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     I am a 8th grader and I built this onager for my science fair project.  All the metal was laser cut at my dad's work.  It took about two weeks to build, just because of all the trips we made.  This compact machine launches a golf ball over 175 yards.  I am working on a better trigger system now and looking for a crank so we can go over 40 pounds of force. I am hoping to get a video up soon.
How actually did you do it ? Or isn't your creation, is it ?
I drew up a gear system on a CAD system and cut them out of metal at my dad's work. then I built the wood parts around it
OK.
I drew up a gear system on a CAD system and cut them out of metal at my dad's work. then I built the wood parts around it
rjnerd- The sling i used is 2 feet long. the rope is 3/8 in. diameter. the rope was tightened by turning a nut with a ratchet on the small gear.
Looks great! What range of sling lengths have you tried? What diameter and material are you using in the bundle? Did you pre-tension the bundle when you laid it up?
Nice , looking forward to the video!

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