"Ned Simmons" wrote in message
...
On Tue, 15 Jul 2008 11:53:47 -0700, "Bob La Londe"
wrote:



Would motor efficiency (and speed control) be improved by keeping it
cooler?

I would assume so. The armature winding resistance will rise with
temperature, which will increase I^2R losses. If the speed control
utilizes the usual IR compensation, then the RPM setpoint will drift
as the motor gets hot. But I don't think either was a concern here.

I've experienced this firsthand. I built a device that tested the
leader to hub attachment of video cassettes as they were assembled. A
pair of DC motors engaged the hubs and applied a torque that was
controlled by limiting motor current. The torque would drift as the
motors warmed, not enough to be a problem, but measurable.

That's basically the type of thing I was thinking.