Re: [CAD_CAM_EDM_DRO] CNC Servo motor gear ratio: overheating. EMC step rate. Tablespeed

Tim Goldstein wrote:

>Jon,
>
>We discussed these particular motors previously on this group. The
>consensus was that these motors were not a good selection for direct
>drive on most mills. The only specs that are on the Camtronics website
>are:
>
>These motors have a 5/8 diameter shaft 1.75L. The bodies are 4" diameter
>and 4.5" long. It has a standard 3.250 DBC on the front face. about 50
>oz in per amp torque and RPM is about 900. 36 VDC PM brush ball
>bearing.
>
>So at 25 rpm for his 5 ipm which I am assuming is a speed he plans to
>actually cut something at I think he will be risking getting very hot
>motors and potentially frying them.
>
>

Yes, I think I misunderstood his original post. I thought the 25 Lbs
of linear force to move the table was the total force he needed, but
he doesn't actually say that. he gives no indication whatsoever of what
cutting forces will resist table movement. I think it is safe to say
that these motors COULD handle the 25 Lbs force without trouble,
but if he is cutting metal, that is another story. With a 900 RPM
limit, he is limited on what he can do in the way of reduction,
although 450 RPM on a 5 TPI screw is still 90 IPM, so maybe
a 2:1 reduction would still be acceptable. I also suspect these motors
could be run over 900 RPM (over 36 V) without harm. If these are
the Ametek motors that have flooded the surplus market, the 4 Ohm
(or worse) armature resistance is the bad news on them. That makes
them VERY prone to overheating on any continuous load.
On any servo application where motors are drawing over a couple of
amps, I really hate to see over one Ohm of resistance.

Jon