Direct Drive Motors
Motors designed for direct drive operation tend to be large in diameter with a high pole count (>10 poles). The axial length is short and a large through hole aperture is common. Sierramotion designs to the application optimizing the number of poles in the rotor. Then the proper stator is selected which could be a traditional iron based stator for the highest torque output or a slotless air-core stator for optimum smoothness.
Direct Drive Motor specifications
|Low Speed||Speeds below 1 rpm are typical|
|Torque Control||Zero speed torque control|
|High Speed||Up to 30,000 rpm|
|Air Bearing Integration||Motor optimized to work with Air Bearing|
|Encapsulated Stator||Fully potted stator thermally conductive epoxy|
|Surface PM rotor or IPD||Optimized for torque or speed|
|Vacuum rated||Fully enclosed rotor and stator in stainless steel for deep vacuum or space|
Frequently asked questions
Generally direct drive motors are larger in diameter than length and have high pole counts. This can make them have higher torque than a traditional long small diameter motor. Torque output increases with diameter faster than with length
Absolutely not. The old days of using a coupling between the motor and the load prompted this limitation, it had nothing to do with the motor and everything to do with the coupling.
Yes, most direct drive motors have a large through hole that can be used for running wires or optics. The center of any motor is normally not used, except for a shaft to connect to a coupling both of which are no longer there with this type of motor application.
Yes, as long as they are electrical wound to do so. Originally high pole count motors could not run at high speed due to controller limitations, but today’s controllers have no issue with high pole count motors and higher driving frequencies.
Stiffness of a motor like this is directly related to the encoder used. If a high resolution encoder is used the stiffness can be very high.
Yes. However, response is related to torque available and inertia. Direct drive motors tend to have higher inertia than traditional motors making their acceleration less. If the direct drive motor is connected to a load that has much higher inertia (typically the case) then the response may be better than a traditional motor connected through a gear box and coupling in order to handle the higher inertia.