[utexaspunk]

I would imagine it's stepper motors and rotary encoders turning the pulleys, with perhaps some solenoids or servos to push the tops of the cans.

[ninju]

Along with some kind of Z-axis calibration to validate height (GPS or barometer based) since drift due to slippage or weight changes is quite possible

[haihaibye]

Or markers on the wires.

[SiftedTech]

Thanks both!