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gavinpoyner
04-04-2012, 10:35 AM
Hello Everyone,
I have made a gantry mill which has one motor running both ends of the Y axis; the motor sits mid way between the Y axis rails (1.5m apart) then it has 2x45' cogs to transferring the rotary motion to the worm Y axis. The problem is the back lash leaves me with flats on the top or bottom of any circles ect. I could use the compensation setting to over come some of it but would prefer to reduce it by better engineering (I am a stonemason, so its a miracle it works as well as it does). So I was wandering about the possibility of using two stepper motors one at either end of the Y axis, and if this is a good option how would I do it?
:)

UUU
04-04-2012, 01:12 PM
You don't mention which control software you are running, or much other details about your set-up. Mach3, for example has facilities to slave two axes together, so assuming you're not already using A, you could partner this up with Y so the two operated together. You need another motor, of course, and another motor driver - and hook this up through your existing BOB set-up (again assuming you have a spare axis route here). Hope your power supply has the necessary capacity, or this may need upgrading.

You'll see all sorts of threads on problems with slaved axes - I'm taking theoretically, because I've not tried it. Let's see if we can get a contribution based on experience.

gavinpoyner
04-04-2012, 03:45 PM
Thank UUU, for your reply. The control software is Mach3, but the controller only has X, Y and Z. I was hoping for something like two motors wired to run from the one output, even if it meant buying two motors at half the rate of the one I am currently using!!
I can supply more info tomorrow, when I be back in my workshop/shed.

wmc01
05-05-2012, 11:16 PM
I am interested in doing the same thing without using Mach3 slave drive. I would like to see if I can run two motor drives with one output from Mach3 to accomplish this.

UUU
05-06-2012, 05:29 AM
I'll post again on this one - although I repeat that since I've not tried this I'm talking in theory. People who've tried this are encouraged to respond, please.

If you use two motors on one driver unit, they'll try to fight one another. The back-emf from one motor will try to drive the other and vice-versa. So this is not recommended.

I don't know if it's possible to use the same step/dir outputs from the BOB to connect two driver units. Would they need buffering up?

johnsattuk
05-06-2012, 09:32 AM
If you use two motors on one driver unit, they'll try to fight one another. The back-emf from one motor will try to drive the other and vice-versa. So this is not recommended.

I don't know if it's possible to use the same step/dir outputs from the BOB to connect two driver units. Would they need buffering up?

I am using the same step/dir outputs on two drivers, I reverse the motor wiring on one because I am running geared motors back to back on a rack driven gantry. I have double shaft motors and use the rear shafts coupled together through a cross shaft. Because of the 50:1 gearboxes I do run the motors at up to 3000 rpm

I have used Mach3 and a std cheap BOB with no problems driving two drivers. I have recently converted to USBCNC system also without any problems.