Need a solution -- converting a translatory motion into rotary

[monster_head]

Can anyone suggest me a mechanism which can provide me a good rpm when I'm converting a translatory motion into rotary one. I've crankshaft in ma mind. The load is of about 250 kgs and its loaded on a panel and I need to convert that linear downward motion into rotary and with a good rpm. And even have made calculations for rack and pinion. But ain't gettin the speed.. Badly need help with the design..

 

[slashragnarok]

The smaller the pinion the faster it'll spin (more rpm). What will you use the rpm for? Is the 250 kg load reciprocating or is it just a one-time downward motion?

 

[monster_head]

its is a reciprocating 1. I'm using springs to provide a recoil to the panel. apart from the energy absorbed by the spring i need the it provide me the spin. I'm using gear trains to maximize the speed. but its totally depended on the displacement of the panel due to the load and the spin provided by the its displacement

 

[Mech_Engineer]

What's wrong with a crankshaft like in an engine?