hi all iam trying to find out what gearbox and chain drive spocket sizes i need for this to push a load of 4 ton anyone have idea of what i would need.
adam

Depends on torque/speed rating of motor, what the gearbox ratio is, how fast you want to push it, is the load on wheels/rails/nothing, uphill/downhill?

its needs to go at about 3 mph and it will be free running until it pushs the load and its all on flat ground.
adam

Need to know rated speed of motor and gearbox ratio. At a guess though - if you wanna push 4 tonnes with an 800 W motor - i'd say you want the smallest damn sprocket you can get on there!

Liam

Put a torque wrench on the hub nut of the wheel (if you can) and see how much the turn over torque is to move the 4 tonne load.

If you know the starting torque of the motor you could work out the sprocket sizes based on torque ratios.