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4 motors on one axis

Posted by rodrigo 
4 motors on one axis
October 11, 2017 05:06AM

I want to know if it is possible to attach 4 motors to one ramps slot and if so, how? I have a ramps premium and nema17s at 1.68 amps/phase. I also have drv drivers and some TB6560 (3A at 24V) if necessary.
The reason why is I am designing a massive 3d printer for a research group and would need 4 of them to drive one axis.
Re: 4 motors on one axis
October 11, 2017 04:18PM
I suggest you use a larger stepper, say NEMA #23 (or a pair in tandem drives), and external stepper drivers for each stepper.

Otherwise, make up a drive board with four (4) TB6560 stepper drivers, and drive one stepper with each driver. They can share the step/direction signals.
Re: 4 motors on one axis
October 11, 2017 06:11PM
If you use 4 motors drive a single axis, they will sometimes get out of sync when you power the machine off and on again. This happens quite often on printers with two Z drivers motors, and it will happen more often with 4 motors driving a single axis.

There are a few ways round this:

1. Don't use multiple motors to drive the axis. Use one motor and belts.

2. Lock the motors together using belts. But one motor and belts is simpler.

3. If the axis is the Z axis, a few firmwares offer a function to probe the bed and adjust the motors individually to level it. You need use a separate driver for each motor to do this.

I am biased (see my signature), but I question why you are proposing to use budget electronics for what will evidently not be a budget printer.

Edited 1 time(s). Last edit at 10/12/2017 02:32AM by dc42.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: 4 motors on one axis
October 12, 2017 02:26AM
Thanks for the fast replies.
I actually do have some nema 23s available but i would like to first exhaust other options with the 17s. I currently have a setup where each motor drives both the top and bottom section of each of the 2 vertical rods which move the y axis however, i had some movement issues yesterday morning with lagging.
After untightening some v wheels and increasing the current they move better now but prob not as fast as necessary (havent tested at higher speeds yet).
The reason to reduce costs is that this is in a way a thesis project to see how cheap can 3D printers be built even at large sizes (print area for this one is one cubic meter).

Tegarding the drivers, does this mean i can drive more motors if i simply plug in more drivers?
Or how do they manage multi-extruder printers?

Edited 1 time(s). Last edit at 10/12/2017 02:27AM by rodrigo.
Re: 4 motors on one axis
October 12, 2017 02:58AM
IMO trying to build a large printer on a budget is a waste of time. The larger the printer, the more difficult it is to get the bed flat and the gantry rigid enough not to sag. Bed compensation only gets you so far.

But if you really want to go this route, you can connect 2 motors in series to a single driver. The maximum speed may suffer, but you can get the speed back by using 24V power, if your RAMPS board is 24V-capable (check the voltage rating of the capacitors) and you power the Arduino by alternate means. So you could drive 4 motors using 2 drivers.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: 4 motors on one axis
October 12, 2017 03:41AM
Well of course it is not really budget friendly, we just want to minimize unnecessary costs by optimizing the design.
I do have 24V taurino and ramps premium.
Re: 4 motors on one axis
October 13, 2017 06:02AM
hi rodrigo,

as dc42 explained you get loss of synchronisation. i used 4 steppers, 2 in series times 2 in parallel - look up the mendel90 wiring diagram. exactly as dc42 explained: it regularly and consistently went out of synchronisation and the printbed required constant and monotonously-regular retuning. the reason is very simple: microstepping interferes with the "sync" on startup. basically you use the difference between two phases to "hold" the motor in a position, between two electro-magnets, where it would not normally be happy to sit. when you switch off the current (power down) and then power back up, ONE of the motors will have dropped clockwise, the other will have shifted ANTI-clockwise when the EM field is brought back online.

now, normally, you sync the motors by doing an endstop "reset", nooo problem, right? endstops go "click" or whatever, and you're synchronised, right?

.... except... because you're driving FOUR steppers from the same Step/Dir you can ONLY SYNCHRONISE TO ONE OF THEM. the other three are pretty much guaranteed to not be in sync, and can NEVER be gotten back into sync.

so when - not if - they get out of sync, you will be forced to power-down, MANUALLY rotate the motors, then power back on again.... and do it again, with a MANUAL check each and every time - pausing the printing to make sure they're in sync.

... do you REALLY want to force such a ridiculous and laborious manual process on to people??

i'm assuming the answer is "no" to that... and that's why people have been recommending that you use four separately-controlled steppers (with an endstop in each corner, preferably, or use a Z-probe and e.g. RepRapFirmware to check the Z-height in each corner).

or, better, listen to the advice that dc42 gave you and use a manual (geared, belt) drive system. that way, you can do a setup / tuning config once and only once, and you can use a single z-switch, and be absolutely confident that when the z-switch hits "zero" in one corner, all other four corners are guaranteed to also be zero.

make sense now?
Re: 4 motors on one axis
October 16, 2017 12:23PM
Thanks Ikcl, desynchronization is a total no-no considering how this printer will probably have 3 day prints on a frequent basis due to the size.
Like I said, I already have a belt-motion system in place but with such a long z-distance, I need to prepare for some lagging on the opposite end of the motors.

If after testing with the current belt setup it still does not work, would you advise then to plug 2 motors on one driver slot and and 2 more on another slot (say one of the extruder motor slots)?

I always thought it was hard to have 4 motors just never guessed synchronization would be the cause...
Re: 4 motors on one axis
October 16, 2017 02:21PM
De-synchronisation is a problem that occurs when you power down and up again. It's not likely to happen during a print, unless you have something mechanically wrong that causes one of the leadscrews to get stuck. So it doesn't matter whether you are doing a 3-day print or a 10-minute one, unless you want your printer to be able to resume the print after a power failure.

However, as a 4-screw printer is nearly 3 times more likely to de-synchronise than a 2-screw printer, I suggest you either make provision for automatic re-sync (which means you need a separate driver for each Z motor, a Z probe, and firmware that supports this resync), or use a single motor and belt drive instead.

Using 4 leadscrews implies that the bed is flexible enough to twist slightly. If the bed is rigid, you should use 3 leadscrews instead, because 3 points define a plane and adding a 4th will over-constrain the bed.

Edited 1 time(s). Last edit at 10/16/2017 05:54PM by dc42.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: 4 motors on one axis
December 11, 2017 03:17PM
I am also building a printer with 4 steppers in the Z-axis for the bed, but I have designed a daughter board, that takes the Z-axis commands and feeds it to all 4 motors but the board has one additional feature, I have a control circuit which tells which motor sees the step and dir signals, I’ve designed it to use one of the servo headers connection to send the “listen” command on telling the board to drive motor’s 1, 2, 3 or 4, or all of them.

But alas I cannot test it as I don’t know how to alter marlin accordingly, and would be extremely happy if someone could help me in this aspect.

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