[lukevanoort]

As you can see from above, many materials are successful. Sanddag's suggestion is probably the easiest to work with, and M4 Sherman's is likely the cheapest of those already proposed (PVC would be cheaper still though). My team has never gone the shaft collar route (recently that is, I think some of our old robots might use them), but we've done thin-wall aluminum tubing, steel tubing, and PVC pipes. You know what we have learned? Material choice doesn't really matter much. What is more important is making sure that they are the right length and that their ends are not cut at an angle. That is why we aren't going to go with steel again--too hard to cut accurately with our tools.