We built a pneumatic catapult for RI3D on 'Snow Problem. We used a pair of 0.75" bore 7" stroke cylinders with high cv valves (Norgren v60). The black tanks are at 60 psi. The catapult is gravity return, top of the cylinders are left open. The distance from the pivot point to the piston mounting point is 6.5". The length from the pivot to the center of the cradle is 20.5". I would be happy to answer any questions.
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