not to be pedantic, but this is a pretty clever approach to the wheel bumps causing problems. no need to rock the bumps out!

Porta-Glide Dolly Sleds

I built a skateboard wheel tripod dolly that runs on PVC pipe and I have to say it's a bit pants. I think the PVC is prone to warping and moves as the dolly rolls over it and getting skateboard wheels that will run smooth ebough isn't easy. I found after doing ten takes I get one useable shot, due to jitters on the other shots. And the useable shot isn't great either.

I might try running it on metal pipes, Reinforcing the chassis and getting some higher grade wheels - I used wheels off really cheap skateboards that were about £9.99 for the whole skateboard.