Two stepper motors for one axis.

[hand1]

When you build a moving ganrty machine utilizing a rack and pinion drive, how do you wire the two stepper motors that drive the x axis or do you have to us an additional driver?

[DIYaholic]

hand1,
Each motor is wired to it's own drive. One motor would be the X-Axis and the other would be the A-Axis and be "slaved" to the X-Axis in Mach3.

Randy,

[lgalla]

Randy,does one motor have to rotate clockwise.the other counter clockwise?

[hand1]

DIYaholic,
Thanks for the help.

Chris

[cheetahcnc]

I run a moving gantry, 61" x 100", rack and pinion drive X and Y, router with two large, 5 amp stepper motors on a 10 amp drive. When I checked with the drive manufacturer's tech, he informed me this was OK. It has run for years perfectly fine like this, and can rapid traverse at 1200 IPM. One issue I discovered was the gantry cross beam was not machined perfectly square, which caused the two motors to have to fight the gantry "square". Once shimmed, it ran much better, and skipped fewer steps. The two motors run opposite directions of each other.

Jim

[DIYaholic]

Originally Posted by lgalla Randy,does one motor have to rotate clockwise.the other counter clockwise?

Good question. I have not built a machine yet, just passing on what little I have learned here in the Zone". I suppose, it actually depends upon how you set up your machine (many non-standard setups have been done), but cheetahcnc posted that they do run opposite directions. I don't know how Mach3 deals with "slaving" motors. Perhaps someone wiser than me can chime in.

Randy,

[lgalla]

RANDY come to think about it,would you reverse the wireing on one motor or would Mach take care of the slave?
Larry

[DIYaholic]

lgalla,

I'll let "The Great CarveOne" answer that:
http://www.cnczone.com/forums/diy-cn..._question.html. I didn't read all of it but the question is answered.

Randy,

[mike_Kilroy]

as cheeta said, yes, you can run multiple steppers on one drive. if both go same dir, then just wire them in parallel to the drive output. If opposite directions as Igalla said to to look for, then one must be wired to go opposite direction.

[avayan]

If the drives are regulating current I would imagine you would want a drive per motor. Otherwise, one motor may not get the current it requires. You would need two perfectly matched stepper motors if you want to ensure they will both take the same current and generate proper magnetic fields. It is hard to believe you will ever get that. At the same time, however, it is hard to believe differences will be so large that the motors will behave abnormally. Somebody mentioned that's how they are doing it, so in some cases it clearly works!

On the other hand, I don't think you need the A axis to drive the second stepper. You can have the output of the X axis to drive both stepper drivers. They will both react at the same time as STEP impulses are registered. If you ever need to re-synchronize both steppers (say one of them lost steps whereas the other didn't) you may need to connect the stepper drivers to different axis outputs, clear up the error in travel, and then reconnect to the existing setup again. So if you are not using the A Axis at all, then it may be prudent to separate the two motors on a per axis basis as stated before.

[mike_Kilroy]

Originally Posted by avayan If the drives are regulating current I would imagine you would want a drive per motor. Otherwise, one motor may not get the current it requires. You would need two perfectly matched stepper motors if you want to ensure they will both take the same current and generate proper magnetic fields. It is hard to believe you will ever get that.

I had assume both motors were same part number when you said u wanted to run 2 from 1 drive. Obviously if they are not the same part no then you dont want to run 2 in parallel on 1 drive. If same part no then you too can run mutliple on 1 drive as many others have and do today. Of course if one looses steps they and they need to be in synch you are in trouble. Of course you cannot gaurantee exactly same current into both so one may burn up. But if the idea is to be really cheap and do this you can do it same as many others do today. If you need to be sure no missed steps, if you need to be sure to not overheat one, etc., then you can buy a couple servo motors and drives and do it right with none of these questions, but is will cost you more. Trade offs one and all.

[avayan]

I may be being a purist here, but what I meant about two steppers with a single drive not being matched would still apply if the motors are of same part number. Agreed you may never see the problems. But my point is that as you regulate current, the H Bridge will ITrip once it reaches the current peak the H Bridge has been set to.

Both stepper motors will be different, I can assure you of that. There are some tolerances we can not ignore and to expect the windings to be identical from motor to motor is ill fated. What I expect to see is that when the ITrip takes place, one stepper winding will have more current than the other stepper winding in parallel. Hence, the magnetic field will be stronger in one motor than on the other.

Like I said, you may never see the problem. But what may happen (BIG "MAY" here) is that at some point in time one stepper will start loosing steps because its magnetic field was just not strong enough. I would expect this phenomenon to get exacerbated if you are employing any form of microstepping with higher resolutions making it worst.

The solution could be to increase the current regulation value so that more current goes into the system. Take into consideration that now you will be heating your motors more (current will have to go out as heat, since the motion is still pretty much the same), and your hammering effect at slow speeds will increase as well, making resonance a little bit worst.

BTW, if you are using an LR drive (which I think nobody uses anymore), then you are in good shape. Both steppers should get the current they need provided the resistor is sized accordingly.

So to recap, it will most likely work, but it may not work ;-) And because this is a CNC machine where you are striving for perfection, such a "cheap" method may end up being very EXPENSIVE!