Two stepper motors on one output-port

[Daffy]

On my homemade cnc-machine I have connected two stepper motors on the x-axis. Both steppers are controlled from one output one the controller pcb. Seems to have worked rather well for a long time.

What suprised me was that I one day rotated one stepper by my hand,
and the other one was following, without any power being connected.

Since I work in the electrical-business I know about motors and generators and stuff, but steppers are unfamiliar.

Even when moving rather slowly and only a few degrees, the other one followed.

So my question is: Is it not a good idea hooking two steppers in parallel?
Or can I connect some diodes "somewhere" to prevent the motors running each other?
I don't know if this is a "problem" when they are running by the pc.

I have had incidents where it seems like they don't cooperate. But I have thought it was more like mechanical related problems, but maybe this is a part of the problem..

[beliefdrive]

you need two driver, for two stepper motor, can't conect paraller

[Daffy]

Fast reply
Btw. Here is a picture of my machine:
http://www.cnczone.com/forums/showthread.php?t=93676

My drivercard has 4-axes.
So it is a better choice to use the 4th axis to control the second stepper for my x-axis by mapping the x-axis to both x-axis and a-axis then. (X,Y,Z,A-axis.)
It is really important that the two steppers move simultaneously, or the milling will fail, and in worst case the whole moving assembly will be jammed...

[beliefdrive]

just conect paraller C axis and X asix input ( step and dir)

if it worng direction, you need swap 2 wire of motor ( A+ and A- )

b.r

[pfred2]

Quick, patent your magnetic transmission! I hooked two motors together here to check it out and I think its pretty sharp. Before I read your post I knew about stepper motors being stiff when all the leads were shorted together but I never tried this connect two motors together trick.

If your system works well who can fault it? On the other hand two motor drivers may work even better. I guess there is only one way for you to really find out. With two motor drives you could invert the direction one one too and try out the different configurations that would allow.

[Arquibaldo]

Actually, this is a well known behavior of motors with permanent magnets... I use it
all the time to test (well, at least to have a rough idea of the condition) a pair of identical
steppers when I find them on the scrapyard: just twist the wires in parallel and see if
one follows the other & vice-versa - no tools, meters or drivers needed...

As far as paralleling two identical steppers using a single driver, in principle it should work,
provided, obviously, that the driver has current capability at least equal to twice the current
needed for each stepper...

Nelson

[Daffy]

Yes, I guess it might be well known, I had no plan to announce a new discovery

I was just wondering if this behavior is problematic or not when driving two in parallell.
I have had accidents, where I have managed to snap off a flexible coupling between the stepper and the leadscrew, but I don't 100% know why. It can for sure be a design issue..

[pfred2]

Often when I see dual motors on an axis I see them in opposing corners. I guess people want there to be power at both sides, or have some other even power distribution scheme in mind. Then I'd imagine they use two motor drivers, and invert the direction signal between the drives. Though coil phase transposing can reverse motor spin too I've found.

I could see one motor stalling, missing steps etc. leading to racking on the axis and possibly other difficulties. Such as coupler snapping you make mention of. Maybe there is an invention in your misadventure after all? You could develop the missing step detector to keep your machine synchronized.

Anyhow, I couldn't see myself using more than one motor on a drive. Not to say that there is anything inherently wrong with it, just with my luck I'd end up with problems trying to get away with it.

[Larken]

Thats pretty cool

I tried it with a couple of motors and it works good !

That would be useful for remotely adjusting something like a mirror or camera without any complicated contoller or power needed.

Also maybe a stepper could be used as a MPG with a decoder circuit .... Hmm

[pfred2]

I have a pair hooked up and find myself fooling with them every now and again. It's like magic!

[Daffy]

Originally Posted by pfred2 You could develop the missing step detector to keep your machine synchronized.

Where can I find info about the missing step detector?!

I think I'm gonna try to get each stepper one driver each. It's worth a try.
The whole idea for the design of my machine was drawn from some photos in a forum with a language I could not read

[pfred2]

I don't think you can just hook a missing pulse detector circuit up to your machine and it'd work. In order for the detector to work it'd be more complicated than that. Then at best all it could do is tell you have a problem you already know you have. I don't see how a detector telling you something you already know is going to help you much. Easier to just hook your second motor up to another drive. I think doing that would hopefully be a solution to your whole dilemma. If it doesn't then maybe you'd have to explore more esoteric solutions to your problem like:

http://www.google.com/search?hl=en&q...&aq=f&oq=&aqi=

But lets all just hope it doesn't go that far! Good luck, I feel a second drive will be your cure.