Description

	Each track is driven by a separate motor with worm and wheel gearing. It moves slowly, allowing good straight line tracking and predictable steering correction.
The left side small-link chain drive is 'overslung' as shown on the right.
	The right side chain drive is 'underslung'. The purpose of this is to have the two drive motors running in opposite directions, yet have both tracks moving forward.
The drive shaft extensions meet in a differential. The purpose of this is to sum the shaft rotations. If the two were running at the same speed and opposite directions the casing would not turn at all. But they never do. Unequal friction and/or motor characteristics have one or the other running slower. Therefore, the casing does turn, very slowly. The differential is well supported; however, it does not support the weight of the model, and is used for control purposes only.

	The differential casing engages a gear on an encoder (rotation counter). We measure it in increments of 22.5 degrees. We use that to correct for unequal drive train characteristics. Note that the step-by-step assembly shows two 8 tooth gears instead of one 16 between the casing and the encoder.
A front view shows two pulleys at the end of the motor/worm shafts. They are not 'headlights'. They allow you to see the steering corrections as the motors 'step'.