Caterpillar track odometry model

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Short answer: You need a gyro to detect turns. Encoders are not perfect because of the he amount of slippage in turns

Then look at the encoder on each track, use the encoder value from the side that is highest to get distance traveled by that side. Assume the track in the inside is getting the most slippage.

Or use the gyro to get heading and the average of the two tracks for distance

Also remember that tracked vehicles can go up and down step slopes. f tracking position in X,Y remember to project the slope onto the plan using cos(slope)