Re: [CAD_CAM_EDM_DRO] Re: Question for Kim Lux

I don't think that 40V and 4 Ohms is realistic for this motor unless
it's huge. That would be 400W in heat. Also if 10A was the max
possible current than this would be stall torque and not rated torque.
Torque would decrease as soon as the motor started turning with a 40V
max input.

Operating the motors at voltages over the specified voltage is OK as
long as it holds together mechanically. However you will have to derate
the 10A continuous if you intend to run the 2500RPM for a long period of
time with significant load. It will not handle 2500RPM and 10A if the
1800RPM limit was related to heat rather than mechanical issues. If you
look inside the motor and the windings are tied and wedged then
mechanically it should be sound. It's hard to say exactly why the
manufacturer marks a specific RPM value. If you are doing it simply to
speed up your rapids(where the current will be pretty low) heat
shouldn't be an issue. Brush bounce can be an issue, this is one cause
of arcing.

I fly electric model airplanes and running motors above the rated
voltage isn't an issue except for brush and comm wear. In that
application cheap motors are expected to be scrap in a few hours of
operation so it doesn't matter. When using high quality motors they can
handle the abuse and brushless motors don't mind much at all as long as
you keep them cool enough. In models the thermal mass absorbs most of
the heat, convection and radiation doesn't come into play unless you
have very large batteries. However in the shop if you want to push a
motor adding a fan will let you get a bit more out of the motor. You
then have to worry about the reliability of the fans.

Yes, by the book you may want to change the ratio to get more speed, but
at what cost? In this case adding a gearbox would add complexity, cost,
increase drivetrain losses,...etc.

The above applies to DC permanent magnet motors.

Greg


Kim Lux wrote:

> I'd like to "over voltage" the motors so that they can run at a higher
> speed. These motors have significant armature resistance and with a 40V
> power supply we run out of supply voltage long before we are anywhere
> near the peak current of the motors.
>
> The max voltage spec on these motors and servo motors in general is
> pretty soft. More important that max voltage is not exceeding a
> practical speed limit, not exceeding max current, etc.
>
> Kim
>
>
> On Tue, 2003-12-23 at 17:31, industrialhobbies wrote:
>
>>Color me ignorant. But why would you over-volt your servos so much?
>>I run and sell Pittman's which are 24v motors, I can do 180 IPM
>>rapids and all that other stuff. So what will you gain? Up to a few
>>volts over isn't all the extra power just going to heat? Which
>>servos don't like.
>>
>>Not that I'm attacking your position. If it works for you I wish you
>>all the best.
>>
>>I'm just curious as of why?
>>
>>Thanks
>>Aaron Moss
>>www.IndustrialHobbies.com
>>
>>
>>
>>
>>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
>>
>>>We are running the them with 40 volt supplies, Gecko 320s and US
>>
>>Digital
>>
>>>encoders, 500 CPR. With a 5 TPI ballscrew, this combo gives
>>
>>1/10,000"
>>
>>>resolution and 150 IPM using TCNC.
>>>
>>>If I had to do it over, I'd use 60 or 80V supplies. It sounds like
>>
>>the
>>
>>>new version of TCNC is going to have a much higher stepping rate and
>>>will allow 250 IPM with this sort of set up.
>>>
>>>Kim
>>>
>