Re: Spindle Motors

Hello again, this subject (Spindle Motors) is actually going on in
two Yahoo Groups with different responders. It actually confused me
for a while. Well to get to the point - on the DIY CNC Group the
following was posted.

Nicolas Benezan
August 29, 2007

Hi David, I tried it out. Unfortunately, all of that RC motor
controllers seem to use the same algorithm for commutation. They have
a fixed phase relationship between electrical waveform and rotor
position. The phase angle can be adjusted in software but does not
adapt to dynamical load changes. This is good for a constant load
like an aircraft propeller. It is not suitable for a variable load as
you have with a router or mill. Running the motor without load
results in a real bad power factor and a very high idle current
draw. The motor runs even hotter than with load. You have to prepare
for a lot of cooling problems unless you have the skill to program
the controller to adapt to varying loads.

Regards
Bene
--
Benezan Electronics, Stauffenbergstr. 26, D-72108 Rottenburg Baisingen
CNC- und Steuerungstechnik, Elektronikentwicklung

What Nicolas Benezan seems to be saying is that a RC brushless motor
(being basically a fan) produces a certain horsepower at one speed
thus producing a certain CFM flow at that RPM.

It is a Variable Torque device where the torque varies with rpm –
torque varies as the square of the speed. In cases where the
centrifugal blower or pump discharge pressure is allowed to vary, the
loads will require a varying torque. Flow varies linearly with
speed, pressure and torque vary with the square of the flow, while
power varies with the cube of the flow.

Constant Torque Requirement Throughout Speed Range devices are motors
which the output power requirement may vary with rpm, but the torque
does not vary. Horsepower varies linearly with speed, when speed
doubles the power requirement doubles. Conveyors and constant-
displacement pumps require these motors.

Some machines require Constant Horsepower throughout their speed
range. This application is typical of machine tools. Whereas a
machine tool spindle motor needs to produce a constant horse power
over a wide range of RPM. As the machine spindle produces the same
horse power at lower speed the torque output must increase to
maintain a constant horse power.

A good discussion of this in an applied problem can be found in
Practical Machinist – Topic: Monarch 10ee drive system – repair or
replace?,
posted 01-10-2001, by Edson.

Another good discussion can be found in
MMS Online, "Wye/Delta In Perspective", by Kurt
Zierhut, /articles/019904.html