Re: [CAD_CAM_EDM_DRO] Re: Differences between AC & DC brushless

bitnick78 wrote:

>Let's limit our discussion to only 3-ph PM motors.
>
>Here there are still motors called "3-ph AC" and "Brushless DC". But
>what you're saying is that, as long as they have the same type of
>encoders and current and voltage ratings, they are interchangeable
>from the driver's point of view, no matter if it uses trapezoidal or
>sinusoidal commutation?
>
>This is interesting bescause there are quite a few high performance
>used or surplus 3-ph PM motors out there, but very few drivers that a
>hobbyist can afford (The Rutex is the only one that comes to mind).
>So if one could just buy some 3-ph PM motors and hook up to some
>Rutex drivers, this could be an interesting high-performance solution
>for a hobby machine or retrofit. One would just have to make sure the
>commutation feedback were compatible.
>
>

Well, I'm not the world's greatest expert on this. But, I believe that
any brushless PM motor will work with either driver. But, you may not
get full performance if the motor winding is not the type the driver is
expecting. The difference between the two waveform types is not that
great. There may be some motors that really do produce a trapezoidal
waveform when rotated, but I haven't seen one yet. I have seen some that
produced non-sinusoidal waveforms, but they were not truly trapezoidal,
with a flat top.

At low speeds, there might be some velocity or torque fluctuations at
the commutation points, also, if the driver is designed for a different type
motor. I think that's the main reason for the change to sinusoidal drive
is to get rid of the discontinuities at the commutation points.

I suspct the Rutex needs a specific encoder arrangement for commutation,
and uses trapezoidal drive, although they don't specifically say.
You should direct your questions to them about this issue, and
what motor types they have tried it with.

Jon