Unsmooth dolly.. how do I fix?

[mrbrycel]

My dad made a DIY dolly for me, and I love it. For the most part, its pretty smooth, but when I look at the footage I notice a slight speed change (slower, faster, slower, faster) at each wheel rotation. What do you think the problem is, and how can I fix it?

Here is what it looks like. Angle iron, skateboard wheels, PVC.

here is some footage:

http://vimeo.com/2736153

 

[Richard J. Johnson]

Try lemon Pledge on the wheels and track. I know it sounds strange. But try it. I have a similar dolly and lemon pledge works wonders.