Critical Design ReviewGroup A3: HMS “Bloodhound”

Matt MorrisMatt PrygoskiJay Slaggert

Fred ThwaitesDan Zibton

Tuesday, April 22, 2008Thursday, April 24, 2008

Project Overview• Autonomous Hazardous Material Seek-and-Identify

Vehicle• Use GPS to locate general area of potentially

hazardous material• Use infrared sensor to detect if material is hazardous• Return to starting position when detection is complete

• Independently Driven Rear Wheels– Two 24V Gear Motors

• Front Wheel Casters

• HDPE body

• PVC Boom with Infrared Sensors

• GPS Navigation System

Key Features

Abstract• Purpose: to design a hazardous material seek and identify vehicle that is capable of autonomously locating, sampling, and identifying a target that could possibly be hazardous material

•Important Goal: Simple and Durable

• Target customers:• Military• Law enforcement agencies• HazMat clean-up crews

Design Requirements• Powered by at most 20V battery• Move to a location within +/- 1m specified

by provided coordinates• Travel on grass, dirt, concrete, and asphalt• Body no larger than 2m in any direction• Complete search in under 5 minutes

• Accurate– Capable of moving to with in +/- 1 m of a target.

• Robust– Capable of movement over all-terrain

• Maneuverable– Easily moves in small spaces of 20 square meters.

• Simple– Minimal parts for easy implementation.

Objectives of Drive System

Option 1

Option 2

Option 3

Option 3 was Chosen

Key Advantages Identified in Option 3:• Zero Degree Turning Radius• Minimal Wheel Slip

Possible Technical Challenges:• Account for Minimal Wheel Slip• Provide Enough Power to Rear Wheels• Implementation of a Robust Drive System

Technical Challenges• Control Wheel Slip

– Position CoG close to Rear Wheels

– Acceleration should not exceed a = μsg/2

– μs,min,= 0.7

– amax =3.5 m/s2

• Provide Enough Power– ω = 225 rpm– T = 1 N-m

Robust Drive System

Prototype Considerations

Key Aspects• Zero degree turning radius capability allows vehicle to traverse search path

• Sensors in front of vehicle

• Ability to guide a vehicle with GPS

• Direct drive would be simple to control with feedback loop

Materials• Purchased large pneumatic casters and rubber wheels similar to final design

• HDPE used for body – strong, lightweight, machinable, and cheap

• PVC used for boom– Strong and stiff– Easily reconfigurable

Fabrication Limitations• Rear wheels should have better tread but the hub was useful

• L-Brackets are not ideal

• Center of gravity should be moved toward rear of vehicle

– Reduces caster drag– Increases drive traction

Next Generation Prototype• Use more powerful motors and battery

– Determine caster performance at high speed– Analyze repeatability of maneuvers (with a focus on caster performance)

• Explore better designs for shouldering and fastening body panels

Circuit Diagram

Circuit Diagram• 12V Motors, 355 oz-in torque failed due to unpredictable dynamic forces

• 24V Motors without specs used in place

• Determined feasible based on in-robot testing

Circuit Diagram• MOSFET transistors used as a gate to close circuit, allowing the motors access to ground • Can handle 100V, 12A

Vehicle Operation

• Record Start and Hazard Location (Sample the GPS Receiver)

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Longitude (m)

Latit

ude

(m)

2.7 m

GPS Uncertainty

Vehicle Operation

• Two Phases:

- Traverse. Use GPS to guide vehicle within 10m of hazard

- Search Algorithm. Systematically search area around hazard

Traversing• Considerations:

- Speed. Travel fast but allow GPS to acquire accurate readings

- Position/Orientation. Need to know position and orientation

- Can’t Rely on Angles. GPS error too great to accurately calculate angle of orientation

GPS Error vs. Vehicle Speed

Minimum Error at2.6 m/s

At 1.8 m/sOnly 6% greater error

TraversingN

W

S

H

• Drives forward

• Record location

• Pivots and reorients if x or y distance to hazard is increasing

• Stops when within 10m of hazard

Search Algorithm

- Square Spiral

- Never necessary to retrace path

- Covers greater than 90% of area

- 40% faster than back and forth pattern

Results - Traversing

Results – Search Algorithm

ResultsPart 2

• Vehicle can travel at 1.8 m/s (4 mph)• Video:

• When starting in wrong direction, ‘Bloodhound’ can correct course• Locate hazardous material 30-40 m away in less then two minutes• Stop within 2.7 m of original target

Feasibility / Recommendations• Proves GPS technology is feasible for the use

• Without extra technology, reckoning system is crude but effective

• Electronic compass should be investigated for future models to refine drive system

• Casters / Rear Driven wheels allow easy navigation• Motors for this type of application are readily available

• Both possible motors provided enough torque• Higher quality motors available to increase speed to

2.0+ m/s• Stationary boom adequate to search large area

Lessons Learned• Compass can be combined with GPS to create useful and accurate system. GPS on it’s own can be very precise but is not as repeatable• Infrared sensors can pick up false positives based on reflections of the sun or other objects, including the IR emitter even when the emitter is out of range

Thank you.

Questions?