Siege Onager Jr: Construction

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Onager Jr: Construction
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Onager Jr's basic construction is fairly simple. I thought it would be neat to make something that didn't use screws, but after assembling the bottom, screws were needed for much of the upper frame, and for the strengthening of structural members later.

Here is half of the critical part of the frame before it was assembled. Each piece is a 2x10 inch beam. The length of the onager is 4 ft. The circular holes are for the rope bundle. Since the modiolus uses a 3 inch PVC coupling, the outer hole is about 3.5 inches across, and the inner beam has a 3 inch hole.

Here is my Dad working the throwing arm with a jack plane. It started as a rough cut piece of ash scavanged from a portable lumber mill. (It had started as a 12x12 which we reduced into many useful beams which will show up in other machines.) This beam ended up being 3 ft long, and 3x3 inches at the base tapering to about 2.5x2.5 inches.

The completed frame up on saw-horses as I coat it in deck sealer to protect it from the rain. Some of the attachments for the uprights are replaced later.

A completed rope bundle end (Modiolus and Epizygis) next to one of the extras from Balista Jr. Since the ballista needed 4, and the onager only 2, this makes a good example of how the system is put together. It is made from a 3 inch PVC coupler which protects the rope from rough edges in the wood and metal parts. There is a piece of channel with holes and gaps cut into it, plus a bit of plate steel. I cleaned the rust off two pairs, and painted them black with Rustoleum.

The completed arm with a rope wrap pressed against the breaker beam. The wrapping technique I used here failed badly. I re-wrapped the arm later, using the "Rip-wrap". After watching Bob Carbo's Onager blow an arm at the 2000 Punkin' Chunk, I thought it would be wise to use a similar technique as I read in The Book of the Crossbow, and WEAPONS: An International Encyclopedia from 5000 B.C to 2000 A.D. The theory is that if the arm hits a breaker beam evenly across it's entire length, it won't break.

Anyway, the breaker beam is a 2x6 running vertically, with a special wedge shaped piece to make sure the arm hits it evenly. This beam suffered a horrible death after about 10 shots as the arm was hitting it with the grain, and eventually axed it in half. I will be rebuilding it and adding a bit of old carpetting and metal to help the life expectancy of this critical piece.

Our first pouch. A bit of 1/4 inch line (natural fibers!) was sewn into a square of old green army tent canvas. This designed worked well after fixing Baby Onager, but on this scale, it only lasted a couple days. Another critical piece of information is that it is very important to sew the pouch to the rope, or it will slide around, and take your projectile hostage.

Additional Pages for Onager Jr
Onager Jr Onager Jr was our first torsion siege-engine of the medium scale that functioned well.
Onager Jr: Construction Onager Jr's basic construction is fairly simple. I thought it would be neat to make something that didn't use screws, but after assembling the bottom, screws were needed for much of the upper frame, and for the strengthening of structural members later.
Onager Jr : Flinging potatoes Loaded onto the car and ready for a drive to family reunion. I had finished it this morning, and the first test shot was 3 feet. How dissapointing.
Onager Jr : Rocks in Maine We rebuilt the machine, and brought it to Maine to fling rocks into the mud flats. We had rebuilt the breaker bar to be sturdier than before, and also added a winch.
Onager Jr : Upgrades After our trip to Maine, Onager Jr was used again at the 2001 History Channel Chunk, and at the 2001 Bennington High School Chunk. At the end of those two adventures, our third canvas pouch had disintegrated.
Onager Jr : Zucchini Upgrades In 2005, Onager Jr was destined to go to the zukapult contest in Ludlow Vermont. To accomplish this, Onager Jr needed to be upgraded to throw projectiles smaller than it had done so in the paste.
Onager Jr : Movies Here are some videos of the little guy in action. They were all taken during the 2001 History Chunk.

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