One thing to consider is using ABS instead of PVC. ABS is less brittle than PVC which means it will tend to bend in situations where PVC would break. For more info about the pros and cons of both ABS and PVC check out this link
http://www.spudtech.com/content.asp?id=14
Its not exactly the same application (spud guns vs robots) but the info is still good
Hope this helps'
Danny B