I am just completing the plans for this:
An Onager made from 4X2 along with other materials. Its the same concept as the tennis ball ballista and requires moderate wood working skill as well as some power tools. It will be an excellent project for schools or youth goups with adult supervision and will be a commerical item at $10 for a PDF format plan and instructions.
I need one person to proove the plans. That means they get a draft set of plans and instrructions and use them to build the machine as designed within a short period of time. Not they get a set free plans that they share with all their friends and I never hear from them again. that would annoy me.
So if you are fairly handy with a drop saw and a dril let me know in the comments and we’ll see who is first.
Please note this machine is designed to be a moderate power and throw tennis balls as an educational device. You wouln’t be knocking down walls with it or throwing bowling balls. You will however be able to throw a tennis ball into the fairly small area with every throw.