Small all terrain vehicle with tracks

The transmission principle:

The top motor in this picture is driving the inside gears of both differentials in opposite directions. This is the drive motor.

The other motor is driving the outside of both differentials in equal direction. This is the steering motor.

If only the drive motor is running, both tracks will have the same speed in the same direction and so the vehicle will drive straight on.

If only the steering motor is running, both tracks will have the same speed in opposite directions and so the vehicle will rotate around it's center point.

If both motors are running, one track will speed-up and the other will slow down and so the vehicle will make a turn while it is driving. The rotation point is under the slower track.

You can imagine that if the inside of a differential is driven by one motor and the other motor is driving the outside of the differential in the same direction, that the speeds of the two motors are added. If the other motor is driving the outside in opposite direction, then the speeds of the two motors are subtracted.

For Technic, this principle is also explained in "The Unofficial Lego Technic Builder's Gide" by Sariel. I build that principle using different elements and construction.

It is shown in my YouTube video: tags are: Argo ATV 8x8 Lego

Side view. The last wheel on both sides is driven, using a 0.6 reduction bevel gearing after the differentials.
The receiver is on the back and the battery box under the hood. The hood can be opened partly to reach for the on-off switch.

This picture shows the ATV on which my model is based, the Argo. This ATV is available in many different configurations.