We ended up keeping the system as a "Plan C," since the BaneBots motor on the shoulder of our arm burnt up the night before shipping, and we weren't sure if we could get the new gearbox to work at the San Diego regional. However, in testing, we did find that we needed "purge valves" on each line to the cylinder, since we would be trapping atmospheric pressure in the cylinder, preventing movement. Since it wasn't technically pressurized, it was still a legal setup. We haven't actually implemented the system in a competition. Our motor/gearbox setup has worked through two competitions, so far (San Diego and LA), so we haven't seen a need to change it out, despite the fact that the pneumatic system would be lighter and easier to control. However, this was an interesting learning experience, and I hope to implement something to this effect in next year's competition.
EDIT: I created a
PDF documenting the process of designing our system. I thought you guys might find it interesting.