This has always been my question. In college, we built a spinning pumpkin launching appartus...the first time we had it release a 5lb pumpkin it the whole frame (about 400lbs) jumped about 2 feet in the air a split second later.
Unless they are releasing liquid, releasing two projectiles a half cycle apart (which still isn't optimal) or something similar, I can't see how the counterweight doesn't just turn the structure into dust instantly. If it isn't perfectly the vibrations will just eat the thing.
If you could guide the counterweight, maybe you could use the thing for either forging [0] or bonding of metals [1]
Unless they are releasing liquid, releasing two projectiles a half cycle apart (which still isn't optimal) or something similar, I can't see how the counterweight doesn't just turn the structure into dust instantly. If it isn't perfectly the vibrations will just eat the thing.
If you could guide the counterweight, maybe you could use the thing for either forging [0] or bonding of metals [1]
[0] https://en.wikipedia.org/wiki/Heavy_Press_Program
[1] http://www.explosionbonding.com/