Calculation of motor torque

Let's calculate the torque required to move the robot:

1. Number of wheels = Four wheels including two caster wheels.
2. Number of motors = Two.
3. Let's assume the coefficient of friction is 0.6 and radius of the wheel is 4.5 cm.
4. Take the total weight of robot = weight of robot + payload = (W = mg) = (~100 N + ~20 N) W= ~ 150 N, whereas total mass = 12 Kg.
5. The weight acting on the four wheels can be written as 2 * N1 + 2 * N2 = W; that is, N1 is the weight acting on each caster wheel and N2 on motor wheels.
6. Assume that the robot is stationary. The maximum torque is required when the robot starts moving. It should also overcome friction.
7. We can write the frictional force as robot torque = 0 until the robot moves. If we get the robot torque in this condition, we get the maximum torque as follows:

• • µ * N * r - T = 0, where µ is the coefficient of friction, N is the average weight acting on each wheel, r is the radius of wheels, and T is the torque.
  • N = W/2 (in the robot, actuation is only for two wheels, so we are taking W/2 for computing the maximum torque).
  • Therefore, we get: 0.6 * (120/2) * 0.045 - T = 0
  • Hence, T = 1.62 N-m or 16.51 Kg-cm