hybrid steppers

Hi,
I'm about to strart a conversion of a emvio 25 CNC mill (G0704 size) and a bit confused on steppers .
I've read lots of info on steppers and there has been a lot of development of the technology in recent years which has led to some confusion. What i've been pondering on using are a nema 23 3Nm, 3 phase hybrid closed loop steeper (with encoder) with suitable controller. I was intending on direct drive and not use pulleys. Would i need a bigger than 4Nm on the Z as i'm intending on putting a bigger motor and doing a power drawbar or would a gas strut/counter weight be enough.
I can't seem to find any suppliers of 3 phase steppers in the UK of the size i'm looking for unless my googling skills have let me down :hopelessness:
looking at the tormach white papers on why they use steppers and advantages/disadvantages of 2/3 phase and analogue/digital drivers over servo's has left me a bit confused on what would make a nice reliable conversion that doesn't lose steps and becomes a pain which i think only happens if i'm over driving if i understand it correctly.
I did look at the teknic hybrid steppers but postage and import taxes makes them quite expensive are there options i'm missing? or am i doing the normal thing and over thinking and 2 phase hybrid stepper from cnc4you or somewhere would make a nice conversion and should just on with it and stop googling further. I don't think the size of the machine really justifies servo's unless someone doesn't agree?

Regards
Rob

You can now buy clones of the Leadshine closed loop stepper ("Integrated Easy Servo") - the ones with the stepper drive and encoder all integrated together on the motor. I've only used the genuine Leadshine parts but if these clones are any good, they would be a pretty good option for the money.

This Hybrid stepper is driven at 36VDc and we all know it must be driven at 70VDC and 4.5A , so-I dont think so.

I dont see a benefit in a hybrid stepper anyway. Prefer servo motor or a plain stepper.

is there any gearing intended in the CNc kit? if it was me I would prefer my mini CNC mill geared, so be able to do really precise stuff. So no direct drive.


This seems a very good machine, dont be too savy, do it properly and it will serve you right for life.

Hi Rob,

didn't take you long :D

You are aware of my kits are in development right? They are made to accept Nema 23 motors with a 2:1 gearing ratio for the exact reason Boyan says.

4Nm would be more than sufficient and to keep the costs down, I would also recommend going with plain steppers. Did use leadshine steppers on my KRV converstion and the cost/benefit was questionable really.

Best spend money on good ballscrews in my opinion.

R's

Quote:

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Originally Posted by Boyan Silyavski

This Hybrid stepper is driven at 36VDc and we all know it must be driven at 70VDC and 4.5A , so-I dont think so.

I dont see a benefit in a hybrid stepper anyway. Prefer servo motor or a plain stepper.

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Sorry I bothered to offer an opinion. Seems you have an expert here who knows all the answers!

It didn't know that "it must be driven at 70VDC and 4.5A" - that must be a universal truth I wasn't aware of. Sounds as if it will be a hell of a beast. Motors as big as the machine itself.

About gearing down steppers - the torque falls off very rapidly with increasing speed, so gearing the motors down 2:1 probably doesn't actually improve the torque to speak of, yet you will half the maximum speed. Hmm, that's actually made things worse. If you plot the power against speed, you will see that steppers are generally close to constant power, so gearing them doesn't help a lot. It's different for servos which have lower torque but a much better constant torque range, so benefit from gearing down.

If you are looking for good resolution, go for a driver that can achieve proper microsteps (but not too many of them). Or possibly a motor / driver that has an encoder so that it does what you are asking. Oh, wait a minute....

With a 2.5mm leadscrew and 200 steps (no microsteps), you'd get about 12um per step. With only a few microsteps you will be well past what a machine of this build can achieve. You'll be doing extremely well to get under 5um surely?

Quote:

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Originally Posted by Muzzer

About gearing down steppers -

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Acceleration and deceleration 'n' stuff ;-)

Quote:

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Originally Posted by Muzzer

About gearing down steppers - the torque falls off very rapidly with increasing speed, so gearing the motors down 2:1 probably doesn't actually improve the torque to speak of, yet you will half the maximum speed. Hmm, that's actually made things worse. If you plot the power against speed, you will see that steppers are generally close to constant power, so gearing them doesn't help a lot. It's different for servos which have lower torque but a much better constant torque range, so benefit from gearing down.

If you are looking for good resolution, go for a driver that can achieve proper microsteps (but not too many of them). Or possibly a motor / driver that has an encoder so that it does what you are asking. Oh, wait a minute....

With a 2.5mm leadscrew and 200 steps (no microsteps), you'd get about 12um per step. With only a few microsteps you will be well past what a machine of this build can achieve. You'll be doing extremely well to get under 5um surely?

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All very true. more speed less torque. The torque however is more important at the low speeds for acceleration and deacceleration purposes. When you are steady state, you should be ok if you do not want to be running at high rapid speeds.

2.5mm leadscrews would be a waste of time imo. A CNC conversion would need to be run on ballscrews and those are easy to find in 5mm pitch.

You can of course still gear it 1:1 through a belt to retain the handles. I know I used them shitloads on my kneemill conversion.

It all comes down to personal preference.

The voltage you run your motors on will largely depend on your drivers too. I think my original set of drivers from cnc4you disliked being run at 70V so had to get a 48V supply.

Quote:

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Originally Posted by Muzzer

Sorry I bothered to offer an opinion. Seems you have an expert here who knows all the answers!

It didn't know that "it must be driven at 70VDC and 4.5A" - that must be a universal truth I wasn't aware of. Sounds as if it will be a hell of a beast. Motors as big as the machine itself.

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Now you know.

Thanks all for the advice it's helped a lot in my research.
Hi George, it was always the intention to convert as the first project been fun machining the mounts for the CNC conversion on it. Yes i was aware of you plans for the kit but quite enjoying the process of the conversion.

Think i've come to the thinking of nema23 3Nm steppers on the x-y and Nema 34 4Nm on the Z, C5 1605 ballscrews on all axis with double ballnut i'll direct drive to start of with to to see how it goes may change to being belt driven in future from Zapp. Leadshine 808 or 828 stepper drivers. Intention is to run LinuxCNC.
Does that sound like a sensible approach?
Thanks in advance
Rob