Torque and Power

Torque is how hard the motor shaft is twisting. Torque is measured in foot pounds. For example, if the torque of a motor is 1 foot pound, a 1 foot bar connected to the shaft would exert a force of 1 pound at the far end. A 2 foot bar would exert a force of 1/2 pound, etc.

Power is torque times rotation speed (RPM). A motor running twice as fast with the same torque would generate twice as much power.

Here is a simple explanation of the current torque relationship:

The load that the motor is driving requires a certain amount of torque for the speed that it is driven. Generally, the faster it is driven, the more torque that is required.

A motor has a relationship between torque and speed also. The faster the motor runs, the less the torque. This is because the torque is caused by magnetic fields, which are proportional to current. A motor acts as a generator that generates a reverse voltage. The faster the motor turns, the more this reverse voltage limits the current.

When the motor is connected to the load, it will run at the speed at which its torque will be equal to the torque needed to drive the load. If the load's torque increases, the motor will slow down and draw more current. If the load's torque decreases, the motor will speed up and draw less current.

The load has a torque/speed characteristic curve. The motor is sized to provide at least that torque at that speed, otherwise it would stall. As the load torque goes up, so does the motor current. In fact, they are proportional to each other, Boss. Same if the load torque goes down, so does the current.

Shaft power is simply torque times speed.