> I was thinking of something along > the lines of compressed gas to fire it back onto some shock absorbers. > What does is average blade made of? What do they weigh? Just wondering what > kind of forces may be required to achieve this. F=mA or you need the mass of the balde x the number of g acceleration. Say the movable mass was 500 gram (~- 1 pound) and you wanted 1000 g you'd need 0.5 kg x 1000g = 500 kg or 5000 Newton. I mentioned metal-azide "explosives" - as used in air bags. Have the advantage of being fast. Which you need. Airbag in car must travel from rest to chest in time it takes for chest to travel say half distance from seat to wheel. Take it from there and compare ... Russell Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist