Many thanks to our Sponsors

Bay Design

Team Carbo proudly donates to

Be sure to visit The ONAGER Store

Please send e-mails for  the team to TeamCarboLLC “at”

website design software


Onager Details

[Team Carbo - Onager] 


[Onager & trophy at PC 98] 

Onager Details

Disclaimer : Do not attempt to build this yourself. These machines are very dangerous and capable of harming, maiming, dismembering, and even killing (after all this is what they were originally designed to do when built and fired by Medieval soldiers).


Onager Construction


                            [Onager at test facility]

The 1997 Onager is poised to fling another Pumpkin at our secret testing site, where Team Carbo conducts important "high tech" Research and Developement.


                          The Making of an Onager

[Onager Plans, side view, 1998] 

The Onager is constructed with very heavy materials to withstand the tremendous stresses it undergoes when cranking it up and firing it. The frame is built out of railroad ties that are 7" x 9" thick. The frame is about 8 feet long. The arm of the Onager is an 8 ft. long log of oak, 7 inches in diameter. The torsion spring is made from 600 ft of 3/4" poly rope. The side pieces, or skeine pipes, around which the rope is wrapped have been custom built by Ray Wheeler of Bay Design in Baltimore, Md. (I had to give a plug since this is my brother Bill's company). These pieces are made from 8" diameter steel pipe each about 12" long. These pieces of pipe, which I refer to as Skiene pipes have a piece of 1" thick iron bar, 4 inches wide, running through them around which the poly rope is twisted.

[Onager skiene pipe] 

Here's the 1997 version of the Skiene Pipe (Aye, it's a manly lookin piece of iron work too!) You can see the yellow poly rope wrapped around the steel bar, which when twisted creates the torsion spring. In the 1998 version, a set of 2 steel washers have been welded around the outside of the pipe with a series of holes in them for the steel pins.


Below is a diagram of the 1998 version of the skeine pipe and pursuader bar.

[Plan for new skiene pipe] 



My bother Bill's company,Bay Design, did the above modifications with no problem, thanks to the skilled craftsmanship of Ray Wheeler.

[Bay Design logo] 



[Team prepares the Onager] 

At right, Team Carbo gets the Onager ready for another round of hurling Punkins at the Punkin Chunkin Championships in Deleware




Here is a top view of the Onager mounted on it's trailer. The winch pedaling mechanism is attached at the rear.

[Onager plans, top view, 1998] 

The entire catapult is mounted on a 2-wheel, single axle trailer allowing the Onager to be quite mobile, a definite strategic advantage in both siege warfare and Punkin Chunkin.




[twisting the torsion spring] 


Here we are ( true Manly Men! ) at Punkin Chunkin 1997 twisting up the rope torsion spring by cranking the skiene pipe with the "pursuader" bar. In the 1998 version, the pursuader bar is connected to the skeine pipe by a steel pin through 2 steel washers welded to the pipe(instead of by the chain seen in this photo).


When the skiene pipes are twisted forward with the pursuader bar to torque up the rope torsion spring( with great force and sweat), 1" thick iron pegs are inserted through the holes in the washers around the pipes and into holes in the Onager frame (to stop the skiene pipes from twisting back). Steel cable from a pedal powered winch is attached to the end of the oak arm. The arm is then winched back until it is horizontal. A sling made out of rope and leather is attached to the end of the oak arm with the projectile(usually a pumpkin or watermelon - cause they make the neatest splat when they land) in it. A release mechanism is pulled which releases the arm from the winch cable, and the forward motion of the arm causes the sling to throw the projectile.Stand back when this baby is fired - it packs quite a wallop.


[diagram of Onager shooting] 



Background and Historical Information


[model of ONAGER]         My first Catapult - "Baby Onager" - This little model was throwing golf balls over 125 feet!


The idea for this catapult came from my research on medieval weapons.  The book that really got me going is by Sir Ralph Payne-Gallwey entitled "The Book of the Crossbow". This book contains some drawings with details and dimensions of this torsion type of catapult. The author built a reconstruction of an Onager around the turn of the century, and achieved some impressive results. Once I read about this, I was convinced that the Onager was for me! In addition Payne-Galwey gives a good basic history lesson on catapults including some fascinating historical accounts.


[Payne-Galwey's catapult] 


Here is a drawing of Sir Ralph's reconstruction of a catapult which inspired me to build my Onager. You will notice many similarities to my Onager (i.e. the frame, the sling, the cable attached to the arm to winch it back for firing.)




[Roman onager] 

This is an artist's drawing of a Roman Onager. The scale at the upper left of the picture is 6 feet high, which makes this catapult almost 10 feet high, and the arm about 12 feet long. That's one mean Siege engine!

The name ONAGER comes from the Ancient Greeks and Romans who nicknamed these torsion catapults "Onager" - the translation is actually "Wild Ass" - as these machines were known for their very nasty kick!


             Another excellent source on catapult design and history is by Eric Marsden called "Greek and Roman Artillery". He also did his own reconstruction of an Onager, as well as some Balistas - another type of catapult. A more contemporary book on Catapult building is called "Catapult : Harry and I Build a Siege Engine" by Jim Paul. This book is a must for anyone considering doing something of this sort. He not only has  very funny stories to tell about his own adventures in Catapulting, but he also includes very interesting historical catapult anecdotes.       


Here's how it all began....



Go back toOnager Online home page