Anyone here know BLDC motors well? Hobby ones particularly?

I want to use a hobby BLDC motor to power a compact high speed spindle to be used for engraving and the like. Mainly because they are so compact for the power and speed. I cannot find, for a price I can justify, a 24,000 to 40,000 RPM spindle that will fit in the space I want to put it. Looking at some hobby BLDC motors and then buying some to experiment with leads me to think that one of these motors may work. I have looked online for answers about these motors and maybe I'm just dense (good possibility) but I haven't been able to find exact answers. Maybe someone here can help. Motors are rated RPM/volt. This means maximum RPM per volt of course. If the motor is supplied with a higher voltage from a supply that limits the current to stay below the specs of the motor will higher RPM be possible? The ESCs (Electronic Speed Controller) are voltage and current rated. Could the output an ESC rated for a lower voltage and current be used to drive control power transistors in order to get around the lower voltage and/or current rating if a sensored motor is being used? I don't need to use a hobby ESC but they are plentiful and cheap. And all assembled. Which is most important. But I would be fine using some other BLDC motor driver in order to get the desired RPM that I want. I can do all the precision machining necessary to make the spindle that will hold the carbide cutting tools and to interface the motor with the spindle. I do not yet know enough about balancing in order to dynamically balance a motor which causes too much vibration from an out of balance condition but I think I can learn enough to do it. I am good with mechanical systems and have a pretty good intuitive feel for them. It's the electronics I'm no so good at. Thanks, Eric

Reply to
etpm
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Yeah, RPM is limited by the back-emf. That is the motor acts like a generator when running and the driver for the motor needs to make a voltage that exceeds the voltage that the motor is generating. The faster the motor is spinning the more voltage is needed.

That depends on how the ESC interacts with the motor to monitor the rotation of the motor.

Probably yes.

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Reply to
Jasen Betts

Remember that at some point (likely to be "experimentally determined", whether or not you intend to) the rotor may mechanically fail when overspeeded. This tends to lead to an abrupt stoppage and the need to sweep the remains into the trash.

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Reply to
Ecnerwal

You have to watch out for shaft whirl, which happens when the rotation rate is close to the first bending resonance of the armature. It'll destroy itself if run near that speed for anything but the briefest of moments.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Yeah, I learned about that years ago when designing and building a stepper motor driven positioning table. I had to watch out for whip in the leadscrew when I changed the drive to a much faster servo motor. Eric

Reply to
etpm

At 40,000 rpm, an electric motor has high frequency AC on its soft iron parts, and a permanent magnet rotor is hard (because magnets aren't easily machinable) to balance.

Have you considered air-powered options? At 25,000 rpm, a dental handpiece is considered 'low-speed'. I'd consider the low-cost option of using those...

Reply to
whit3rd

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