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what kind of motor do i have/need?

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--- Quote from: ElectroNick on December 09, 2011, 01:47:54 PM ---Speaking of various BLDC motors: that's the size I like!  ;)

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Now that is just COOL!


--- Quote from: ElectroNick on December 09, 2011, 01:13:02 PM ---It sounds like you need an outrunner motor (the one where the permanent magnet shroud rotates around fixed windings core) and it looks like it may be the ones specifically targeted to helicopters that you're looking for (larger diameter shroud, higher torque, slower RPMs).
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Actually, the inrunner ones I think would be better from a safety standpoint. With the outrunner you can get something to drag against it if you aren't careful. The HiMax motor I have is an inrunner motor.

Another question for you while I have you here. The HiMax motor was described to me as a stepper motor, any idea why that would be? I was told that this stepper motor just uses PWM to drive it with the pulses at a high rate from the speed controller so that it spins fast. Did I miss something in that description? Is a stepper motor in the end just a normal BLDC? If I go with a "stepper" motor am I doing myself an injustice in efficiency or life span of the motor by running it at a contstant speed for a long time?

Well, yes, steppers are just another kind of a BLDC motor. They are wired differently than the three-phase ones and basically are more suitable for  low speed (including very low speeds in microsteps) and high torque applications as well as those applications that require holding the position.

You can use a three-phase BLDC motor as a stepper (of sorts) - it has 36 steps per revolution if designed as a typical DVD spindle motor. But you cannot use steppers as three-phase motors. Besides, many steppers have 100+ steps per revolution, so they allow for much more precise control. Also, since steppers are able to hold position better, they are very often used without any rotational feedback whatsoever. They almost never have Hall-effect sensors built in and the stepper controllers (at least on the low end) don't use EMF feedback because they "trust" the stepper to respond exactly to the step commands. This of course assumes that the stepper was sized correctly to the torque required for the application.

By the way, I contacted Castle Creations regarding what kind of feedback their controllers use and they responded that they do in fact use EMF feedback.

Anyhow, I would say that you may look at steppers instead of three-phase BLDC if the RPMs are low (or very low) - you may be able to eliminate the gearbox.  On the other hand, they may not be as well suited for long time runs. They do work OK for hours on end in CNC setups but that can only be described as super low speeds - in single or tens of RPMs even. If you're definitely looking for a 2000 RPM on the business end of your application, then it's most likely going to be a three-phase BLDC.

Thanks so much. I am going to try to digest this stuff over the weekend. I might have more later.


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