medieval ball buster
On a thread about self busts a forum member posted a picture of a ball busting machine. The only trouble with the one shown was that you manually pulled it back and then released. I was possible if you were doing this yourself to let up on the pull. Chickening out as it were.
I've thought about building a small onager, modified for the purpose of BB, either ones self or under the control of another, just been too lazy to do it. Plus the need isn't there at this time.
You can see the basic principle behind the medieval war engine from the pictures on the linked page at http://www.onager.com/. These are of a small model which could be scaled up easily enough. The arm is pulled back and put in a cocked position. The "trigger" is the pulled so no tension can be let off at time of release. A trigger could also be made using a cotter pin with a string put through an eye bolt screwed into the back side of the arm. The cotter pin could also be pulled out by a solenoid controlled by ??? Look up trebuchet models on google to see what I mean about a trigger.
It could be designed with the top being a seat and the victim can sit facing the arm or turned around backwards with the balls hanging down in the line of fire.
The motive force applied in the torsional war engine was traditionally many windings of a cord between the sides and the torque could be adjusted by twisting one of the end caps. On this model it looks like they might be using some rubber tubing? Your imagination could be used as to what to put on the end of the arm to do the kicking.
Let me know what you think.