[Jon Stratis]

Depending on the forcespeed requirement, look at robot designs from Arial Assist (the 2014 game) - a whole lot of robots that year utilized a catapult to launch the ball, which is just an arm doing a swinging motion vertically instead of horizontally. Some were pneumatically driven, others utilized springs or surgical tubing/spear gun tubing with a motor to pull it back, and others used a motor to drive the arm directly. Even if that's faster than you want, you might get some useful ideas from those designs, all you'd need to do is slow them down!