Why an onager? I live in a big city, and there is not enough space to shoot any hurling device without breaking the neighbours' property. So this thing needs to be so small that it can be moved on the back of a bicycle. Torsion based catapults excel at hurling small objects great distances, while trebuchets are great at hurling very heavy ones at still respectable distances. But for a trebuchet to throw large distances, it needs to be big. This catapult throws stuff at over a 100 meters and you would need treb with a 3 meter arm to throw as far!
|Dimensions:||width: 0.24 m, length: 0.46 m, height: 0.25 m (0.071 m for the base)
thickness of the construction: 28 mm minimum
hole for the rope: 31 mm
Skein: 6 m Polypropylene woven rope (6 mm, breaking strength: 3700 N/380 Kg)
Arm: Hickory I guess (old hockeystick)
Washers: Pesca (some kind of impossible to get very hard plastic) and 40 mm PVC tube to hold it in place.
Washer plates: Pesca plate (2 mm thick) and steel plate (2mm, not in the photo)
Pouch: strong shopping bag
|Range:||well over 100 m for 10g pebbles (very difficult to determen, the pebbles are not visible anymore at such distances and it is impossible to find them back. One projectile,
fired at half power, was recovered at 77m)
About 75 m for 20g pebbles.
|Length of arm:||0.31 m|
|Length of sling:||0.20 m|
|Maximum torque:||more than 45 Nm (it takes 15 Kg of force to push down the beam)|
|Energy storage:||40 J|
The arm is almost at its maximum tension and will be replaced
by a new ash one. The sling needs to be stronger and there will be a new, winched, lever to pull the
arm down as this can not be done by hand anymore. Also, I am not very happy with the washers,
since they have started to break; I may need to replace them with authentic ones. (The romans figured this
out a while back) The release hook needs a completely new design.
Oct 23 2000. The thing is finished. All reenforcements are done and it can take a large torque. This also means the end of the project and I'll have to look for another hobby. It has been fun building and playing with it for the last two months.
Be careful: don't stand in front of it, don't put your head above it and don't stand behind it. Use a safety zone of at least 200 meters in front and 75 meters behind the machine (depending on its size). Don't park your car behind it.
And on the brighter side; don't shoot grapes at your bathroom wall; they make a real mess.