[NickE]

1) PVC is not pressure rated for compressed gases. If holding compressed gasses, a PVC failure will be violent and explosive. For this reason among others, Team 254 chose metal barrels and pressure rated air tanks for Shockwave and was very happy with this choice. If you're looking for something simpler than the welded construction we used, others have had success in the past with steel pipe. If you're just looking to do 2 barrels, it probably makes sense to skip the revolving mechanism and simply have one valve for each barrel. Keep in mind that high performing and safe valves are expensive. We went with a 1" NPT MAC Valve.

2) If you already have a mobile drivebase, you could probably build a very simple cannon in ~3 weeks if you work hard depending on how much custom construction is done.

3) For all of the piping, tanks, valves, etc, you're probably looking at slightly under $1000 to build a good, safe, cannon but you'd have to price it out depending on what parts you decide to use and which you already have. If you don't already have a set of electronics and a drivebase, the price would jump significantly.

Good luck and feel free to contact our team if you have any questions. Contact info is at team254.com. Just be sure that whatever you build is completely safe so you won't put yourself or others at risk.