Team Mejor – The Spyder

Critical Design Review

-12/7/04

Team Mejor

Perry Smith - CAD Supervisor/Machinist Mike Ryan - Fabrication Supervisor Brian Shula - Electronics/Controls Engineer Dave Millar - Chief Engineer/Controls Specialist Ryan Sienko - Team Leader/Machinist

Special Thanks Dr. Stanisic Dr. Batill Mr. Brownell Dr. Schafer Mr. Craig Goehler

Opportunity DOD interested in detecting live mines Computer images of 20’x 20’ areas give

locations of “hotspots” Sniffer technology has been developed to

confirm or deny the true identity of “hotspots” Team Mejor has been charged with creating a

device that can autonomously use the sniffer to check “hotspots”

Requirements Device locates 4 hotspots, reports hot mines Must not set off mines Must find the mines autonomously Back Portable Weatherproof Budget: goal $400, maximum $500 Time constraint: 14 weeks

Design Issues Greatest problem - autonomous position sensing Compasses and shaft encoders too inaccurate for

dead reckoning Considered infrared and ultrasonic rangefinders

but cost vs. accuracy made ideas unfeasible Cheaper, more

mechanical solutionprovides sufficient accuracy

Spool System Encoder used on spool

measures distance from post at origin

Radius and angle to each mine is given

Rotations of spool correspond to radial position of “Spyder”

Torsion spring in the spool keeps the line taught and off the ground with minimum 0.5 lb tension

Spool System Turntable bearing allows the

top portion to rotate and always be facing the origin

Potentiometer attached with chassis measures rotation of spool system

This information along with heading from compass on the chassis gives angle from post

The deviation angle or error for this system was modelled to be only 1.5 degrees

String direction

θr

Chassis heading, direction of travelN

Spool System

Mobility Design 2 front wheels driven by two 12V motors Caster is dragged behind Motors are mounted on bottom of chassis

Mounted with Aluminum braces Encased in Lexan Connected to shaft with vertical spring pin

Shafts supported by bearings are connected directly to the 8” wheels with horizontal pins

Mobility

Features and Capabilities Uses input from keypad to move toward mine Able detect heading with compass Detect distance from origin post with encoder Can drive an arc at specified radius from post Drives to live mine and stops when mine is

detected Video

Strengths With better sensors the system will be very

accurate and consistent Mobility

Zero degree turning Appropriate speed with high torque Simplicity and quality of motor connections

Three sniffers stop motors before an accident could occur

No error propagation

Strengths Aesthetically pleasing

Symmetric layout of parts Under budget: $375.65 Quality manufacturing of parts for low cost

Acquired from Physics Lab Excellent functionality of machined parts

Easy user interface Only minesweeper to reach hotspot without

human assistance

Shortcomings Complicated assembly

220 fasteners 88 parts excluding fasteners

Motor magnets interfere with compass Steering and driving are coupled, better to

separate Electronics difficult to access in small box

Outstanding Concerns MiniMax microcontroller

Floating point operations not available Insufficient memory Little documentation/example code available

Original control logic depended on arctan function, not available Less efficient control was adopted

Consistency of encoder was unacceptable Accuracy of compass was less than expected

Spyder

Spyder

Q & A Thank you for your time. We will now take your questions.