Development of DARPA Grand Challenge Vehicle

Non-These Project Report

Presented in partial fulfillment of the requirements for

The Degree Master of Science in the

Graduate school of The Ohio State University

By

Mark Soda

* * * * *

The Ohio State University

Winter 2005

Master’s Examination Committee: Approved by Dr. Umit Ozguner, Advisor ________________

Advisor Dr. Steven Bibyk Department of Electrical

Engineering

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Table of Contents

Brief Overview of The Grand Challenge............................................................................ 3 1. Summary of 2004 Challenge ...................................................................................... 3

1.1. Lessons learned................................................................................................... 3 2. Challenge 2005 ........................................................................................................... 4

2.1. Vehicle Platform ................................................................................................. 4 2.2. Actuators ............................................................................................................. 5

2.2.1. Steering ....................................................................................................... 5 2.2.2. Throttle........................................................................................................ 7 2.2.3. Brake ........................................................................................................... 8 2.2.4. Gear Shift .................................................................................................... 9

2.3. Sensors .............................................................................................................. 10 2.3.1. LIDAR ...................................................................................................... 11 2.3.2. Doppler Radar........................................................................................... 14 2.3.3. Rotating RADAR...................................................................................... 15 2.3.4. Brake Pressure .......................................................................................... 16 2.3.5. GPS ........................................................................................................... 17 2.3.6. Wheel Speed ............................................................................................. 18 2.3.7. Ultrasonic.................................................................................................. 20

2.4. Miscellaneous ................................................................................................... 21 2.4.1. Additional Fuel Tank ................................................................................ 21 2.4.2. Trailer for the Ranger................................................................................ 21 2.4.3. Bumper extension ..................................................................................... 23 2.4.3.1. Other ..................................................................................................... 25

3. Summary/Conclusions .............................................................................................. 27 Appendix A: Actuator Datasheet Web Addresses ............................................................ 29 Appendix B: Sensor Datasheet Web Addresses ............................................................... 29

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List of Figures

Figure 1: Steering Servomotor Sketches............................................................................. 6 Figure 2: Steering Coupler (left) and Motor Installed (right) ............................................. 6 Figure 3: Steering Motor Mount ......................................................................................... 7 Figure 4: Throttle Mount and Link Sketch ......................................................................... 8 Figure 5: Throttle Actuator ................................................................................................. 8 Figure 6: Brake Actuator Connection Sketch ..................................................................... 9 Figure 7: Gear Shift ............................................................................................................ 9 Figure 8: Gear Shift Actuator ........................................................................................... 10 Figure 9: Proposed Sensor Placement............................................................................... 11 Figure 10: SICK LIDAR................................................................................................... 11 Figure 11: Back of LIDAR and Pin Connector ................................................................ 12 Figure 12: Top View LIDAR Coverage ........................................................................... 12 Figure 13: Front View LIDAR Coverage ......................................................................... 13 Figure 14: Lower LIDAR Mount Sketch.......................................................................... 13 Figure 15: Front LIDAR Mount ....................................................................................... 14 Figure 16: Upper LIDAR Mount (LIDAR not Present) ................................................... 14 Figure 17: Front Radar Mount .......................................................................................... 15 Figure 18: RADAR Mount Sketch ................................................................................... 15 Figure 19: Rotating Radar Dish ........................................................................................ 16 Figure 20: Brake Sensor.................................................................................................... 17 Figure 21: GPS Antenna Mount ....................................................................................... 18 Figure 22: Front Brake Rotor............................................................................................ 19 Figure 23: Front Wheel Speed Calculation....................................................................... 19 Figure 24: Wheel Speed Sensors ...................................................................................... 20 Figure 25: Ultrasonic Placement and Coverage................................................................ 20 Figure 26: Ultrasonic Sensor (MASSA M5000/95) ......................................................... 21 Figure 27: Ohio Trailer Supply Business Card................................................................. 22 Figure 28: Trailer Quote ................................................................................................... 23 Figure 29: Tubular Techniques Business Card................................................................. 24 Figure 30: Bumper Extension Sketch ............................................................................... 25 Figure 31: Bumper Extension ........................................................................................... 25 Figure 32: Computer Cabinet............................................................................................ 26

List of Tables Table 1: Ranger Specifications ........................................................................................... 4 Table 2: Steering Actuator Connection Analysis................................................................ 5 Table 3: Ranger Vs. Trailer Dimensions .......................................................................... 21 Table 4: Ranger Height Reduction Options (Need 9”) ..................................................... 22 Table 5: Bumper Extension Mounting Analysis............................................................... 24

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Brief Overview of The Grand Challenge The Grand Challenge is a contest hosted by the Defense Advanced Research Projects

Agency (DARPA) to build a vehicle that can autonomously navigate its way long distance in unknown off-road conditions. Two hours before race time, the teams are given GPS points of the ‘route’ to be followed, and must remain within certain boundaries. Since the GPS points can be spaced far apart, as well as many natural and intentional obstacles on the route, the vehicle must have adequate sensing capabilities and obstacle avoidance algorithms. To win the competition, a team’s vehicle must successfully complete the course in the least amount of time, and be under the 10-hour time limit. In the 2004 race out in Las Vegas, no team completed the course and so the 1 million dollar prize went unclaimed. This year, for the October 8, 2005 in the desert southwest, the prize has been doubled to 2 million!

1. Summary of 2004 Challenge For the 2004 Grand Challenge, The Ohio State University partnered with Oshkosh to

form team Terramax. The race vehicle was an Oshkosh MTVR, which is very large 6x6, 32,000 lb, diesel military truck. My contribution to the project was to outfit the MTVR with the required sensors, computers, and supporting hardware to make it autonomous. With help from two Oshkosh fabricators, we were able to finish the hardware portion of the project on time.

Team Terramax successfully passed qualifications and was one of 15 teams to

compete for the 1 million dollar prize. No team finished the race, with the farthest vehicle traveling 7 miles before getting stuck. Terramax went about 2 miles before a known problem with the network ceased communications between the computers and ended the race for us.

1.1. Lessons learned It was evident in the qualifications and the race that all teams suffered from lack of

time. Like us, most teams had all the hardware in place (sensors, actuators, computers, etc.), but the software was lacking. The sensors are the eyes and ears of the computer and the actuators are its muscles, but without the right software, the computer cannot control these muscles correctly.

The software is much more complex and difficult to develop than the hardware. The

vast amounts of data and processing power required to interpret all the senor data requires multiple computers, making inter-computer communications an issue. Also, complex code is required to analyze the data and make control decisions. The lack of time to debug the system and the code was the main reason for all the team’s failures.

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2. Challenge 2005 For the 2005 challenge, Oshkosh will not be partnered with OSU, we will be working

on our own. Our new race vehicle is a much smaller and more maneuverable Polaris 6x6 Ranger. All the equipment was stripped from the Terramax and is available for use on the Ranger. Each and every one of the tasks required to make the Terramax autonomous has to be repeated on the Ranger. This is my task once more and the focus of this paper.

2.1. Vehicle Platform The 2005 Challenge vehicle is a Polaris 6x6 Ranger. It has a 500cc 4-stroke engine,

Polaris variable transmission (PVT), and a top speed of 41 mph. Table 1 lists the basic specifications, a complete list can be found at:

http://www.polarispowersports.com/ranger/6x6.shtml

Table 1: Ranger Specifications

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2.2. Actuators Full computer control of the Ranger requires four actuators to manipulate the

steering, throttle, brake and gear lever. The next four subsections provide descriptions of the actuators and how they are mounted.

2.2.1. Steering For the computer to steer the Ranger, a servomotor must be connected to the

steering mechanism. A SmartMotor™, RTC 3000 controller, and planetary gearbox from Animatics were purchased for this purpose (Appendix A). The servomotor can be connected in parallel with the steering wheel or it can replace the steering wheel for a true drive-by-wire system. Table 2 highlights the pros and cons of each connection method. Due to space constraints and for simplicity, the Ranger will be steer-by-wire only. The existing steering wheel will be completely removed and the servomotor directly connected to the steering box.

Table 2: Steering Actuator Connection Analysis

Advantages Disadvantages Parallel the Servomotor with the steering wheel

• Maintains the mechanical steering link for easy manual driving and safety

• Complicated to implement • Requires additional space • Additional load on

Servomotor • Need a clutch to disengage

servomotor in manual mode• Potentially less reliable

Servomotor only (Steer-by-wire)

• Simple direct mechanical connection to steering box

• Requires least amount of space

• Better actuator reliability over parallel system

• No mechanical link for manual steering.

The Ranger has a basic rack and pinion steering system that is connected to the

steering wheel through a shaft with two u-joints and spline connectors. A mount for the motor and a shaft to couple the motor to steering box had to be fabricated. Fortunately there was enough room above the steering box that the servomotor could be mounted directly above it. This is very desirable because it allowed the mount to be mounted so that the shaft of the servomotor and the spline input of the steering box line up, directly opposing each other. This eliminates any possibility of binding and makes the coupling shaft much easier to fabricate. The existing steering shaft (P/N 53824B) was modified to build the new coupling shaft. The shaft was cut down to 1½” at the end connected to the steering box, keeping spline connector and its U-joint. A heavy-duty spider coupler was purchased to connect the modified shaft with the servomotor, as well as to provide shock protection for the motor (Figure 1A and Figure 2 left). The spider coupler connects to each shaft with a

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half-moon keyway and a setscrew. A grove was milled into the steering shaft for the keyway. The motor came already keyed and no modification was needed.

A. Servomotor Coupler Sketch B. Servomotor Mount Sketch

Figure 1: Steering Servomotor Sketches

Figure 2: Steering Coupler (left) and Motor Installed (right)

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The steering rack was removed from the Ranger to facilitate making the motor mount. The mount was made from aluminum C-channel stock, which is very rigid and resistant to twisting and flexing (Figure 1B and Figure 3). The motor bolts to the mount using a bracket that it came with. The mount is bolted to the Ranger using the same 3 bolts that hold the steering box to its frame (Figure 1B and Figure 2, right picture, at the bottom). These bolts were grade 5 and ½”too short with the addition of the motor mount. They were replaced with much stronger, grade 8.8+ bolts of the required length.

The motor, mount and coupling shaft worked perfectly in testing. The motor can turn the wheels all the way from one side to the other in about 2.5 seconds, with no visible twisting or flex in the mount. The coupling shaft rotates smoothly and without binding.

Figure 3: Steering Motor Mount

2.2.2. Throttle As with most cars, the gas pedal of the Ranger is connected to a cable, which

moves a mechanical throttle valve on the engine that controls the speed of the engine. For the computer to be in command of the engine speed, an actuator is needed to manipulate the throttle valve. As with the steering motor, the actuator can be connected in parallel or it can replace the gas pedal for a true drive-by-wire system. The latter was chosen using similar reasoning to the steering decision.

A 722 Series linear actuator by ADDCO was selected for throttle control. The

722 is a four point acme screw, all gear drive, with 30lbs push or pull force, travel up to 3in per second and a built-in position feedback potentiometer. A website with complete specifications is listed in Appendix A.

The 722 actuator was mounted underneath the dashboard to a frame member

using pipe clamps. The cable that controls throttle valve was removed from the gas pedal, redirected and connected to the linear actuator using a fabricated link plate (Figure 4). The actuator has more distance of travel than the throttle valve, so to prevent damage from over excursion the cable was connected so when the actuator is fully retraced the throttle valve is fully open. When the actuator is fully extended, the throttle valve is closed and there is extra slack in the throttle cable, which has no adverse affects. Figure 5 is a picture of the actuator installed.

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Figure 4: Throttle Mount and Link Sketch

Figure 5: Throttle Actuator

2.2.3. Brake The hydraulic braking system of the Ranger is identical to that of a car; expect

there is no power assist. The brake pedal is connected to the master cylinder and a force on the pedal causes the master cylinder to produce a pressure on the hydraulic fluid. The hydraulic fluid travels down the brake lines to the brake calipers, which are mounted on the hubs of the four-corner tires. The hydraulic pressure will cause the calipers to squeeze the brake pads against the rotors, reducing vehicle speed.

For the computer to control the braking system, it must be able to exert and

regulate a force on the braking system. A linear actuator with significant pulling force is most suited for this purpose. The actuator could replace the brake pedal and be

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connected directly to the master cylinder (brake-by-wire). However, this is not safe since a computer malfunction could prevent the driver’s ability to apply the brakes. To avoid this problem, the actuator will be connected in parallel with the brake pedal using a braided steel cable. Thus in the case of a failure, the driver can still manually apply the brakes, even if the actuator is stuck fully extended (Figure 6). At the time of this writing, no actuator had been purchased and this is an incomplete task.

Figure 6: Brake Actuator Connection Sketch

2.2.4. Gear Shift A hand lever next to the steering column controls gear the vehicle is in (Figure 7).

The lever is connected to a cable that moves another lever on the side of the transmission, which changes the gears. A linear actuator made by Ultra Motion (P/N D-A083-HT17-4-P-RBC4/EC4, Appendix A) allows the computer to operate the gear shifter (Figure 8). The actuator will be mounted near the transmission and in such a way that the vehicle can be manually switched into neutral incase of a failure, as required by the Challenge rules.

Figure 7: Gear Shift

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Figure 8: Gear Shift Actuator

The actuator is a ball-and-screw design driven by a stepper motor. A stepper motor controller connects to the actuator and commands its motion. The controller receives a desired position and a modulated frequency that sets the speed of the actuator’s movement. A suitable mounting method has yet to be determined and this is an incomplete task.

2.3. Sensors Sensors give ‘eyes, ears and a sense of touch’ to the computer. At the present time,

no one sensor that can completely make the computer aware of its surroundings, so a number of different sensors must be used. Each sensor is designed to be particularly good at detecting some object or event. For example, a LIDAR is good at detecting medium to large objects that reflect some amount of light. It is not particularly good at detecting small and thin things like a barbwire or chain link fence. RADAR on the other hand can detect these objects fairly well.

The vehicle will hopefully be traveling forward almost the entire time, so a majority

of our sensing power will be directed forward. At the time of this writing, the proposed sensor placement (Figure 9) for the front of the Ranger includes: two LIDARs at different heights scanning horizontally, a low mounted Doppler RADAR, a high mounted rotating RADAR, stereo vision cameras and an ultrasonic sensor on each corner of the bumper. The sides of the Ranger will only have ultrasonic sensors to detect the distances from near by objects such as tunnel walls. No rear facing sensors have been proposed yet. A GPS antenna on top of the Ranger and an inertial measurement sensor will be used to determine spatial position and heading.

Along with the sensors to detect the environment, there are additional sensors on the

ranger to sense actuator functionality and vehicle parameters such as engine RPM and wheel speed. The following subsections give descriptions of the various sensors that the Ranger will be equipped with and how and why they were mounted where they are.

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Figure 9: Proposed Sensor Placement

2.3.1. LIDAR A LIDAR (Light detection and ranging) sensor detects the distance and position

of objects in a 180° scanning field using a LASER beam. The LIDARs are by SICK, part number LMS221-30206 (Appendix B) and can detected objects up to 80m away, and with 0.5º resolution (Figure 10). They require 24Vdc and consume 37 watts max. The power is supplied by a 24Vdc, 6.5A supply mounted in the computer cabinet. This supply can power up to 4 LIDAR sensors. The LIDARs communicate to a computer using RS-232 for 10-meter or less cable distances and RS-422 for up to 1200-meters. The pin-out diagram for the electrical connector is shown in Figure 11.

Figure 10: SICK LIDAR

Front of Ranger

Back of Ranger

Front Sensors: (2) LIDARs Doppler Radar Rotating Radar (2) Ultrasonic Stereovision cameras

Passenger Side Sensors: (2) Ultrasonic

Driver Side Sensors: (2) Ultrasonic

Rear Sensors:None yet

Internal: INS GPS

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Figure 11: Back of LIDAR and Pin Connector

The LIDAR sensor is large and heavy, so its mount must be rigid and sturdy as well as the mounting point to the vehicle. At this moment, the senor plan calls for two LIDARs, but this number is not definite. One LIDAR sensor is mounted so it is scanning horizontally on the front brush guard of the Ranger. This will give a view of all objects in the plane of space in front of the vehicle two feet high of the ground (Figure 12). Objects tall enough to be detected by this LIDAR are to be avoided since they cannot pass underneath the Ranger. The second LIDAR is also mounted horizontally, but higher up on the wood crossbar at a height of four feet. This arrangement will help to ascertain the height of an obstacle. It also assists detecting objects that might not be seen well by the lower LIDAR such as a tree or tall vehicle, which are narrower close to the ground (Figure 13).

Figure 12: Top View LIDAR Coverage

LIDAR Coverage

Front

Back

RANGER

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Figure 13: Front View LIDAR Coverage

The LIDAR comes with its own mounting bracket that has one degree of tilt adjustment and a rotational adjustment. A mounting plate was built to go between this bracket and the Ranger’s bumper because the bars of the bumper are spaced too far apart to use the bracket as is, and also the bars are tilted, the top bar is 1” back from the bottom bar (Figure 14). The mount was made out of 6”, ¼” thick aluminum plate. The LIDAR bracket bolts to the mount and the mount bolts to the bumper using carriage bolts and 1” pipe spacers on the top bolts to make it level (Figure 15).

Figure 14: Lower LIDAR Mount Sketch

Lower LIDAR

Upper LIDAR

Front of Ranger2’

2’

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Figure 15: Front LIDAR Mount

The second LIDAR is mounted to the lower horizontal wooden bar that is bolted to the roll cage. In this case the LIDAR bracket could be used as is (Figure 16).

Figure 16: Upper LIDAR Mount (LIDAR not Present)

2.3.2. Doppler Radar The Doppler RADAR (Radio detection and ranging) sensor is an EVT-300 by

Eaton Vorad (Appendix B). It was developed as part of a collision avoidance warning system for tractor-trailer trucks. This sensor operates using the Doppler effect and only detects metal objects in relative motion to the sensor. The output is a detected object’s distance and relative speed. The RADAR requires 12 to 24 VDC and consumes 20 watts. It operates at 24.725 GHz with a 12°-beam width.

Like the lower LIDAR, the RADAR is mounted low down on the front brush

guard to detect objects that the Ranger cannot safely drive over (Figure 17). The mounts are made out of strips of aluminum and bolted to the brush guard with long carriage bolts. Instead of using tube spacers, a nut was used on each side of the mount. This provides tilt and left/right adjustment of the sensor (Figure 18).

Brush guard

Mount (built)

Bracket (Supplied with LIDAR)

Back of LIDAR

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Figure 17: Front Radar Mount

Figure 18: RADAR Mount Sketch

2.3.3. Rotating RADAR A team of students led by Dr. Lee is developing a rotating radar dish to help us

detect objects. The RADAR reflector is a digital TV satellite dish by DirectTV™ (Figure 19). The students are developing the transmitting/receiving horn electronics and signal processor. Our team is responsible for building the mount to hold the dish and rotate it back and forth. The exact range of rotation has not been determined yet but will be equal to or less than 180°. The mount and drive motor will need to be very sturdy. The wind resistance of the dish and the bouncing of the vehicle will generate large forces that need to be tolerated. The exact placement of the dish has not yet been decided, but the present idea is on the lower wooden bar next to the LIDAR on the passenger side. The ideal place would be on the top of the Ranger, but there it would block and interfere with

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GPS reception. Accurate GPS information is more critical and obstacle data is available from other sensors. The dish mount still needs to be designed and a drive motor selected.

Figure 19: Rotating Radar Dish

2.3.4. Brake Pressure A brake sensor is required to give feedback to the computer concerning how

much force the brake actuator is exerting to the break pedal and thus the amount of braking being applied. Since the Ranger has hydraulic brakes, a pressure sensor connected to the hydraulic line from the master cylinder will give the desired information. The MSP600 series pressure transducer by Measurement Specialties (P/N MSP6252P3-1, Appendix B) with a 0 - 2500 psi range was purchased from www.digikey.com at a cost of $96.25.

The sensor requires a 5V supply and less than 10mA of current. The output is

a linear analog signal from 0.5 (0 PSI) to 4.5V (2500PSI). To calculate the output pressure the following equation can be used:

Pressure (PSI) = Max PSI*(Vout-Vmin)/(Vmax-Vmin) = 2500PSI*(Vout-0.5V)/4V The existing brake system had a distribution block that split the main

hydraulic line from the master cylinder to the front brakes and also to a pressure

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switch for the taillights. To connect the sensor, a tee was inserted where the pressure switch connected to the distribution block. The sensor has a standard 1/4 NPT pipe thread and the appropriate coupler was purchased to connect to the tee. In Figure 20 the added brake pressure senor is the big silver tube inline with the tee and the brake switch for the taillights protrudes out to the right.

Figure 20: Brake Sensor

Testing of the break pressure sensor revealed that we could generate a maximum

hydraulic pressure of 1930psi, by stepping on the break pedal as hard as we could. For our application the sensor has an adequate range and should provide enough resolution.

2.3.5. GPS GPS is critical for determining spatial locality in reference to the desired path of

travel that is conveyed from DARPA as a list of GPS points. For the best GPS signal reception, the GPS antenna should be mounted as high as possible with no obstructions. Novatel makes the antenna that we are using; model GPS-600 LB (Appendix B).

On the Ranger, a 2x6” board was placed and centered across the top of the roll

cage using two large u-bolts to secure it. The board over hangs the back of the roll cage by six inches and at the end of this over hang is a 5/8” threaded bolt sticking up to which the GPS antenna screws onto (Figure 21).

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This location makes the antenna the highest point on the vehicle and clear of obstructions. It also offers a very mechanically secure mounting point and convenient location for routing cabling. There is no concern for it being outside of the roll cage because its height is much less than the maximum allowed height as dictated by the challenge rules. In the very unlikely case of a roll over, the GPS antenna is of minimal concern in comparison to the rest of the equipment.

Figure 21: GPS Antenna Mount

2.3.6. Wheel Speed The wheel speed sensors will be mounted on each of the four corner tires.

Magnetic sensors normally used to count the teeth on a gear can be used to detect the holes in the brake rotors (Figure 22). The holes in the center row are equally spaced at 2.22cm and there are 24 holes. The radial distance from the center of the hub to the holes is 8.5cm and to the outer edge of the tire is 30.5cm. It can be calculated from a simple ratio that when the rotor rotates by one set of holes, the tire travels ~8cm (Figure 23). From this, the speed of the tire can be determined.

Speed = (# of holes counted)*8cm / Time

The Magnetic sensors (Figure 24) were purchased from www.digikey.com

($30.24 each) and are produced by Cherry Corp (P/N GS100701, Appendix B). They have a magnet inside and detect the presence of metal by the change in reluctance. They require 4.5-24Vdc and the output is open collector, so a pull-up resistor is required. A test showed that the sensors must be placed within ¼” of the rotor surface for reliable detection. Four simple Z-shaped brackets that connect to the upper brake caliber bolts, and that have a hole for the sensor to mount were fabricated.

GPS Antenna

Top of Ranger Roll Cage

GPS Mounting

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Figure 22: Front Brake Rotor

Figure 23: Front Wheel Speed Calculation

Detect Center Row of Holes

2.22cm

8.5cm

30.5cm

8.5cm

2.22cm

8cm

Rotor

Tire

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Figure 24: Wheel Speed Sensors

2.3.7. Ultrasonic Measurements from ultrasonic sensors are critical when navigating through a

tunnel or tight space. They will be placed on the sides and front of the Ranger for low speed proximity measurements (Figure 25). Two sensors will be placed on each side of the Ranger pointing orthogonal and horizontally outward. The two front sensors will be angled 45° from orthogonal to help detect the entrance to a tunnel.

The ultrasonic sensors are made by Massa (P/N M5000/95, Appendix B) and

require 12-28VDC, 80mA max (Figure 26). They are addressable and can be configured in a daisy chain configuration. Communication protocol is RS485. The sensor transmits a narrow conical 8° beam of sound pulses of 95kHz at a user-selected rate and can measure targets at a range of 0.3m to 4.0m. Their exact placement has not been determined and so they are not mounted yet.

Figure 25: Ultrasonic Placement and Coverage

Front of Ranger

Back of Ranger

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Figure 26: Ultrasonic Sensor (MASSA M5000/95)

2.4. Miscellaneous

2.4.1. Additional Fuel Tank The Ranger came with an eight-gallon fuel tank that will be replaced with one of

a larger capacity. We need to find or figure out the fuel consumption requirements of the Ranger and calculate how much fuel we will require to complete the 175-mile course as well as reserve fuel. A recommendation would be to purchase a fuel cell tank that automotive racecars use. These tanks are made out of 20 gauge steel and have a foam block inside that reduces both fuel sloshing and fuel leakage incase of a tank puncture. They are certified by racing associations and should be acceptable to DARPA. The cost is around $250 for a 25-gallon tank.

2.4.2. Trailer for the Ranger A trailer for the Ranger is required for transporting it out to Las Vegas, as well as

for storing it at night and in bad weather. We currently have a 6’x14’ trailer that is wide and long enough to hold the Ranger, but is not tall enough (Table 3).

Table 3: Ranger Vs. Trailer Dimensions Trailer Ranger Clearance

Width 62" 60" 2" Height 66" 75" -9"

The options to use the existing trailer include: reducing the height of the Ranger, increasing the height of the trailer, or some combination of the two. Modification to the height of the trailer would be very difficult and would reduce the structural strength and thus is not a viable option. A few solutions are presented in Table 4 to reduce the height of the Ranger.

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Table 4: Ranger Height Reduction Options (Need 9”) Method H Advantages Disadvantages Deflate the tires 1.5” - Takes time

- Need to Re-inflate Suspension has 6.25” of travel. Compress springs with spring compressors

~5” - Need to do for each tire - Potential danger

Shorten the roll cage 10” - Easy drive in/out of trailer

- Requires moderate modifications to roll cage - Occupant will hit their head on the back of the roll cage - Occupant’s head will stick out the top of the roll cage

Remove the tires 8” - Will not have to cut the roll cage

- Time to remove tires - Time to put tires back on - Put removable casters on it to move around easily - Would need minor spring compression

The frequency with which we will trailer the Ranger, directly dictates the options we choose. If it is rarely done, then removing the tires and using casters is optimal. It will require no modifications to the roll cage, and has no disadvantages except the time to remove and reinstall the tires.

If the Ranger is to be loaded in and out of the trailer often, the only viable option is to shorten the roll cage. Padding will need to be added to the roll cage so the occupant does not bang their head. Also, they will need to be careful while driving the vehicle because their head will stick out the top of the cage. My recommendation would be not to modify the roll cage.

Since all of the above ideas are undesirable, we cannot use our existing trailer, and will need to buy one with a taller door opening (greater than 75”). Ohio Trailer Supply (Figure 27) gave a $1995 trade-in quote for our trailer. A new trailer with all the accessories on the old one plus the larger rear opening (78”), tandem axels and electric brakes would cost $4650, $2655 with the trade-in (Figure 28).

Figure 27: Ohio Trailer Supply Business Card

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Figure 28: Trailer Quote

It was agreed by the team to trade-in the old trailer and buy the new one. A

purchase order has been sent and we are currently waiting to pick it up.

2.4.3. Bumper extension A LIDAR and a RADAR sensor are mounted on the front brush guard of the

Ranger, protruding outward and making them most forward part of the vehicle. If the front of the Ranger comes into contact with an object, without protection, the sensors will be damaged, if not destroyed. To protect them a bolt-on bumper extension that wraps around the sensors was built, and will transfer any impact force around the sensors and to the Ranger’s brush guard.

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The existing brush guard is made out of 1¾”, 0.070” wall steel tubing. For the bumper extension the same diameter tubing was used with 0.090” wall. This was done because the thicker tubing is not only stronger, but also easier to bend and to weld together. The tubing was bent by and purchased from Tubular Techniques (Figure 29) at a cost of $71.48. A sketch and the dimensions of the bumper are given in Figure 30. A 1¾” hole saw was used to fish-mouth the ends of the pipes so they would fit together orthogonal to each other and a tig-welder to weld the vertical and horizontal sections.

The bumper extension can be either welded or bolted to the Ranger’s brush guard. Table 5 highlights the pros and cons of each method. For welding, as a safety precaution for the electrical equipment connected to the Ranger’s frame, every connecter to solid-state electronics would need to be disconnected. In tig-welding, the welder’s ground line gets connected to the vehicle’s frame and the welding currents are in excess of 150A and very noisy. This could potentially cause over voltage conditions to develop on solid-state device input pins if not disconnected, damaging them. The advantage of being removable and not having to disconnect all electrical equipment led to the decision of using bolts.

Table 5: Bumper Extension Mounting Analysis Advantages Disadvantages Weld • No mounting hardware

• Cleaner, more unified look • Permanente, non-removable • Heat could reduce the strength of the

brush guard • Needed to disconnect all vehicle

electrical equipment. Bolt-on • Removable

• Faster to implement • More mounting hardware

To bolt the extension on, vertical holes were drilled in each of the four legs of the

extension near where they meet with the brush guard. 3/8” eyebolts went inside each of the extension tubes with the treaded studs pointing out the ends. Then a vertical bolt went in each vertical hole and through the eyes of the eyebolts. The studs sticking out of the ends line up with holes drilled in the brush guard and bolt on the backside (Figure 30). Using eye-blots gave flexibility to allow for small misalignments in bolting. The finished bumper extension is shown in Figure 31.

Figure 29: Tubular Techniques Business Card

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Figure 30: Bumper Extension Sketch

Figure 31: Bumper Extension

2.4.3.1. Other Other miscellaneous tasks that were completed are listed below: • Mounted LIDAR, steering motor and ultrasonic power supplies inside the

computer cabinet. They were mounted with tie-wraps and double sided tape. The tie-wraps go to tie wrap mounts that are bolted to the side of cabinet (Figure 32).

• Built a folding armrest board for placing the joystick while driving manually. The

board can be removed by pulling out the hinge pin.

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• Fabricated a mount that bolts both a LCD monitor on the inner side of the lower

wood bar and a LIDAR on the outside of the wood bar (Figure 16).

• Started mounting the computers in computer box (Figure 32).

Figure 32: Computer Cabinet

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3. Summary/Conclusions

The experiences and lessons learned from building the Terramax last year facilitated the autonomous modifications to the Ranger. Unlike last year, we have most of the hardware available early on, enabling us to complete the autonomous conversion quickly, giving the software people significantly more time to test and debug their code. Only new actuators were required for the Ranger. With new mounting hardware, Terramax’s sensors and computers can be reused, saving considerable money and time.

Work on the Ranger began at the beginning of this quarter and substantial progress

has been accomplished. Throttle and steer-by-wire are in place, tested and working. Brake and gear shifting-by-wire are soon to come. The basic sensors are mounted and future sensor locations identified. Still, a non-trivial quantity of the hardware remains to be completed.

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APPENDIX

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Appendix A: Actuator Datasheet Web Addresses

• Steering Servomotor (Animatics SmartMotor w/ RTC3000 controller) http://www.animatics.com/web/products.html

• Throttle Linear Actuator (ADDCO 722 Series) http://www.addcoinc.com/specs_i/722_specs.htm

• Brake Actuator Not yet been determined

• Gear Shift Actuator (Ultra motion D-A083-HT17-4-P-RBC4/EC4) http://www.ultramotion.com/products/digit.php

Appendix B: Sensor Datasheet Web Addresses

• LIDAR (LMS221-30206) http://www.sickusa.com/live/master/datasheet.asp?PN=1018022&FAM=Measurement#

• Doppler RADAR (EVT-300) http://www.eaton.com/VORAD/

• Brake Pressure Transducer (MSP 600) http://www.msiusa.com/msp600.htm

• GPS Antenna (GPS-600) http://www.novatel.com/Products/gps600.html

• Ultrasonic (MASSA M5000/95) http://www.massa.com/datasheets/m500095.html

• Wheel Speed Sensor (GS100701) http://www.cherrycorp.com/english/sensors/gs1005_1009.htm