This is the 1″ plastic ball caster that I ordered from Robotshop. The white ball pops out of the black holder, which has three bolt holes to secure it to the robot chasis.

I positioned the holder on the wooden platform and used a razor pen to mark the drill hole locations. Then I used my little battery operated craft drill from Michaels like so:

The bolts then went through the holder holes and the platform holes, and I fastened with the nuts so that it looked like this:

And this is what the completed mod looks like from below:

Moving from the wheel-caster chassis to the ball-caster chassis required removing and reinserting all the wires, a pain. But I tested with the square path program and it’s working. How well? Not as well as I had hoped. I think the wheels are a bit wobbly. I’ll see about getting plastic washers for them.

Now the main task is to have the Arduino convert the control codes back to turn angles and distances.