This is a proof of concept for a 2-setting automatic K'nex transmission. This mechanism is not intended for use in any future project, I simply had the idea and wanted to see if it would work. The wheel on top of the mechanism spins continually in one direction until its movement is interrupted. The machine detects the rotational force applied on the axle and automatically switches gears, reversing the direction of the wheel to avoid stress on the motor.
This machine was designed and built in about 4 hours from nearly 500 pieces and 33 gears.
Video of the mechanism in action:
Close-ups of the switching mechanism: