Anyone here know about BLDC motors?

These motors generally use 3-phase variable-frequency variable-voltage power. If they are for hobby use, then generally there ought to be a recommended driver for the motor. The electric model airplane crown runs these things at insane RPM. So, there must be info on doing that.

I make both brush and brushless motor drives, I don't recommend hacking into one unless you have extensive electronics experience. There are a LOT off issues involved in upgrading one of these.

Jon

How much power do you need? The BLDC motors do not conform to the RPM/Volt way of rating - it is the frequency, not the voltage that controls the speed.

Using a hobby moitor and ESC speed control is pretty simple using either a "servo tester (basically a 555 timer unit) oran arduino

They are not so compact when you factor in cooling. Marine ones (often) use watercooling jackets and they do short bursts at max amps.

The speed goes down as the size goes up. There are differences in windings

- more (thinner) turns means less amps but more rpm.

There are differences in numbers-of-poles and numbers-of-magnets. These affect the necessary programming of the ESC, and its programming-and- design will limit the maximum frequency (~rpm) at which it can drive any motor.

There are inrunner and outrunner types - in and out referring to where the magnets are in relation to the poles. Inrunners tend to have higher speeds for a given power, and are probably simpler to mount and cool for what you want to do.

Motors are limited by heat, not current(directly). If you can keep it cool it does not matter what the rated limit says. The ESC is limited by both heat and voltage - if you can keep the power chips cool you can beat the first. You can't beat the second.

I don't think there's much point to using a "sensored" motor - those are useful for controlling the motor from zero rpm to some small value. They have a fixed sensor and cost more and need a more complex ESC. I think they might also use the sensorless feedback - it's there and they have a computer on the ESC, why not.

The "sensorless" ones just need the ESC to use feedback to decide which way the motor is going. What they do is guess, give the motor a tiny kick and see what happens after that, and if it's wrong they switch direction. I don't know but it seems reasonable it could decide in less than 1 rev, maybe a few degrees.

Sensorless ones means you can't use outboard power transistors because the ESC will be blind. Just get a bigger ESC.

There is likely some combination out there that will work - most motor vendors will give a max amp@volt or watt figure as well as a kV and it does not sound like you need much. 40K is on the high end of what I've seen and they were small. With a good quality motor and ESC and cooling jacket and water-pump and powersupply you may be on the far side of $200.

I've wondered about that "kV" figure too - I may get an optical tach to play with.

Eric - BLDC motors require a controller as a rule, no carbon contacts to the armiture (forgot the proper term). The normal, ie old fashioned, are the voltage/speed versions. A simple control situation. If you use a seperate spindle and motor setup as you state, the motor doesn't require the fancy bearings that the spindle does and A belt drive system has advantages mainly each can be simpler than the combined spindle motor version. For a motor with that setup, take a look at the electric model airplanes. They have remarkably powerful little motors.

Hul

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