The one thing I've learned as I've really gotten into the Maker Movement is that rarely does anything work right the first time. You have to keep researching, learning, testing, and trying new things.
For example: the rubber bands that I use for tires on his tiny wheels. I had the hardest time gluing the rubber bands to the wheels. I tried all different kinds of glue, even rubber cement which is nearly perfect for gluing rubber. Nothing would work. But it turns out rubber bands are coated with a special powder that keeps them from sticking to anything, even glue and rubber cement. A quick rinse under the sink and presto, the rubber band tires can now be glued to the wheel!
Unfortunately I measured the width of the button in the CENTER and failed to account for the outer lip of the button which is a little bit fatter. No big deal. The button-wheel I measured was actually 2 buttons glued together, so I could still use a button, I just had to use a single button rather than the double I had wanted.
But there is one more issue I've been dealing with. The 9 v. batteries I've been using seem to go dead after just 4 shows. There is NO REASON for them to die that quickly. I mean, they aren't DEAD-dead, just low enough that RD-3D can't move. His lights still turn on and blink quite brightly, and he has enough power to do his "shaking" thing (which turned out to be one of the funnier jokes in the show).
When he's supposed to move across the table, I can hear his motor struggling, but he doesn't actually move. I think I know what the problem is, and I'll report back on it whether I'm right or wrong.