Re: hot servo motors, heatsinks??

You don't need a heatsink, you need reduction gearing between the
motor and whatever it's running right now.

Servomotors should never get hot. If they do, you are seriously
abusing (miss-applying) them.

A 3:1 reduction will lower the torque-load on the motor 3-fold and
motor 9-fold reduction in heat. You probably have more than enough
motor RPM to make up the difference. The motor will then be cold
while delivering more power to the load.

While I'm on the subject, servomotors are not step motors and cannot
be used the same way. Steppers are high-torque, low-RPM motors.
Servos are low-torque, high-RPM motors. Kind of like diesel engines
and turbocharged Formula-1 engines; the former having perhaps a 1,200
RPM red line while the latter has a 10,000 RPM one even though the HP
may be the same.

That is the reason why you can direct drive a load with a stepper
(1:1 reduction) while a servo has to have reduction gearing (toothed
pulley and belt). Power is speed (RPM) times torque. When you say the
motor is turning slowly, that means it is not matched to the load and
not delivering power to it. Instead it is burning itself up in the
process.

Mariss


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "etauch" <erictauch@a...>
wrote:

> Greetings,
>
> I am currently at the point where I am testing my CNC
> conversion. I notice that the servos get quite hot
> after about 5 min of running. Not so hot that I cant touch
> them, but if you grab one, you can only hold on comfortably
> for a few seconds.
>
> I know they are running at low RPM, so this is probably one
> of the causes (higher I^2R at low rpm?). Also, I am dumping
> many amps into a relatively small mass, so heat is to be
> expected.
>
> My question for those with experience with CNC servo motors.
> Does anyone install heatsinks on them?? At what point should
> you shut down to let them cool off? I think they are ok
> after 5 min, but if I were chugging away on something for 30 min
> or so, I think they might burn up.
>
> Some info on my setup...
> This is a HF 47158 micromill with 190 oz/in servos
> using direct drive (bracket and shaft couplers). I am
> running a Camtronics/Gecko320 servo driver box, and also
> installed a 20lb gas spring to offset the head weight on
> the Z screw.