Hi,

I'm Iooking at these Korean servo stepper/drive units:

http://www.fastech.co.kr/English/Ezi-SERVO.html

Particularly the NEMA34 '86' series steppers - specifications below ... They can go up to 32,000P/R res which can be divided down to 500 - They also claim some impressive advantages over standard stepper drive system, or so they have led me to believe - maybe as a beginner I have been bamboozled by jargon ?  

I'd use them firstly in a mill/drill CNC conversion, where they may be over specced (?) - and over priced (?) -  but I will end up using them in other projects also, I'm mainly concerned with what I don't know about the extra costs involved - I imagine a breakout board would be required, which might be cheap enough, but what about 40~70v power supply per axis for 4 axes ?

They'd run open loop with respect to mach3 ? but closed loop internal to themselves ?

Any chestnuts of experience would be greatly appreciated -  Maybe they really are a nice piece of kit ?

Kind Regards,
N

Just had a quick look and really dont see the advantage of this, yes it seems the motor will go back to the correct position if steps are lost but by that time I would imagine it is too late as the job has already gone wrong.
Steppers lose position when they are overloaded so they will only return to the correct position once that overload has been removed and again I think that would be too late.

There may be more to the drives than what I have seen from a quick glance, but what they would have to do is sense the overload, reduce that overload by slowing and then try and continue. That would be fine on a single axis but where 2 or more axis are being moved in sync then it would only be of use if the other axis was also slowed.

Hood
Hood

Thanks for you reply,

Two immediate thoughts:

isn't that the same issue for any servo ?

Interesting point re. the two axes - do people ever use rotary tables to get around using two axes for off axis cuts ?  i.e. rotate piece to X or Y - cut - rotate again - cut - etc... Circles easy also - I guess arc's would have the issue of two axes (X or Y moves with rotary movement) -  I have a rotary table and am keen for four axis 

As for the benefits of the fastech - I was looking at the front page of that link I posted - stuff like this:







and so on...

marketing hoohah or ?

Thanks for you reply,

Two immediate thoughts:

isn't that the same issue for any servo ?

Yes and No, a servo when falling behind will usually have plenty in reserve so the drive can compensate and move the motor to where it should be. If it goes out with the following error set for it so if the drive cant get it to the correct position within the correct time/distance it will fault.
 A stepper when its falling behind is because its overloaded so has no more to give so the drive cant give it more so the only option would be to fault it.

Interesting point re. the two axes - do people ever use rotary tables to get around using two axes for off axis cuts ?  i.e. rotate piece to X or Y - cut - rotate again - cut - etc... Circles easy also - I guess arc's would have the issue of two axes (X or Y moves with rotary movement) -  I have a rotary table and am keen for four axis 

Many people use a rotary axis but not for doing circles, the axis should handle that no problem, if they dont then the motors are not up to it or the mechanics of the machine are too sloppy.

As for the benefits of the fastech - I was looking at the front page of that link I posted - stuff like this:







and so on...

marketing hoohah or ?

I have no idea what they can or cant do or whether its hype or not but what I can say is I dont think in a machining perspective it will be of benefit. A stepper is very accurate unless its overloaded and once overloaded its no use, so correct sized steppers and the problem is not there.

Also worth pointing out there are a lot of differences from one servo system to another so giving a general sweeping picture as above is just good marketing IMO.

Hood

heh, more images from the website:

Do you think the XL motor (blue line) has enough torque for a mill/drill CNC conversion ? (ballscrews will be used) - I'm guessing it does, but how does it compare to a proper servo, especially at the higher RPM ?  It weighs 5Kg by the way   

If I decide to keep its speed range from 0 - 1500 RPM then my minimum torque is around 6 N.m (850 oz.in) - I can 2:1 gear it for double speed and still be 425 oz.inch - and the resolution of steps is still not too jerky once the encoder P/R specs are looked into. Is this logic sound ?



In general I'm finding this whole servo/stepper/drive decision very hard - so many opinions, so many ebay listing telling you their way is the best etc... I figured that buying a driver and motor combo would at least ensure I'm getting the most out of both, no wasted specification either way.

What is an equivalent servo set up ? I understand Gecko have servo drives, but then I'm stuck with the question of what are appropriate motors to go with them ...

The torque will likely be enough for a mill drill.
 A servo will have an almost flat line from zero RPM to its rated RPM for torque, maybe dipping slightly as the RPM reaches the rated speed.
As for servo drives have a look at this page http://www.thecubestudio.com/ServoDriveReview.htm
I have both Steppers and AC Servos on the machines I have and each have their place. For a mill or lathe of a reasonable size I would now not use anything other than an AC Servo but on the coil winder I made a servo would be overkill although the noise of the steppers is a bit annoying at times
I also have steppers on the Bridgeport and although I have no problems with them as far as accuracy and losing steps they are slow, particularly on acceleration compared to the AC Servos I use on the other mill and the lathe.

Word of warning though, often places that sell the servos for hobby use quote their peak output, so you have to take that into account. Much better to find what their rated output is and work with that.

Hood

Here is the torque curve for the motor I use on my lathes Z axis. Most servos whether AC or DC will have a similar shape to the graph.
Hood

Hello Hood,

Those are some powerful motors for CNC if I'm not mistaken !

We use 18 N.m motors at work to move tonnage up and down, counterweighted yes, but running at 2m/s or so she picks up a fair bit of momentum There are large safety factors involved in what I do also

In the meantime I'm learning slowly what I need and come up with a slightly better specification:

************

I have two applications that I'd like to purchase motion control gear for - I'd like to try to get gear that can be used in both applications (there maybe a little adaptation involved in one or more of the cases):

First application:

A 4 axis mill/drill CNC conversion using EMC2 as the controller (the 'loop') or mach3 if that proves troublesome

Second application:

A generic 4 axis machine in which the purchased drives can handle being fed simple step/dir pulses (from an arbitrary source) with the drives doing their own PID control internally (no more PC attached!)

Consequences I've discovered that will likely need addressing:
-I will likely need some sort of USB or parallel I/O card to free me up of on board parallel port restrictions in EMC2 (I'd prefer not PCI bus) - Mesa gear looks interesting here as it is EMC2 ready
-Once the above point is taken care of its looks like I can have high resolution (incremental) encoders - I'd like them for obvious reasons
-The motor drives would be good if they were able to be hijacked or switched to allow the encoders to go to EMC2 directly (or indirectly) for the CNC, the motors would then run 'dumb'. (If this is impossible within the spec I give then I can run EMC2 (or mach3) open loop with the drive running the loop.)
-Assuming the last factor can be addressed I need ALSO to be able to split the encoder stream for the second application, one stream to the drive for its internal PID loop again ('smart' mode), the other split to the arbitrary 'brain' for other purposes (non real time, non control).

Limiting factors:
-I'd prefer brushless servos for the motor, but standard servos are fine also
-COST - I'd like as high torque as I can get (NEMA34 likely?) but don't want to be spending more than around $600~$700 per axis - factor in eventual power supply cost into this also
-I live in single phase 230-240V/50Hz land - thats 10A per circuit ...     2400W max available per circuit

Notes:
I would emphasis the ability to function relatively unhindered or adapted under the second application as more pertinent than the EMC2 CNC application - that can run adapted/converted if need be...
The motors will probably be over spec for the CNC application, excess torque however will be used in the second application.

**************

Any thoughts ?