Put bearings in the tubing that fit the rod with little slop and the design will be simple and work better. If you leave the rod to work against the friction from the pvc pipes, the balancer won't be sensitive enough to be worth the effort.

Balancing props is one of those things that a lot of people are very prejudiced about. It's sort of amazing really. Some very experienced and well respected guys even take every opportunity to preach against a practice that may not be their choice but isn't ever a stupid thing to do. It takes so very little time and effort to do that you're not saving yourself much of anything by not doing it. And if you do it, you WILL find props that are badly out of balance. The practice will save you in the long run if not on every prop or even on most props. But it makes little sense to advise a beginner against a practice that has no real negatives even if the positives aren't always evident.