Kaz and Lina's Onager


A second in our documentaries of SCA combat siege weapon construction.  This onager is designed as a companion piece to the Bird of Prey, our combat ballista.  It is a torsion engine, powered by a cord skein.  It has a period cocking mechanism and can be tensioned strong enough to throw actual payload as well as combat 'rocks'

The same primary considerations applied as when we chose a design for the Bird of Prey.  Mobility was not as important as cost, durability, transportability and appearance.  So with these things in mind, we decided on a scale of  slightly larger than 1:2 for the engine (compared to the engine dimensioned in The Crossbow).  This would allow the frame to fit in my van with only minor disassembly, and still would give it enough size to be an effective power source.  The frame ended up around 6 foot long and 4 foot wide.

We chose to make the engine out of treated lumber, stock 4x4 and 4x6 sizes were used throughout.  The treated lumber was used because we knew that we would be storing the engine outdoors quite a bit (like the Bird), and with a good stain it is both weather and parasite resistant.

Here is a picture of the finished engine - it is quite impressive.  It works well with both 1 pound combat rocks and 4 tennis-ball clusters, as well as doing an impressive job throwing water-filled plastic milk jugs for static (non-combat) demonstration



The materials needed to build the frame of the Onager.  These are 4 x treated landscape timbers.  You will need 3 - 12 foot 4 x 6 and 1 - 8 foot 4 x 4.


A side view of the onager built by Sir Ralph Payne-Gallwey.  This engine is well represented in his book "The Crossbow", these drawings are from that book.  The Onager as shown measures 10 foot 6 inch in length.  We scaled our engine to fit in our van - it is 6 foot long.


A front view of the onager - the original was 6 foot between the rails, our engine is 4 foot outside dimension.


Rear view of the engine - the original was constructed of 12 x 18 timbers for the side rails and the front brace, and the uprights.  The rest was no smaller than 6 x 6, and the winch roller was 7 inch in diameter.