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I have a small BLDC motor and I would like to use it in a project of mine.

Is there any relation between the minimum angle (precision) I can move the motor and its number of poles?

How could I calculate the minimum step I can move the motor, considering that it has 12 poles?

Thank you in advance for your answers!

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  • \$\begingroup\$ A BLDC motor in angle operation behaves rather a lot like a stepper motor. The controller will determine your interpolated angle precision. Typical microstepping is 16 to 256 of a full step (up to 200 full steps per rotation equivalent to 50 poles on a 4 phase motor) for stepper motors, standard microstepping products for BLDC motors are a bit less common or DIY so the answer is that it depends. The camera gimbal people have solved this problem a few times, check them out. \$\endgroup\$ – KalleMP Nov 19 '16 at 22:27
  • \$\begingroup\$ It looks like twelve poles. Has to be a multiple of three, doesn't it? Or does the rotor have fourteen teeth? \$\endgroup\$ – Whit3rd Nov 20 '16 at 8:19
  • \$\begingroup\$ I edited the question. The motor has 14 permanent magnets on the outer part (rotor) and 12 electro-magnets on the stator, connected to the 3 phases. \$\endgroup\$ – starScream Nov 20 '16 at 9:50
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The motor itself has virtually infinite resolution (minimum angle that it can be moved). Practical resolution is limited by the controller, which has a limited number of PWM steps.

Having more poles is better because the controller's resolution is relative to each pole. The minimum number of poles is two, which produces a full revolution from 1 cycle of 3 phase drive. Your motor has 14 poles so it has 7 'electrical revolutions' per mechanical revolution, making its effective resolution 7 times higher.

Precision is limited by random mechanical effects such as bearing friction and slop. Accuracy is affected by nonlinearities in the motor's electromechanical response. If run open-loop the rotor will not move by precisely equal amounts per step. So while you might get eg. 360 steps per revolution, they won't all be exactly 1° apart. Torque ripple also occurs as the motor rotates, so any load will cause the rotor to be pulled off position by varying amounts.

Gimbal motors are normally run closed-loop with gyros and accelerometers providing feedback, which compensates for torque loading and nonlinearities in the motor.

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