DO NOT make pneumatic rams from scratch, CO2 in any form is extremely dangerous (one of the reasons why I havent used it in my robots). You can build a pneumatic flipper, but as you are first-time builders, you MUST buy most of your pnematic parts off the shelf. I guess you do not have enough expirience to mod a scrap ram, which if not made safely would be extremely dangerous.

When building Pneumatics for the first time, look for direct help from someone with full expirience.

Cheers, Ewan
http://www.micro-maul.co.ukwww.micro-maul.co.uk