I read a research paper that explains why permanent-magnet synchronous motors (PMSMs) are better suited for high-precision position control than brushless DC motors (BLDCs). I'd like to buy one, but the only PMSMs I can find are very large and expensive.

Does anyone know a good source of PMSMs suitable for servomotor control?



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  • \$\begingroup\$ What's your application? Perhaps another form of motor such as a stepper motor may be better. PMSM are very expensive and hard to get for a reason! They are used in medical and military equipment.. Also shopping questions like this are not allowed on the Stack Exchange network. \$\endgroup\$ – KyranF Mar 1 '15 at 18:12
  • \$\begingroup\$ Have you got a driver capable of producing sinusoidal motor drive? If not, forget PMSMs. \$\endgroup\$ – WhatRoughBeast Mar 1 '15 at 18:14

When brushless, synchronous 'DC' motors were first introduced the stator windings were wound in two different ways: (1) such that the generated emf, or equivalently torque coupling to the rotor appeared as a trapezoidal function and (2) such that the generated emf, or equivalently torque coupling to the rotor appeared as a sinusoidal function. The motors wound in the fashion of (1) acquired the name 'Brushless DC Motor' and the motors wound according to (2) were called 'Permanent Magnet Synchronous Motors' (PMSM). But the fact is that both types of winding's are technically PMSM's. The trapezoidal wound motors I believe then were less expensive to manufacture, but my understanding is that most if not all PMSM's today are sinusoidally wound.

A sinusoidally wound motor that is sinusoidally commutated will offer the least amount of torque ripple as the motor rotates, so this introduces less jitter in rotational movement as compared with a motor that is trapezoidally commutated - using Hall sensors. But commutation either requires an encoder signal for the commutation or the smarts of sensorless commutation. If you are doing position control you'll need an encoder regardless. But your amplifier needs to support encoder input.

  • \$\begingroup\$ TI has a good summary here where they describe the details of the stator windings and the difficulties with sensing the rotor position. \$\endgroup\$ – tomnexus Mar 2 '15 at 1:34
  • \$\begingroup\$ The term PMSM commonly implies sinusoidal back-emf instead of trapezoidal back-emf. But just so that I'm clear, I'm interested in sources for brushless motors whose windings are intended to receive AC power. \$\endgroup\$ – user934904 Mar 2 '15 at 4:15
  • \$\begingroup\$ There are lot's of motor manufacturers that supply PMSM that are not all big. I've used motors from slmti.com , but even small motors are not cheap. Generally one begins with an analysis to size the motor - peak torque, peak speed, voltage, etc. But if you are just looking for a motor to experiment with I suggest you shop on EBay. There are lots of surplus stores that have PMSM's that post their wares on EBay - for very reasonable pricing - good luck. \$\endgroup\$ – docscience Mar 2 '15 at 4:38

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