Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: moorea21 on August 07, 2010, 05:47:43 PM
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Hi,
I'm wondering what the problems are with wiring 2 steppers into 1 driver, and just doubling the current? I intend using a motor at either end of a long bike chain; the chain will hang very slack, and the 2nd motor is just there to stop one side of the chain clashing into the other.
The application for this is a revolving 'carousel' pen holder for a large plotter.
Only got 1 axis left in Mach, but 2 motors left in the box! It's tempting to try it, but there must be a reason nobody does it that way.
Rich B
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This is generally not recommended - however, I've built several machines driving two steppers from one driver and it's worked very successfully. There are many factors which can make it a bad idea BUT generally speaking - success is inversely proportional to motor speed if that helps.
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Thanks Stirling,
I had thought of splitting the signal from the controller to 2 drivers, each with it's own motor. Probably with a line driver before the split. Would that get round the potential inductance problems? Keeping speeds low would be fine, but so would knowing I'm not killing my drivers...
I may just drive the whole thing through a screw, as the weight is beyond what the motor would like, ie 7kg vertical lift, albeit at low speed. Also the holding torque woyuldn't matter, as the pitch of the screw would hold it. That way I only need to use the one motor.
If it doesn't work, I'll be back!
Rich B
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2 drivers off of 1 signal is a much better solution than 2 motors off of 1 driver.
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Hi,
Mi controller is a Hobby CNC Pro 4axis , 3A max per axis, I want to drive small stepper motors from dot printers , that are 12volts 0.75A each,I need to drive two steppers in one axis for prevent racking and gat more torque. I can't slave motors in X and A axis because I need A axis for other use. Iam thinking if is possible drive this two motor in one axis considerating that current in both motors in less that total current in one axis. I have fear principally to damage chips in controller doing this.
Do you think that this can burn my controller? Or bad results could be only lost steps and other minor problems?
Thanks in advance for your help.
Rene
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There's some stuff on cnczone by Marris and others about this but I can't find it at the moment. I seem to remember though that it went something like this: Stepper motors don't play well together off one driver. If you keep speed down to no more than two revs/sec then it'll probably be ok. Otherwise oscillation will occur and one motor is likely to draw all the current and the other will stall.
Now Marris has no doubt forgotten more about stepper systems than I'll ever know, BUT - as I've said above I've done this on several of my systems and never had a problem and that was with the motors doing up to about 10 revs/sec. Maybe geckos are even better than Marris thinks!
Personally I can't think of any reason why your drivers should be at risk but it's ultimately your choice.
2 drivers off of 1 signal is a much better solution than 2 motors off of 1 driver.
Well as I've tried to say - that depends. Are you for example suggesting that I should buy a fourth driver at over $100 a time for each of my systems that work perfectly well with three?
Cheers
Ian
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I'm wondering what the problems are with wiring 2 steppers into 1 driver, and just doubling the current?
In principle, it electronic terms, it is a BAD idea. You cannot get the motors to share the current properly.
However, if you want to try this, and each motor has 4 phases + common, then up the voltage a little bit and put a power resistor in series with each motor. Not perfect, but tolerable up to a point (determined by experiment!).
If the windings are being driven in push/pull (ie no common), then don't do it. Bad karma.
Cheers
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I can't slave motors in X and A axis because I need A axis for other use.
Why not slave it with another axis (A or B) then?
Hood
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Mi controller has only four axis , and I need A axis for other purposes, Iam trying to use small stepper motor from printers, using two I can prevent racking and get more torque.
2 rev sec is 120 rev min, I will use a 11 mm pulley then at 100 rpm I will get 100 * 11 *3.14 = 3454 mm/min
is faster that I need.
My steppers are unipolar 8 wires,
RCAFFIN please, could you send me a diagram of suggested connections?
Thanks in advance for your help, other advices will be well received.
Regards
Rene
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However, if you want to try this, and each motor has 4 phases + common, then up the voltage a little bit and put a power resistor in series with each motor. Not perfect, but tolerable up to a point (determined by experiment!).
If the windings are being driven in push/pull (ie no common), then don't do it. Bad karma.
There is absolutely no need to do this. And he's said they are 8 wire motors. Just wire the motors how you like - serial bipolar, single coil bipolar or parallel bipolar whichever suits your application and then wire the two motors in parallel to the driver. As long as your combined rated current is what your drive is set to *source* you won't be current *starving* your motors. But BTW - even if the calculated current "draw" of your motors was MORE than your driver can source you won't damage anything - your driver is a chopper drive - it will NOT source more current than it is set to source - but of course you would then be current *starving* your motors.
My steppers are unipolar 8 wires,
No, your motors are not unipolar motors, they are 8 wire motors - there is a difference. They can be *wired* unipolar or of course bi-polar.
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Hi stirling
Sorry my ignorance, and time to response your answer, but I din't receive any email message from Mach forum. I didn't know about your answer.
Really my steppers are 8 wires, pull out from dot printers, I think they are 12volts 0.75A
My CNC controller only can drive 5,6 and 8 wire steppers, 4 wires is not possible. It's a HobbyCNCPro four axis controller capable to drive four 3A stepper motor in each axis.
Sorry I don't understan whats the meaning of *starving*. English is not my native lenguage, and Iam not capable to understand many words like this one.
I believe that you told me that this connection of two steppers in one axis will not burn my controller because is a chopper drive.. is ok until here?
And bad results can be that current *starving* my motors....¿What meaning this phrase?
Thanks in advance for your help
Regards
Rene
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Hi Rene
Sorry - I missed the fact that your drivers are unipolar.
What I meant by "starving" is "hambriento" (I think). If for example you had 3A motors and 2A drivers then your motors would be "hambriento" for 1A but no damage would happen because the chopper drive wouldl limit it's output current to it's maximum of 2A.
But anyway, your drivers have a maximum of 3A and you'll only need 1.4A for your two unipolar wired motors in parallel (if you're correct about thei motor's phase currents). Just make sure you limit the current of the driver to 1.4A. There should be a way of doing this on your driver board - usually either by changing a current sense resister or via a dip-switch.
Anyway - good luck - like I've said, I've done this on several systems and it's allways worked no problem.
Cheers
Ian
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Hi Sirling, thanks for your help
Can you send a diagram for connect both motors in paralell.?
I suppose that I must too set Vref in controller for two motors in this way (0.75A x 2)= 1.4A x 0.1 = 0.14volts
using one stepper will be 0.75A x 0.1= 0.075volts
I think that if max current in both stepper is less than 3A, steppers will not be "starving=hambrientos" of current
Thanks in advance
Rene
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Can you send a diagram for connect both motors in paralell.?
Just wire the second motor into the same connector exactly the same as the first motor.
I suppose that I must too set Vref in controller for two motors in this way (0.75A x 2)= 1.4A x 0.1 = 0.14volts
using one stepper will be 0.75A x 0.1= 0.075volts
I don't know anything about what Vref is on your driver so I can't help you there.
Cheers
Ian
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Two motors off one driver? Is this for concurrent operation like maybe for two z-axis to cut two pieces concurrently? Why not just use a timing belt between the two? Set it up with a clutch on the secondary axis so you can disengage and spin it to match. If its for some other purpose then obviously my suggestion is a waste of electrons.
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I think you have just wasted some electrons Bob. ;D
Tweakie.
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Hi
Bob La Blonde, thanks for your suggestions
Really, Iam trying to get more torque
because I will use a small steppers pulled
from dot printers. Your advice could be useful
if my steppers are more powerfull
tHANKS
Rene