Building the Bot

Base: To make the base, I used a band saw to cut 7" diameter discs. The material is 3/16" thick Lexan, or polycarbonate. This material is nice to work with for machining and for it's durability. It's not as brittle as acrylic, and it doesn't scratch as much. But it is a little heavy, so if you use a lot of it, that can add up. Also, I probably could have used 1/8" thickness, but it just seemed a little too flimsy. Here's a shot of cutting the base, using a simple circle jig:

Next is mounting the motors. To make the motor mounts, I created a template on paper, cut it out and folded it to test for size and shape. I then marked the holes where I wanted them, and piereced small holes through the paper, to mark where to drill the aluminum. Here's a shot of the template, and the finished motor mount:

And here it is again, with the motor. The holes are very sloppy, even though I used a drill press. I've learned to just make all holes bigger than you need, because there will always be alignment issues if you don't.

Placing the motors: Now I just need to place the motors on the base, and mark the holes for mounting. The mounting holes will be drilled and tapped, allowing me to screw the motor mounts to the base. Again, larger than necessary holes in the mounts will allow me to align the motors after the fact, to get it to roll straight.

And here's a shot of tapping the motor mount holes, after they've been drilled. The polycarbonate is easy to tap.

Casters: The casters need to be mounted front and back, so we need cut-outs for them. This is done on the bandsaw:

Mounting the Wheels: Since the wheels have a bigger bore than the motor shaft, I figured it would be a good idea to add two set screws, for a total of three set screws per wheel collar. This way, the motor shaft could be centered inside the wheel bore. Here's the drilling of the wheel hubs:

And tapping the set screw holes:

I soon realized I also needed a shim of some sort. I was lucky and found 1/4" O.D. aluminum tubing, with an inner diameter very close to the diameter of the motor shaft. I cut this tubing, tapped it into the wheel bore, and drilled through it at the three locations of the set screws. If you look closely at the first picture of the wheels at the top of this page, you can see the inserts.

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