Re: [CAD_CAM_EDM_DRO] Temperature of a brushed servo motor?

Tim Goldstein wrote:

> Just got the Z axis of Bridgett running with a permanent magnet brushed DC
> servo motor and a Gecko G320. So far about 45 ipm on a -Z rapid (lifting the
> table) without fiddling with the acceleration. A great improvement over the
> stock 12 ipm and healthy increase over the 24 ipm I was getting with the
> original stepper motor on a G210a.
>
> Question is, how hot is it acceptable to run a brushed DC servo motor. I had
> the gain and dampening cranked a little high and the motor got hot to the
> touch on the outer case (I would guess it was 120 - 130 F). I will try it
> tomorrow with more appropriate settings, but I am wondering how hot is it
> normal to run a brushed DC motor. I am guessing that if you keep them at
> room temperature you are not driving them as hard as they are designed.

Gee, was it dithering a lot? My X and y motors run pretty warm due to the
shunt field windings. But, my Z motor runs stone cold under all circumstances.

There just isn't enough Z movement in most of my almost-2D programs to
make it work hard. Most servo motors are only run at their peak rating for
an instant, and rarely reach their continuous rating. Now, in a commercial
CNC machine that is turning out parts all day, and keeps the axes moving
all the time, that is different. But, i have some peck drilling programs that
have
the Z in almost constant motion for over 5 minutes per part, then a minute
to 'cool off' while I change parts. The motor has never gotten detectably
warm on that job.

This is not to say that getting the motor a little warm is a bad thing. The
magnets need to be kept to a reasonable temperature, but probably most
magnets today will handle 100 C without harm. The tricky thing is to
know the temperature of the armature wire buried deep in the windings.
That is real hard to know. If the motor has forced air cooling, it can
probably extract the heat from the armature fairly well. if it is sealed,
the armature could heat up a great deal without the heat transferring
to the housing much. That is a worry, and hard to really know what
is happening deep inside.

Jon