The intial design tried to use a limit switch to sense when we had acquired a power cube. We need to sense because the arm gets a lot heavier when we have a cube, and because we don't want the wheels to keep spinning rapidly against the cube.

The intial design tried to use a limit switch to sense when we had acquired a power cube, but mounting and actuation was unreliable. Then we found these:

https://www.adafruit.com/product/2168

we found them in stock at Mouser.

what's great about these sensors:

• they just work
• obvious color code to the wires: just hook them up to a DIO.
• pretty cheap. The 3mm ones are really cheap, but a little flaky at the distance we need for the cube intake.

Not perfect:

• Out of stock at lots of sources
• sensitive to stray IR light which could cause false operation

Since the sensor is facing towards the power cube, the cube would have to be reflecting a lot of IR for this to be a problem. A shroud over the sensor might help.

Wiring: Break Beam Wiring