

Figure 12: Stacked

Payloads with RBF wiring

Figure 13: Simulated Activation Schematic


RockSat-C 2011

complication, the activation circuit is comprised of a power latch that has the ability to

hold and maintain a specific voltage value to which our system demands. The output

from the activation circuit will then be regulated and sent to the specific sub-systems of

the design. Power will be provided to the PIC32 expansion board and the DuraAct

patches. Since the PIC32 expansion board can accept an input power range of +9-15V

DC to allow proper functionality of the system, the

output voltage from the activation circuit to the

expansion board was then regulated to 12V DC which

falls somewhere in the middle range. The PIC32

expansion board contains integrated power regulators to

supply the PIC32 board and Memory board with proper

electrical power. The PIC32 board, expansion board,

and memory board can all be looked at as one

component of the system since they were pre-

manufactured by MicroChip Inc.

The PIC32 subsystem not only allows us to sample and

store information, but it also acts as a voltage output for

our vibration suppression components. The output

signal from the PIC32 is a digital signal which is then

converted to a useable analog input for our vibration suppression components. All sub-

system and circuit power consumptions are listed in Table 3.

3.4 Software Design This section outlines the approach SAVSS implemented for data logging for the four

accelerometers and the piezoelectric damper control. Because the microcontroller unit

needed to complete several simultaneous tasks at speeds that met or exceeded the

aforementioned constraints, a PIC32MX360F512L Microcontroller was selected. The

PIC32, part of the PIC32 Starter Kit as seen in Figure 14, has a maximum speed of 80

Table 3: Total Power Consumption

Figure 14: PIC32


RockSat-C 2011

MHz, which was needed to complete the multitasking demanded of it. The PIC32 Starter

Kit has an internal oscillator, and 16 channels for analog-to-digital conversion. In order

to properly interface with an SD Card, the Port I/O Expansion Board was used. This

section goes into detail how the PIC32 communicated with the SD Card, and the four

accelerometers.

3.4.1 Microcontroller Unit: Accelerometers Analog to Digital ConversionAs

mentioned, four accelerometers where used in order to obtain adequate amount of thrust-

axis vibration and acceleration data the Terrier-Orion Rocket will experience during the

entire length of the flight. A high-G ADXL78 accelerometer provided by Analog was

placed on both the rigid and the damped platforms. Likewise, a low-G ADXL103 was

used on both the rigid and damped platforms. Using the internal PIC32 multiplexer, the

ADC was able to convert the accelerometers‟ analog output to 10-Bit forms at 1 MSPS,

which allowed each accelerometer‟s value to be converted at 250 KSPS. By using the

PIC32‟s Direct Memory Access (DMA) scheme, the data was stored directly into the SD

Card at that same sampling rate. Using the DMA allowed the PIC32 to spend more

operating time handling the damper control routine. At 1 MSPS, and given a maximum

flight time of 1000 seconds, the total amount of memory needed was 10 megabytes.

Because it used a 16 gigabytes memory card, the SAVSS system met this constraint. A

downside to meeting this constraint was that the memory was organized in the SD Card

serially. This meant that storing the clock time of each sample of acceleration data was

not possible, because this would require a memory buffer and time stamp appendage to

each sample. Instead, the timeline of the flight was provided by Wallops Flight Facility.

The software flow diagram can be seen in Figure 15.

Figure 15: Software Flow Diagram


RockSat-C 2011

3.5 Mechanical Design

As one of the subsystems, the mechanical design dealt with more of the stringent

constraints defined by the NASA RockSat program. The payload was integrated into the

top half of the canister shown in Figure 3.2. The other bottom half of the canister was

shared with a team from Drexel University. The biggest challenge faced was designing an

active vibration suppression system utilizing DuraAct Piezoelectric patches with the

maximum mass of 6.5 lbs, maximum height of 4.75 inches and maintaining the center of

gravity of the canister within a 1x1x1 inch envelope of canister.

The hardware system was divided into three subsystems that included the structure,

integration, and mass & center gravity. All the subsystems had to work harmoniously

with each other in order to meet the requirement. A

proper structure had to be designed in order to

make the thin piezoelectric patches suppress the

vibrations of certain damped plates and to fit both

electrical and mechanical components. The total

mass and center gravity constraints and the built

structure had to be considered when integrating

components.

3.5.1 Structure Design

Designing the structure was the primary subsystem

of hardware design. A proper structure enabled the thin Piezoelectric patches to suppress

the damped plates while meeting the height constraint. According to the RockSat-C

user‟s guide, the total usable space of the payload canister was limited to the dimension

of 9.3” in diameter and 9.5” in height. Since the

canister space was being shared with a team from

Drexel University, the usable space was half of the

total space. Ideally, the maximum height was 4.75”

without consideration of height loss after

integrating with Drexel Team‟s payload and the

canister skin.

Shown in Figure 17 is a rigid plate body with four

main standoffs connected between two Makrolon

plates. The bottom of the rigid plate body was

rigidly screwed to the top of Drexel Team‟s

payload and the top of the rigid body was mounted

to the cap of the canister skin.

In Figure 16, the damped plate body shown with 3” usable height. Most of the electrical

components were integrated on the damped plate body. The 3” plate-to-plate height was

chosen because the total height of PIC32 expansion board with the SD Card integrated

stood just below 3 inches. Compared to the rigid plates, the damped plates had four more

big holes on each plate. These four holes were created as the shaft hole for the four main

standoffs of the rigid plate body to freely move through.

Figure 17: Damped Platform

Figure 16: Rigid Platform


RockSat-C 2011

The overall structure assembly is illustrated in

Figure 18. The damped plate body was damped between the two plates of rigid body.

Two Piezoelectric patches were mounted to inner surface of each rigid plate with

cushions beneath them. Rectangular Makrolon plates were used as cushion in order to

adjust the distance between rigid plates and damped plates. Since the bending height of

the patches was 0.5 mm, Makrolon cushions were used to make sure that the patches had

constant contact with the damped plates.

3.5.2 Integration


RockSat-C 2011

After the structure design had been determined, integrating all of the components was the

next crucial subsystem. The overall mechanical design is shown in Figure 18. Since 8

Nica 5A batteries and the DC/DC converter are the major weight units in our design, they

were designed to be placed on two ends of payload in order to balance overall center

gravity. Based on this idea, there was not enough space in the middle of damped plates

for Pic 32 board. Therefore, Pic 32 was mounted upside down on the top of rigid

platform.

As shown in Figure 19, only few of small components were mounted on the bottom plate

of damped body, such as 2 9V batteries and G-switch. One of two accelerometer PCB

boards with low Z and High Z was determined to be mounted upside-down on the bottom

of top rigid plate due to insufficient space on the bottom of damped plate.

Figure 18: Fully Integrated Structure


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The other set of accelerometer

PCB boards were designed to be

mounted on the bottom of the top

rigid plate. Due to narrow space

between the rigid body and the

damped body, rectangular hole

was cut on the top of the damped

plate so that this accelerometer

PCB board could pass through the

rigid plate and not obstruct the

experiment.

As illustrated in the Figure 3.16,

two patches were mounted to the

inner surface of each rigid plate

by 45 degrees. With this crossed arrangement, the damped body would be balanced. Any

slight unbalancing could throw the entire system off when dealing with such

environmental factors such as vibration and high G-forces.

3.5.3 Mass and Center of Gravity

According to NASA‟s requirement, the entire weight of all involved projects on board the

RockSat-C rocket must be 20±0.2 lbs. After subtracting the weight of canister, its skin

and the plate in the middle of canister from the total weight, then taking half, the

maximum allowed weight was 6.5 lbs. As shown in Table 4, the total mass of the

complete systems was currently estimated at 3.6 lbs, which is under the constraint of 6.5

lbs. Once all the masses of each payload were known, “dummy” weights were distributed

about the canister in order to meet the required weight. The locations of the weights in

the vertical axis of each payload must also be known to accurately distribute the weight

throughout the canister.

With the combination of payload‟s weight and height, the center of gravity of the canister

Figure 19: Integrated Electrical Components

Table 4: Mass Budget


RockSat-C 2011

could be known. RockSat-C user guide requires that the center of gravity of the canister

must lie within a 1x1x1 inch envelope of the RockSat payload canister„s geometric

centroid. After carefully measurements of each component, each actual mass was

assigned to each corresponding component in SolidWorks. By running the mass property

feature in SolidWorks, the total mass and center gravity were both calculated. Simulation

of center of gravity had been completed within the Solid Works environment and the

result was shown in Figure 20. By observing the pink XYZ coordinate system, one can

estimate that the center gravity of this half payload was in the middle. As calculated by

SolidWorks, the center gravity for this payload was X 0.28”, Y -0.12”, Z 2.14”. This

center gravity coordinates are based on the origin locates at the center of bottom plane.

Z=2.14” means the Z coordinate is 2.14 inches above the origin, which is within 1 inch

envelope in the Z-axis. Therefore, the center gravity in X and Y-axis had met the NASA

requirement. The origin of the coordinate system was at the center of the bottom of rigid

plate. 2.14” above the origin met expectations and was recalculated after integrating with

the Drexel payload. Dummy weights were added to the payload to reach total weight of

20 lb as well as adjustment of center gravity.

4.0 Student Involvement (0.5 – 1 page)

Figure 20: SolidWorks COG Test on Fully Integrated System


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5.0 Testing Results

Mechanical: The mechanical systems were tested mostly utilizing SolidWorks.

Center of Mass and Center of Gravity tests were run so as to know whether or not

the entire system would comply with all NASA regulations.

Electrical: Each electrical subsystem was tested 1st individually and then all

together. We first tested each of our power supplies. We needed 2 9V batteries to

power the Pic32 microcontroller and 8 NiCa 5A batteries to power the

piezoelectric transducers. Each power supply needed to last for 6 minutes since

our project was only concerned with the first 6 minutes of the flight. We powered

on the system and verified that each of the supplies would in fact stay on for a full

10 minutes, leaving room for error.

We then tested the high voltage DC/DC converter which was needed to control

the piezoelectric transducers. We sent 9V signals into the component and

measured 300V as the output.

Software: We powered up the entire system and let it run for 10 minutes,

checking for data storage functionality. The Pic32 saved accelerometer data from

4 separate accelerometers: 2 gaining readings from the rigidly attached platforms

and the other 2 from the damped platform.


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6.0 Mission Results

Unfortunately, our payload did not return any meaningful results. The aim was to

eject the SD card from the Pic32 post-flight and analyze the accelerometer data

from both the rigid and floating plates. However, this was not completed. The SD

card had only two files saved to it from the Pic32 which had actual data in them,

both of which containing only non-sense. There were several other files saved to

the SD card, however they would not open up because of a read-write failure. It is

extremely possibly that our damping system did in fact function the way it was

designed for; however, without being able to access these files we will never

know.

This comes as a great disappointment to us, for a year of mechanical and

hardware design has gone unproven because of software problems. We can only

hope that if this project is continued next year, that actual results of accelerometer

data are retrieved from the payload so as to analyze the functionality of the

dampening system.

7.0 Conclusions

In conclusion, our design didn‟t successfully achieve expected goals since there

was no data stored on the SD card. The reasons of this cause are not yet decided.

However, it may be due to the following reasons.

1. Pic32 Microprocessor itself: according to many other Pic32 microprocessor

users, it‟s not a very user-friendlier microprocessor. It frequently goes wrong

and output wrong data. Sometimes the SD cards were burned for no reason.

2. Short circuit: Pic32 didn‟t work when we first arrived in Wallops. Later on we

found out two pins of the Pic32 daughter board were pressed, which led to

short circuit. After separating these two pins, Pic32 could store data

successfully.

3. Soldering: Pic32 could still successfully store data the night before we

soldered all the wires on the pic32. After soldering, it didn‟t work well.

8.0 Potential Follow-on Work

The SAVSS could be added to and worked upon by a future team in order to gain

better, more concrete results. It seems plausible that if the same piezoelectric

patches were used as dampers, but attached differently so as to suspend the

floating platform with more “cushion,” that a greater damping ration could be

attained. Also, a different microcontroller would absolutely have to be used. The

Pic32 gave many problems throughout the year and then again during launch.

Although the true problem still is not 100% known of why no data was saved on

the SD card, a possibility is because of the Pic32 and its incompatibility.

The actual control of the damping patches could be improved on as well. In this

design, the SAVSS eventually had to either apply 0V or 300V to the patched,

meaning an all-or-none displacement of the patches in the z-axis. If an analog

amplification circuit was designed, using power MOSFETS, the patches could

potentially be delivered an all-inclusive variable voltage from 0V to 300V. This


RockSat-C 2011

would make the movements of the patches, and therefore of the floating platform,

much more precise and less jerky, leading to a better floating-to-rigid damping

ratio.

9.0 Benefits to the Scientific Community

If our design had worked as we expected it to (which it may have, however we

have no proof because of the foul up by the Pic32/SD card) then the scientific

community could benefit in one major way. The product, if worked on and

expanded into a larger but similar design, could allow for fragile components to

be flown on sounding rockets which would otherwise not be able to handle the

vibrations experience throughout a typical flight. This safe and steady platform

could lead to new scientific research which needs fragile components in order to

gain data.

10.0 Lessons Learned

While it is hard to deem this mission a success because of there is no data to show

for the sub-orbit experiment, this mission was a success if we look at the lessons

that we have learned from this experience. We knew the PIC32 had problems for

months ahead of time. If we had gone in a different direction for the data

retrieval, we could know more about whether the experiment actually

worked. We should have selected a user-friendlier microprocessor such as the

Adruino. Had we used a simpler board, we could have spent the time on the

piezoelectric dampers that were the focus of our experiment.

In order to focus and ensure that the piezoelectric dampers would have worked

properly, we really should have spent more time implementing the linear voltage-

to-stiffness amplifier that we could not implement due to timing constraints. With

an amplifier like this, we could have adjusted the stiffness of the dampers to

counter the mechanical vibrations that the rocket underwent. Our backup plan,

which we actually used, simply pulsed the dampers when the vibrations exceeded

a certain threshold.

We really would have preferred testing the software and hardware more

thoroughly, but that was impossible due to many factors but mostly due to our

design schedule. We would have liked to create a LabVIEW graphical user

interfaces to thoroughly test the hardware and software under every scenario

possible. This also would have allowed us to test this actively while the entire

experiment was on a vibration table.

There were a lot of things we did not have the time to accomplish. This is our

fault. We should not have selected such a difficult subject matter such as

piezoelectric dampers. We should have selected something simpler that required

less sophisticated technology than that that we did select. To adequately utilize

these piezoelectric dampers, an analog feedback circuit is typically required.


RockSat-C 2011

Documents

RockSat 2010 Final Report Template