A torque motor is typically a frameless motor used in an application that is mainly for torque control with at very slow or zero speed. Applying torque is a basic function of any permanent magnet motor (brush or brushless). The torque motor can be multiple phase or single phase, depending on the application. If the angle of motion is less than 30 degrees a single phase LAT, (Limited Angle Torque), device is easy to control with just two wires. For larger angles, three phase devices are more typical and can be commutated by a traditional brushless servo driver. Sierramotion customizes torque motors to the limited angle or continuous rotating applications.
Torque Motor specifications
Motor configurations are optimized to the application. “Off the shelf” motors were all originally customized to some application before they became available. This used to be an advantage with shorter lead times and lower price. This rule is no longer true, it is possible to get a custom design in the time it takes to get a “standard” product.
|Diameter range||8mm to 2000mm|
|Axial length range||10mm to 400mm|
|Torque range||0.001 NM to 1000 NM|
|Low Voltage operation||12-24 volts|
|High voltage operation||300-600 volts|
|Torque linearity||<1% error|
|Cogging torque||Minimized with zero cogging options|
Frequently asked questions
No, most torque motors are three phase machines, and others are single phase devices (with limited angle of travel). There are many motor driver options to drive torque motors. For low power single phase devices and simple home grown controller can also be made.
Torque motor diameter is not limited up to about 1 meter. At that point a modular construction is preferred for cost effectivity and handling/shipping. At the large sizes a modular arc shaped segmented motor can easily be produced.
Torque motors can me design to have through holes at 80% of the outside diameter in sizes of 100mm diameter and up. This thin radial cross section motors are optimized for thrusters and impellers where fluids will flow through the center of the rotor.
Torque motors are typically frameless and have a large diameter and a short length. Servo motors are usually a complete housed motor with a shaft, internal encoder and connectors. Servo motors would be the opposite form factor smaller diameter and longer axially.
There are elements of efficiency that are still important, like motor constant Km. If the Km is lower, the motor will have higher resistance and therefore take more voltage to reach a desired current. This can really limit things on smaller motors. Otherwise, efficiency greatly depends on speed, because power output is torque * speed and with zero speed you will have zero efficiency. The real answer is no, but you should consider the motor’s Km.