Motor speed (was Re: Question for Kim Lux)
Posted by
Greg Jackson
on 2004-01-05 20:11:42 UTC
Years ago I worked with people who designed servo motors. The standard
technique for speed rating of brush style motors was to spin them under a
heavy load using a dyno and watch for arching. While there is a pretty
definite transition between "a few sparks" and "spark crossover", in reality
it was pretty much a judgment call based on experience. It was the brush
arching issue that set the maximum speed on brush motors.
I believe that the maximum speed of brushless motors is more related to
bearings, load, and rotors blowing up. Normally you have to get pretty high
or build a pretty crappy rotor to have a PM rotor blow up on you. In my
experience, most brushless motors are rated in combination with a drive and
the back EMF is the main limitation, setting the envelope of the
speed/torque profile.
I found it particularly amusing to read internal Allen Bradley documentation
that said that the max speed of any AB servo motor was determined by the
marketing department. Yea, like physics is not an issue, it's just the
decision of some pointy hair guy. Very Dilbert, very Allen Bradley.
GTJ
-----Original Message-----
From: Robin Szemeti [mailto:list@...]
Sent: Monday, January 05, 2004 6:26 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Question for Kim Lux
Sure .. I'm just not sure why you think they have that 'max rated RPM'
sticker on them?
technique for speed rating of brush style motors was to spin them under a
heavy load using a dyno and watch for arching. While there is a pretty
definite transition between "a few sparks" and "spark crossover", in reality
it was pretty much a judgment call based on experience. It was the brush
arching issue that set the maximum speed on brush motors.
I believe that the maximum speed of brushless motors is more related to
bearings, load, and rotors blowing up. Normally you have to get pretty high
or build a pretty crappy rotor to have a PM rotor blow up on you. In my
experience, most brushless motors are rated in combination with a drive and
the back EMF is the main limitation, setting the envelope of the
speed/torque profile.
I found it particularly amusing to read internal Allen Bradley documentation
that said that the max speed of any AB servo motor was determined by the
marketing department. Yea, like physics is not an issue, it's just the
decision of some pointy hair guy. Very Dilbert, very Allen Bradley.
GTJ
-----Original Message-----
From: Robin Szemeti [mailto:list@...]
Sent: Monday, January 05, 2004 6:26 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Question for Kim Lux
Sure .. I'm just not sure why you think they have that 'max rated RPM'
sticker on them?