How much torque do I need?

Question by JWD: How much torque do I need?
Wanting to build an electric wheelchair. How much torque do I need in order to move 400 pounds?

Thanks!


Best answer:

Answer by Sassafras
You haven't provided enough enformation to provide an adequate answer. On a smooth flat surface with very good bearings and wheels 1 foot*lb could "move" 400 pounds, but it would accelerate very slowly.

On a more practical level you might consider the steepest grade you want to have the wheel chair negotiate. For example to climb a 10 degree slope you could calculate required torque like this:

Assume:
wheel diameter = 2 feet
Frictional losses are minimal
Acceleration at maximum slope is not needed


Calculate minumum force to climb 10 degrees with 400 pounds:
F = 400 sin 10 = 69.5 lb

Now calculate the torque required on the wheel to get that force at the tire:

T = F*r = 69.5 lb * 1 foot = 69.5 ft*lb

So you would need a minimum of 69.5 ft*lb of torque to move 400 pounds up a slope of 10 degrees. I hope this helps.

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