The Definition of Torque
First let’s clarify that force and torque are two different things. Force is when you push or pull on an object, whereas torque involves the rotation of the object. By definition, torque is the measure of a rotational or twisting force. This means when you try to turn something around an axis, you are producing torque. An example of this would be using a screwdriver to turn a screw. If the screwdriver is easy to turn, only a small amount of torque is needed to turn it. If it is difficult to turn, a larger amount of torque is required. However, torque doesn’t require movement. If the screw you are trying to turn is rusted and won’t move, torque has still been applied in the attempt to turn the screw.
Torque and Motors
Motors are used to turn something, producing torque. They can directly drive an object or create rotation through a sprocket or chain. When choosing a motor, it is necessary to know how much torque an application needs to have in order for the motor move a load or operate as needed.
A high torque example would be a residential chair lift when the motor is started while a person is sitting in the seat. This high amount of torque will rotate the motor and lift the rider up the stairs.
A low torque application would be a conveyor running with a light load on it, such as empty bottles. There is not much weight on the conveyor, so it doesn’t take much force to get the motor to rotate.
How to Determine Torque
Torque is determined by multiplying force and distance.
Torque=Force x Distance
Let’s look at an example. In Figure 1, the distance (x) equals the radius of the circle and the force (f) is the weight pushing down on the circle. The amount of torque (T) needed is found by multiplying the two variables.
One variable to take into account when calculating torque is the distance of the “lever” being used to exert the force. The longer the “lever,” the less torque required to turn an object. When you apply direct torque to an object, such as a threaded nut with a short-handled wrench, more force will be needed to twist the nut than if the wrench had a long handle.
For a given speed, the more rotational torque used, the more power supplied to rotate the particular object. With motors, this is applied when an application needs to lift, roll, spin—or any other movement that has a circular motion. Torque is often one of the most important design inputs, but other important factors to consider when specifying a motor are voltage, speed and power.