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

I agree that the spec doesn't make sense. These motors have 50 oz-in
per amp torque, 4" bodies and a 5/8" shaft. These are relatively
torquey motors.

Kim

On Sun, 2003-06-08 at 22:10, Jon Elson wrote:
> 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
>
>
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Kim Lux <lux@...>