These are the basic type of cams. Combined with a spring (which could be surgical tubing, a pneumatic cylinder or even a normal coil spring) a kicking motion can be achieved. Just make sure you have good control of the position of the cam, so it doesn't fire too soon.
Another possible method is to use a
gate-latch mechanism (or something similar) to hold the kicker back, and release it with a pneumatic cylinder (or open the latch). This way you don't have to worry about the mechanism firing to soon.