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two steppers on one axis

Posted by geronimo 
two steppers on one axis
March 02, 2011 08:01PM
Hello everybody, I'm just new to this forum and like to start with a strange question... ;-)

I was thinking if it's possible to connect another stepper driver in parallel to one, already assampled on the RAMPS board.

For my idea of a new reprap design, I need two steppers in the x axis, driving synchronous.
So I planned to solder two pololu stepper drivers on each other for the x axis (of course not solder the pins A1A2B1B2 of the second driver with the first). One stepper motor would be connected to the RAMPS pins and one to the second pololu board directly (pins A1A2B1B2.)

Hope you get my meaning and have some comments on this idea... ;-)

Re: two steppers on one axis
March 02, 2011 10:25PM
I think that's a very standard thing to do. The prusa design has two Z steppers, and IIRC I've seen that advised as the way to connect them.

I'm building it with Baling Wire
Re: two steppers on one axis
March 03, 2011 05:46PM

In regards to your idea for a new reprap design..

I built a mendal design type machine using two stepper motors for the Z axis. I wanted to be able to keep both stepper motors in sync and not have the extruder head crash into the print plate at one end. I ended up using two stepper driver boards, two Z axis sensors with an additional PCB to allow driving the two stepper drivers and sync-ing both motors.

I previously built a dawin machine that used 4 stepper motors for the Z axis and found that sycn-ing was an issue at times. I had 2 stepper motors in parallel from one stepper driver and a second stepper driver driving the other 2 stepper motors (in parallel). Both stepper drivers were wired in parallel for the logic signals (enable/dir/step).

I have a look at below link, it may give you some idea's.
cheers Bruce

Re: two steppers on one axis
March 03, 2011 10:59PM
thanks for your replies smiling smiley

I checked the battle-tank design, a great machine!

But I planned to do it a way simpler, just use common, ready to buy electronic designs, like in my attachments.
Do you think, I still need something like your auto sync pcb? Or did u go this way in order to connect the stepper drivers directly to the processor?

Re: two steppers on one axis
March 05, 2011 10:28PM

You don't have to auto sync the two axis stepper motors. You can just common up the stepper driver inputs (Enable/DIR/Step) and connect them directly to the processor. This will mean that each stepper motor will move in sync from their start position. The issue is, if the stepper motor that doesn't have the home sensor moves for any reason (e.g. being manually turned, vibration when not being used or a possible power off when moving), then without auto syn, this motor will keep in this out of sync position unless it is mechanicialy linked to the other stepper motor .

I used auto sync (when homing) on my two Z axis stepper motors to make sure my extruder never got out of sync and hit my print bed.
I was also pushing the limits of different future design options for Mendels. However I have to say the auto-sync of the Z axis has been great for my machine. I have no worries when going to print that a stepper motor has moved... I can turn either z axis stepper motor and know that they will sync when being homed at startup.

You could try without using an auto-sync feature and see how it works, a number of people are doing this way, Don't know whether they are having any issues. If you have issues then you still have an option.

I can see someone writing some processor firmware that would allow the use of two stepper drivers for one axis that allows the processor to auto sync (Processor will need enough program capacity and enough outputs/input for second stepper driver PCB and home signal) . Then you would only then need a home sensor for each stepper motor ( total of 2 ) without the need of an additional auto-sync PCB.

Cheers Bruce
Re: two steppers on one axis
March 09, 2011 08:35AM
Thanks Bruce,
I'll try your proposals and check whats the best for my design... ;-)
When its finished and working, I'll post it in the wiki...
Re: two steppers on one axis
February 20, 2012 02:24PM
It looks folks like wiring paired steppers up in parallel rather than series.

It seems like if someone was using a current limiting driver like a Pololu, you should wire the motors in series, so that if you open circuited one stepper's coil, the other wouldn't get double the current.
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