Kaz and Lina's Onager
A second in our documentaries of SCA combat siege
construction. This onager is designed as a companion piece to the
Bird of Prey, our combat ballista. It is a torsion engine,
by a cord skein. It has a period cocking mechanism and can be
strong enough to throw actual payload as well as combat 'rocks'
The same primary considerations applied as when we
a design for the Bird of Prey. Mobility was not as important as
durability, transportability and appearance. So with these things
in mind, we decided on a scale of slightly larger than 1:2 for
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,
4x4 and 4x6 sizes were used throughout. The treated lumber was
because we knew that we would be storing the engine outdoors quite a
(like the Bird), and with a good stain it is both weather and parasite
Here is a picture of the finished engine - it is
impressive. It works well with both 1 pound combat rocks and 4
clusters, as well as doing an impressive job throwing water-filled
milk jugs for static (non-combat) demonstration
The materials needed to build the frame of the
These are 4 x treated landscape timbers. You will need 3 - 12
4 x 6 and 1 - 8 foot 4 x 4.
A side view of the onager built by Sir Ralph
This engine is well represented in his book "The Crossbow", these
are from that book. The Onager as shown measures 10 foot 6 inch
length. We scaled our engine to fit in our van - it is 6 foot
A front view of the onager - the original was 6
between the rails, our engine is 4 foot outside dimension.
Rear view of the engine - the original was
of 12 x 18 timbers for the side rails and the front brace, and the
The rest was no smaller than 6 x 6, and the winch roller was 7 inch in