Newbie- Newbie- Servo motor torque question

[byrdman73]

I have a 1996 Lagunamatic CNC knee mill with the old Dynapath controls removed. I've narrowed in on the Logitrol retrofit system with 900oz.in servo motors.

My old servo motors are 40 lb.in (640 in.oz if my conversion is right) and run a 1:1 belt drive. The supplier says that the new servos would need to run a 4:1 reduction. If the new servo motors are 900 oz.in, I should be able to run the same 1:1 belt drive with ease.

Am I overlooking something or is the supplier on crack?

[Bubba]

byrdman
First off, I am no expert. Now having said that, I would have to as about the ratings that you have espoused.
In the case of the original servo, is that continuous rating or max? Same question in the replacement ones. Also, what are the rpm ratings of each of these units?

I would suspect the originals are rated at continuous and the new ones at max (Thou shalt not exceed rating)!

For instance, I have in my box of "stuff" servos with rated speeds of say 1000 rpm to some with 6000 rpm ratings.

So before saying the supplier is on crack, make sure your comparing apples to apples and don't have a rotten banana in there:})

[byrdman73]

Thanks Bubba,

40 lb.in (640 oz.in) is the "torque stall" and the max rpm is 2500. The new servos are "NEMA 34 / 900oz.in Peak Servo Motors with 250 line encoders".

I'll ask the vendor for more specifics on the new servos. I'll update when I hear back.

[byrdman73]

Old baldor servos- (40in.lb) 640in.oz constant stall - 2960in.oz max @2500RPM

New servos- 170in.oz constant stall - 900in.oz max @ 4200RPM

The old motors showed the stall torque whereas the new motor showed max torque. The marketing guys are crafty

640/170=3.76 which translates to a 4:1 belt drive

4200/4= 1050RPM Thats considerably less than the 2500RPM of the old motor, but there has to be some sacrifice for the low cost.

.187 inches traverse per revolution @ 1050 rpm = 196 inches per min

Thats faster than I could crank it with my hand, so I'm OK with that. Further, the accuracy of the 250 line encoder is quadrupled.

I'd like to thanks myself for doing such a fantastic job of explaining this. I love this forum LOL

[kevin swan]

that is what i thought when i read this thread. Can you use your motors and just get new drives ? good luck with this