What is the difference between starting and stall torque? In reality they are the same, it is just how they are interpreted by the application specifications.  Starting torque is the maximum torque that can be produced by a motor in order to start rotational movement of the load. Stall torque is the maximum torque that can be applied to the shaft and cause the motor to stop rotating. When there is no rotation in the motor, the wound coils are acting as a fixed resistance. Ohm’s Law states that current is equal to the supplied voltage divided by the resistance. This would be the starting/stall current.  If the motor’s torque constant (K_t) is known you can take K_t* the current and determine the starting/stall torque.

Make sure you keep in mind the conditions under which you want to understand the starting/stall torque. A “cold” motor will have higher torque than a “warm” motor. Heating of the motor causes the resistance of the windings to increase and the residual flux in the magnets to decrease. Thus reducing the start/stall current and changing the torque constant.

What if you are using a motor control that limits the peak current to the motor? If the current is limited to some value below the manufacturer’s advertised starting/stall current, you will not be able to generate the advertised starting/stall torque. Remember that torque is proportional to the current. You need to make sure that you can supply enough current to reach the torque required to start the load.