This looks interesting and could be very versatile!
My thoughts:
- Rotation of the winch: I would put the rotation of the winch bar "towards" the frame. If you would put it in the "usual" direction there is the danger of tipping over the device at high elevations. Otherwise you could also charge it before erection.
- Method of charging: With a usual onager you can attach the winch cord at around a 45 degree at the lever. With this design you have lift the lever a bit by hand first. Otherwise the winch will not pull in the right direction. You also run into trouble that you will move the position of the lever in the torsion bundle longitudinally as well as laterally, as the winch will pull at a really bad angle during the first 90 degree.
- Make the stanchion / the legs so, that it can be fixed to prevent any movement. When you fire the device I think that the stanchion will first be lifted upwards and then pressed into the ground (conservation of angular momentum during the first period of the shot and in the second period absorbing the impact of the lever).
The stanchion has also to be quite stable as it has to absorb the whole impact energy of the lever.
Edited: This statement is actually wrong. The stanchion does not have to absorb the impact energy of the lever but only some momentum gained during the throw. It's not that much.
- To allow for a near-to-180 degree rotation of the lever you have to make the stabiliser bar at the torsion bundle either quite flat or place it further away from the torsion bundle as it is desirable.
- Performance of the torsion bundle: A torsion bundle is not really linear in force. Therefore at low twist you will have not much force while at full twist the applied force will become way higher than expected from the first half turn. Well, at least that is what I experienced with my little onager
.
The biggest problem will be the charging/the attachment of the winch. If you operate it at low power (charging "by hand") you will certainly be able to shoot it. But if you go to higher powers you will run into massive problems to find an adequate charging/winching mechanism. One could think about something like deflection pulleys, but that would require a quite sturdy additional frame for them...
Good luck and let us know how the project goes!