On Wed, 02 Mar 2011 22:26:21 -0500, Existential Angst wrote:
Just curious about treadmill motors.
Most treadmill motors I've seen are brushed. Is it likely that newer
ones are brushless, and if so, are the electronics that make the motor
brushless internal or external to the motor, and how would I tell?
Normally they're external to the motor, but I've seen purpose-built
brushless motors that have the electronics built in. I wouldn't expect
that here.
The vast majority of brushless motors are three phase, and will have
three (or very slightly possibly four) big wires coming out. Brushless
motors that have to be well controlled all the way down to a stop will
also have additional sensors -- for a treadmill, I'd expect three Hall
sensors, which would mean five to nine little wires coming out of the
motor.
So: two wires means it's brushed, or brushless with internal electronics.
Three heavy wires and five light wires almost certainly means it's
brushless and it has external control. Ditto three heavy wires alone.
Other combinations of wires -- who knows?
I'd
hate to find out a motor is brushless, and that I threw away the goddamm
electronics.....
That would be a pain.
Couldn't treadmills use AC permenant magnet motors? Aren't they a
little simpler than the DC?
There's not a whole lot of difference between an "AC permanent magnet
motor" and a "DC brushless motor". The big difference is that an "AC PM"
motor has a sinusoidal voltage characteristic as it spins, and really
likes to be presented with a sinusoidal voltage on each wire to make it
go. A "brushless DC" motor has a voltage characteristic on each coil
that's more trapezoidal, and you can match the flat tops of the
trapezoids with the DC voltage that's switched in and out.
So while it may be more complicated to _make_ a brushless DC motor, it's
certainly easier to _drive_ one.
It seems that the older DC treadmill motors, altho rated lower in power
than modern treadmill motors, pack a lot more punch to them. No
surprise.
Who'd a thunk? :-).
--
http://www.wescottdesign.com