Navigating the Robot Field

gilligan_skipperWe have talked about navigating the field for the Robot Game.  Here is a summary of a number of factors we discussed in our meetings and some links that go into depth.  There is a lot of great information on these specific issues on the FLL boards too.

1) Wheels/Coasters: 

– Larger diameter: faster and possibly more accurate measure of distance

– Wider tires:  better grip and less linear slip/error, slightly more error turning

– Bare rear wheels or coasters to minimize turning error:  coasters more accurate turning vs wheels more accurate linear driving

2) Motor Matching / Characterization:

– Calibrate to pick the 2 best matched of the 3 motors to power wheels

– Should run tests to calculate approximate linear/angular errors over various distances, degree turns and power levels.  Try to optimize by minimize error in rotation/linear movement without slowing the robot down too much.  Try to compensate for consist error/drift in movement in software if reasonable and able to do so

3) Chassis Design:

– Low center of gravity

– Wide wheel base without losing ability to navigate around obstacles

– Center of Mass in center of wheel base or slight forward over powered wheels (must include calculations of weight redistribution due to attachments and payloads)

– Side Rail(s) and Rear Bumper for alignment with walls

4) Line Following: ( simplified overview )

– 2 or 1 color or light (much cheaper) sensors placed in front of each wheel or centered in front

– Close to the mat but not too close to become entangled

Calibrated to color and ambient light

– Shielded from ambient light and recalibrated for each location, time and lighting condition

– Pick from one or several programming algorithms depending on number/location of sensors, mission, location, straight/curved mat lines, speed requirements, etc

 5) Dead Reckoning:

-Calculate expected linear distance based upon #rotations x wheel circumference [=2(pi)*r]

– Calculate expected degrees of turn based upon rotations and directions of each motorized wheel

– Experiment, measure and correct for systematic errors (eg motors, wheel friction, battery level, accumulated errors over greater distance/turning arc)

– Is the ultrasonic sensor worth incorporating as one of our four sensor input ports?

6) Truing to Compass Points:

– eV3 gyro sensor would be best, we don’t have one

– how to design to align left and/or right side of robot to wall

– how to design robot to align back and/or front of robot to wall

On a sad note regarding cultural preservation, probably no one on my FLL team probably even recognizes the fearless crew pictured above.  Did the beatnik ever get off that island?.


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