Re: [CAD_CAM_EDM_DRO] Re: Opinions on these Reliance 0690 servo motors for BP conversion

When I bought these motors I did the same sums and came up with pretty
similar answers. The big problem is that the 2.5HP is intermittent duty
with forced air cooling. The continuous rated torque without forced air
cooling is far less than 23 in-lb.

I initially tried my Z axis 1:1 and the motor obviously struggled.
Rapids were about 100IPM and the motor got hot quickly. Changing to 2:1
improved things a lot, rapids went up to about 180IPM and acceleration
increased as well. Changing to 3:1 would have been better but it is not
easy to do due to the available belt sizes. If I set the Z axis to
continuously rapid up and down the motor is too hot to touch after about
10 minutes.

I did all my testing on the Z axis because it has a huge ballscrew and
the quill is a very close sliding fit in the housing. The whole lot is
bathed in way lube so there is lots of viscous friction. With no belt it
will fall very slowly under it's own weight. However if you try to move
it fast you need lots of power.

In use my motors seldom get above lukewarm. However most of my machining
is on fairly small stuff and I rarely use an end mill bigger than 10mm.

Motor smoothness is also an issue. The motor's torque ripple does cause
a very slight variation when running at low speed. At certain speeds, if
you watch the pulley very closely you can see it speed up and slow down
very slightly as it turns. With Rutex drives you can tune this out
better than with Gecko drives. The best way to reduce the problem is to
increase the encoder resolution. The higher the encoder resolution, the
faster the drive will react to torque ripple. My 200 line encoders are
on the very bottom edge of what is useable. 500 or 1000 line would make
a big difference.

Les

cnc_4_me wrote:

>
>Hi Les, I am glad you posted this reply because I have been wondering
>about your recommendation of 3 to 1 for awhile now.
>
>Is it because you feel you need the extra torque? Or does it have
>something to do with the motor rated at 6750 RPM and it just does not
>run smoothly at low speeds?
>
>Here are the specs of the treadmill motor you use #10-1783 from
>surplus center.
>
>2.5HP at 6750 RPM
>
>Torque in oz-in = (HP / RPM) x 1 million.
>
>(2.5HP / 6750RPM) x 1M = 370 oz-in.
>
>370 oz-in / 16 = 23 in-lb from motor.
>
>At 2.5 to 1 ratio = 57.5 in-lb at lead screw.
>
>At 3 to1 ratio = 69 in-lb at lead screw.
>
>
>
>Wally
>
>
>
>