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Baby Onager was constructed in preparation for building a mid-sized onager. The basic torsion engine design was taken and improved from my Baby Ballista model. I'm going to recycle metal parts from Ballista Jr to build a mid-sized onager based on this design. If that works well, I may build a second for use in winter snow ball fights.
Baby Onager is two feet long, 15 inches tall, with a 17 inch throwing arm. Base construction is pine 2x4s, with 2x2s holding the upright up. Ferring strips were used for the angle bits.
Also part of the experiment is where to brake the arm. The 2x4 arm brake is easily removable and replaceable using wing-nuts to aid in experimentation.
Note the pouch is tied on a short distance from the release hook. This is supposed to add top-spin to the projectile to aid in distance throwing. The technique worked well on our large trebuchet Juggernaut and Juggernaut2 but I suspect it doesn't do to much at this scale.
Most machines have the trigger run through a loop beneath the arm. I ran the trigger over the arm due to the simplicity of this design. When the large machine is built, it will probably not use this technique.
These are the first set of PDF plans I've made for any of the machines. I get a lot of questions about this little onager, and now you can build one exactly like mine. My recommendation is that you can use these for ideas, but really, there are a few problems with this design you may be best off to design your own.
Unlike the pictures above, I have since replaced the arm break bar with something thinner than the 2x4 mentioned. It allows the arm to swing farther forward.
You should be able to cut the whole thing out of a single 8' 2x4, or even one of those cheap 80" framing beams. You'll need a saw, vice, and drill, with 1 1/8" bit, and something a bit smaller for the bolt holding on the stop bar. You will also need a chisel and hammer to cut out the mortises.
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|Last Modified: 11/26/16|