Look at the RC plane, heli and even car sites they all use brushless motors.

How much power do you want? Look at http://www.mtroniks.net. Not all their motors are large, if you have seen the gas turbine electric loco being built and shown at some exhibs you can see quite a difference.

Martin

I have been playing around with brushless motors designed for the RC market, albeit at the low power end of the spectrum. These motors seem to be able to absorb high levels of power for their diminutive size and have quoted efficiencies of above 70%. Typically a motor of 28mm dia with a length of 35mm can absorb over 100 watts. Sounds good but the downside is the shaft speed which is quoted as KV or rpm/volts and with figures in the range of 1000 to 4000 KV then even at relatively low volts, say 15 to 30, the shaft speed can be well in excess of 15,000rpm .

They also come as out-runners and in-runners. With the out-runners most of the case revolves and is attached to the shaft with the mounting for the motor being on the remaining non-rotating part, often just the front face. In-runners are more like conventional brushed DC motors with the only exposed rotating part being the shaft.

The controllers are designed to be driven from a RC receiver, much like any model servo, and require a pulse width modulated signal of about 5V amplitude with a range of between 1ms to 2ms with a repetition rate of somewhere between 10 to 20ms. This can be derived easily using something like a LM555 timer IC and will drive the motor controller directly, some of the controllers have a BEC function, battery eliminator circuit, which can be used to power the timing circuits.

Some of the larger motors can absorb over 2kW of power but because all of these motors are intended to run on fairly low voltages the current required is very high. All this come at a cost, even going direct Chinese suppliers on Ebay, and of course the shaft speed tends to be fairly high, though the KV figures are lower. Some controllers and motors come with water cooling facilities built in to help with heat dissipation!!. The larger motors often have shaft diameters in excess of 5mm.

The brushless motors used on the mini lathes etc tend, I believe, to work on much higher voltages, probably directly rectified mains, and therefore can produce the power at much lower currents and hence need less robust electronic controllers. Also being designed for static use where size is not the prime concern, unlike in a model, the motors can be much bigger and the increase in rotor diameter will give them higher levels of torque which means they can be run at lower speeds while still achieving the desired shaft power.

Hope the above helps a bit but as I said I am only just beginning to get involved with this technology.

Regards

T'other Martin

PS

Out of interest here is one that is high power and totally sealed

Edited By Martin W on 27/05/2012 11:57:10

Yes, they are available with a wide range of speed ratings. The speed rating is quoted as kV which confused me for a while as that is the abbreviation for kilovolts, however for these motors it is the number of rpm per volt so for 3000 rpm maximum and running off a 12 V supply you need 250 kV.

They will work OK on 12 V so you could use a 12 V car battery connected to a charger.

Russell.

Martin,

PM sent

Ive hear about this chap before but wonder it he reads this forum and would like to post a few words on the subject? Certainly sounds interesting!

Peter

The chap I referred to above gave a lecture at MEX last year on behalf of SMEE – see

**LINK**

and scroll down to find the summary. You don't run them (alternators) as stepper motors but as polyphase motors where the stator phases are switched from rotation of the motor. Speed increases until the back emf equals the volts applied to the rotor, just like for example the outrunner motors used in R/C modelling. That's for a given rotor current – if you increase the rotor current then the motor runs slower but generates more torque.