Actually, Ive been wondering about aiming at 200kg and sticking one big ram on the bottom (see some of MITs work in dynamic balance in the 1980s). Since the CO2 weight doesnt count, you end up significantly over 200kg (youd need quite a lot of cylinders in it). Armour it a lot, stick some spikes on the bottom, and drop on people. Allowing for some elasticity so you dont need to re-fill the ram on each bounce, I reckon it might be possible to keep it going for the full time (but Im not basing that on very much).

Shouldnt be that difficult, and if you can jump to 2m or so youre doing 14mph at the time you hit - equivalent to some rammers. You just have to take a bit of care that no-one knocks your leg off, and that you can get up in the air quickly when youre grounded.

It might well damage the arena (especially with downward pointing spikes) if you missed (the foot should be okay), and - more importantly - leap over the edge, though. You dont want 300kg hitting the outer wall at speed. Plus you need some way to enter the arena without crowning yourself on the entry door.

Id be interested to see it done; I have more interesting designs which Id rather try first.

My tuppence worth.

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Fluppet