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 solution provides 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 θrθr Chassis heading, direction of travel N

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 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: $  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

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