Re: [CAD_CAM_EDM_DRO] Re: Declining motor torque with lower voltage.

cnc_4_me wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lance Hopper"
><snaggletto@c...> wrote:
>
>
>>Hey,
>> Mr. Elson knows his stuff, listen to him. However, I would like
>>to add, peak torque values mean almost squat. Your 600 oz-in peak
>>motor probably puts out around 150 oz-in "continuous" torque. This
>>is the magic number. Furthermore, don't ask your motors run up
>>to "max RPM" either. Use around 75-80% of max RPM in your rapid
>>calculations. Good luck.
>>\
>>
>>
>
>
>I have seen Mariss say this too "Use around 75-80% of max RPM in your
>rapid calculations" What is the purpose of this....
>
>

You need to leave a margin for acceleration and load fluctuations. If
the DC power
supply is 70 V, and that voltage will spin the motor at no load at 3000
RPM, you
can't reach 3000 RPM with a load applied. So, you need a margin so the
required
speed can be reached when the motor IS under a load. With a high
armature resistance,
this margin may need to be even bigger.

Another possible reason for this is to stay within the safe operating
area of the motor.
Most motors are rated such that you can have some particular torque up
to some RPM,
but then need to reduce torque load a bit above some speed. The
internal losses in
the motor are a product of speed and torque. If you are running right
up to the very
edge of the safe operating area, you have to trade off speed and
torque. Most of
us don't want to get too close to the boundaries of the SOA, or the
magic smoke comes
out.

Jon