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Possible Duplicate:
Torque Required For a Motor to Move an Object on Wheels?

I want to build a 4 wheel robot. the maximum weight of the robot is approximately 100 kg. and the radius of my wheel is 150 mm (outer dia 300 mm and inner dia 280 mm)** and the width of the wheel is 120mm. I want to use 4 motors in 4 wheel in order to run my robot. this robot will run on a very rough surface or the sand like surface. Can anyone pls tell me what is the required torque of every single motor? If I want to use 2 motor to run the robot then what will be the case? If anyone can suggest a formula for calculating the torque it will be helpful.

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marked as duplicate by Chris White, ja72, Manishearth Jan 28 '13 at 5:38

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

The simple answer is that no we can't tell you what the required torque is, because we don't have enough information.

The are two things you need to consider to determine the required torque. Firstly what acceleration do you want your robot to have? From the desired acceleration and the robot mass you can work out what force you need at the point the wheel touches the ground, and this force times the wheel radius gives you the torque. This also determines the ability of the robot to climb slopes since you're opposing the acceleration due to gravity.

Secondly you need to work out the force needed to overcome energy losses as the wheel rolls over the surface. For a smooth hard surface like glass these will be minimal, but if you're driving over sand you'll probably lose a lot of energy. I think the only good way to find out what force is needed is to try it. Drag your robot over sand and see how much force it takes. Then multiply that by the wheel radius to get the torque.

Torques just add, so the torque per wheel is just the total torque divided by the number of wheels. Likewise if you have two motors the torque per motor is the total torque divided by the number of motors.

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