[ericclinedinst]

So. If someone were to hypothetically be replacing their nema 34 960oz in steppers from cncrp with servos, what should the kw rating be?

[ger21]

Do you have the 2:1, or 3:1 reduction? And what speed are your rapids set to.

And what kind of servos?


At 1000 rpm, you're 960oz steppers have about 200oz of torque.
A 200w AC servo has about 250oz of peak torque, all the way to 3000rpm. If you went with a 10:1 gearbox, you'd have much more power with the 200w servo. If you want to keep the existing belt drive, then you'd probably want a bigger servo.

[Ctbjdm]

Newbie here with a CNCRP machine on order - can you explain why you would do this (steppers -> servos)?

[ericclinedinst]

Link to the servos.

http://dmm-tech.com/Files/ACSMTR-G1-0815A15B.pdf

I'll be keeping the 3.2:1 reduction.

Do you have the 2:1, or 3:1 reduction? And what speed are your rapids set to.

And what kind of servos?


At 1000 rpm, you're 960oz steppers have about 200oz of torque.
A 200w AC servo has about 250oz of peak torque, all the way to 3000rpm. If you went with a 10:1 gearbox, you'd have much more power with the 200w servo. If you want to keep the existing belt drive, then you'd probably want a bigger servo.

[ericclinedinst]

Steppers will eventually burn you. They loose steps. They heat up nicely on long jobs. Inefficient. Noisy. And the list goes on.

I lost a 5 hour 3d carve yesterday because of them. So hi ho.. ho ho.... off to servos I go.

Newbie here with a CNCRP machine on order - can you explain why you would do this (steppers -> servos)?

[ger21]

Steppers will eventually burn you. They loose steps.

Not if the machine is setup properly, or you don't try to go faster than the steppers are capable of.


With 3:1, I'd probably go with the 750 watt. If you could go 6:1 or higher, you'd get the same or better performance from 400 watt..

750w have ~980oz-in peak torque, which would give you about 5x the power at higher rpm.
400w would probably give similar performance to what you have now.

[Al_The_Man]

I use servo's exclusively, the plus for me is the closed loop aspect, as well as current only when demanded.
Al.

[NIC 77]

So. If someone were to hypothetically be replacing their nema 34 960oz in steppers from cncrp with servos, what should the kw rating be?

Read through this thread:

http://www.cnczone.com/forums/diy-cn...ter-build.html

[louieatienza]

Steppers will eventually burn you. They loose steps. They heat up nicely on long jobs. Inefficient. Noisy. And the list goes on.

I lost a 5 hour 3d carve yesterday because of them. So hi ho.. ho ho.... off to servos I go.

At 1000 rpm, you're 960oz steppers have about 200oz of torque.
A 200w AC servo has about 250oz of peak torque, all the way to 3000rpm. If you went with a 10:1 gearbox, you'd have much more power with the 200w servo. If you want to keep the existing belt drive, then you'd probably want a bigger servo.

That 960in-oz stepper at 1000rpm and 200oz-in of torque is producing around 150W of power. The 400W servo will produce 150W of power continuous and about 450W peak at 1126rpm (1768ipm) (and 1.2kW peak at 3000rpm). I have my doubts as to whether the mechanicals can handle the power. Or, you're limiting the speed at which you run the servo, which would probably be a waste of the servo's capability (meaning money.) In other words, the drive ratio as set up (2:1) does not lend itself well for servos. I think an easy-servo or step-servo system would work better (or an expensive direct-drive servo).

I think a better approach would be to simply change the drive ratio to 3:1 or 4:1 first, and see if the problem persists. Remember the pinion acts as a gear increaser or multiplier, so your 2:1 ratio is negated by the 3.1416 pitch circumference, giving you an effective gear ratio of 2/pi or .6366 motor turn per 1". Or in other words, you're getting 2/3 motor torque at the load.

[DAAD]

@ericclinedinst:

Did you replace the steppers with servos?If yes what is your experience?

Br,

David