Which type of motor/controller can maintain the smoothest and most constant speed in the range 300 - 1000 rpm with minimal vibration? ie: low cogging torque, etc.

I have an application in mind which requires spinning a 100mm diameter 0.5kg static load.

I have been advised to consider the following options, most of which I know nothing about and need help deciphering them:

  • sensorless low kV BLDC motor with FOC control
  • PMSM with space vector modulation
  • high current control bandwidth
  • HAL sensored brushed DC motor with many (odd numbered) commutators
  • encoder with high current control bandwidth
  • rhombic winding

One example development guide can be found in microchip website and video demonstrations of similar setups here and here

  • \$\begingroup\$ I don't know much about this field, but I do suggest that you add a few more actual requirements. How smooth does it need to be? What's the tolerance on the RPMs? What sorts of constant and variable torques do you expect? And, what's the budget? Would a very heavy platter on very good bearings driven by belt be a good solution (like phono turntables), and if not, what spec makes you dislike it? \$\endgroup\$ – gwideman Mar 21 '14 at 8:31
  • \$\begingroup\$ Sorry, should have been more specific. My application is a spin casting machine. In my case, the surface quality (optical clarity) of the cast is dependent on the smoothness of rotation.I require average constant torque of about 14mNm to rotate the load, Although I'm not sure about starting torque. The motor will spin a shaft with tapered bearing assembly and timing belt. A heavy platter, or fly wheel may require a more costly, powerful motor. \$\endgroup\$ – MachuPichu Mar 27 '14 at 3:58

Without more info it's hard to do other than generalize, but for low torque ripple a permanent magnet sinusoidally wound BLDC (synchronous motor) with position feedback from a resolver or high resolution encoder and a driver that creates true sinusoidal excitation (via conventional/FO control using SVM or 2 phase current feedback PWM) will give smooth torque and low torque ripple.

Avoid trapezoidally wound BLDC motors, hall sensor feedback, switched reluctance motors, and sensorless commutation schemes (unless you know they perform very well with your particular motor in your speed range of interest.)

| improve this answer | |
  • \$\begingroup\$ Thanks John, I have been recommended this Maxon HAL sensor combined with this DC brushed motor, why should I avoid HAL in this case? Can you recommend a particular supplier/brand of motor? \$\endgroup\$ – MachuPichu Mar 27 '14 at 3:58


  • PMSM sinusoidal wound, simultaneous 3-phase injection (hand wound motors, provides the most balanced Back EMFs)
  • feedback with commutation done through resolver or HED/encoder combination (resolvers are the most accurate, but an HED/encoder combination can be pretty accurate depending on the resolution of the encoder. with the encoder, HEDs are necessary to find the initial position of the rotor upon start up as it is not guaranteed that the index line of the encoder will be in the right location.
  • feedback is necessary (not a sensorless motor) to maintain a constant RPM. Without feedback the rotational speed would drop the moment the rotor makes contact with another surface. This is because, without feedback, the amplifier has no way of knowing when to supply more or less current to maintain a given speed.


  • SVM (Space vector modulation) is recommended because it maximizes the efficiency of the amplifier, allowing it to use more of the available bus voltage.

  • 3 phase current feedback is recommended. This means that a sensor is located on each phase to monitor the current and report it to the control card. Actual feedback loops on the control card are usually done with only two phases (A and B) because the 3rd phase can be derived from the first two mathematically.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.