Electrical – Right motor for a camera gimbal and what kind of a gimbal motor is this

brushless-dc-motormotortorque

From information on the Internet I understood several things:

  1. Low KV motors are better for gimbals. For lower KV thinner wire is used with more turns.

  2. Outrunner motors have more torque than inrunners.

  3. More poles give smooter rotation and finer resolution.

  4. PMSM motors are driven by sinusoidal signal and therefore are rotating smoother than BLDC.

Please correct me if I am wrong.

So, now, this is a medium sized (60mm OD) motor from a gimbal which has very high torque. The wire is thick, its inrunner, has low pole count. All these things oppose the information above. What is going on here?

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Best Answer

  1. largely true.
  2. Often true but not universal.
  3. Somewhat true but pole shapes and drive waveform also matter.
  4. There's not much physical difference in construction betweet PMSM and BLDC. If any, it's likely to be shapes of the pole pieces.

Now what's going on with that motor?

  1. That's pretty thin wire and quite a high turn count. Moreover with 12 coils arranged as 3 sets of 4, you can get a 4:1 variation in Kv and 16:1 variation in winding resistance by connecting each set of coils either in parallel or series. I expect these are connected in series.

  2. Given the same number and size/shape of poles, the same gap, the same magnet strength, and the same winding, you wouldn't expect any difference between inrunner and outrunner.
    The outrunner version of this motor could be more compact : turn the magnetic circuit inside out and the bulky windings would then be inside and the thin ring of magnets would be outside.
    However that would leave little or no space inside the motor for an axle and decent bearings. Looks like you could stick your thumb through that space. So I guess they chose the inrunner for mechanical reasons.

  3. 12 stator poles and presumably 14 rotor poles is pretty high, it's a common outrunner configuration.

  4. For camera gimbals you probably need closed loop positioning anyway, which will compensate for lack of smoothness.

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