Originally Posted by neilL
Looks really good for a prototype!
How about a simple (and cheap) calibration rig to go with it? Something like a pendulum with an indicator arm (the sort that stays at the max swing when the arm swings back) so the fixed rod can be placed against a plate and the firing rod can then strike with a known max energy. Set so that the max energy is equivalent to a pellet landing at 50m which started with the max (e.g. 11.5ftlbs or whatever) e.g. your 5.5ftlbs.
Yup, some method of calibrating the device is definitely something that needs to be developed.
Using a device to calibrate the kinetic energy is not the correct way to go though.
The reason for that is to do with Momentum Impulse theorem and the differences between elastic and inelastic collisions.
So it's momentum and not kinetic energy that is the important measurement in the collision.
It's an open source community project though, so anyone and everyone are very welcome to contribute - I'm not that great at theoretical physics having kinda stopped doing any of it when I left school 30 years ago, but I'm sure there are people around who know what they're talking about. Simon Ayres? - I bet he'd come up with a clever way to calibrate them.
My current method is to calibrate by practical testing to make sure it gives the same results as shooting a killzone with a 5fpe pistol. The collision isn't the same, but I think I can get a close approximation of the effect by just fine tuning the power output. Once I've got the output about right and it produces the same results as a pistol, I can possibly use something to measure the momentum and use that figure as a benchmark to set up other devices.
Ideally what I want is a really simple standard test that's cheap and doesn't need any specialist tools.