WRT Richards comments (an a few others) - we have to start by assuming worst case :-
1. You can impart Total KE into the oposition
2. Disc can achieve Max Possible rpm from your motor, voltage and gearing.

Of course very few will get anything this good - but there are some damn fine engineers out there who will (are) getting close.

Now - this pendulum thing. I rather like that.

If we get people to remove their disc - measure the shaft speed, and swing the disc to work out its inertia - then I think we could do a very similar set of curves showing the allowables.

I was going to work up those mass*dia^2 lines - but recognise that relies on the selection process to decide which chart to apply.

If we built a pendulum rig and callibrate it - then well only need ONE chart. Can anybody share the formulae with me (wasnt it posted here a while back ?)

Would really like to take this concept further - but finding the time is tough :sad:
Kev.