Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: AlbertaClipper on August 10, 2011, 11:01:23 PM
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I built a CNC router with rack and pinion axis. I want to slave my X axis and its parallel A axis. I bought cncrouterparts rack and pinions. When I move the X axis both motors move in the same direction...as they should. The problem is when the motors are mounted on the machine the face each other so when one motor is going north the other is going south. How do you change the direction of A axis so that the motors move in the same direction when mounted on the machine?
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Change the active state of the Dir pin or change the Reverse option on Homing and Limits page (from Config menu)
Other option is to swap round wiring on the motor/drive.
Hood
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Hi Albertaclipper,
I run a slave axis and I have set X & A in Mach3 to mirror each other (much simpler for my tiny brain to comprehend) and have just swapped the wires to the motor B+ & B-.
I had concerns recently about one motor stalling and the other continuing and doing unspeakable damage to my gantry. I have updated my drivers to ones that have a stall detect on them - which is is wired back into the E-stop. My motors have drive shafts on both sides. The outsides are driving my axis and I have connected the insides together with a shaft, the idea behind that is that if one starts to labour a bit the other one will help keep it running, kinda like hooking up two locomotives in tandem. Maybe a bit of overkill, but it works.
Cheers
Rod
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Thanks guys for the replies. Changing the Dir active low did the trick. I don't know why it didn't last night when I tried it but it works now. Thanks again.
Mike
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The outsides are driving my axis and I have connected the insides together with a shaft, the idea behind that is that if one starts to labour a bit the other one will help keep it running, kinda like hooking up two locomotives in tandem. Maybe a bit of overkill, but it works.
Rod,
Have you used a flex coupling between the two motors ??
Tweakie.
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Hi Tweakie,
The couplers are solid. I figured there wouldn't be any load on them or the connecting shaft whilst they are running in sync unless one motor stopped then it does its thing. The other side of the motor is connected directly to pulleys via a keyway which run the belts. You've got me thinking now whether there might be load on them when changing dirertion but then again they are being driven by both sides. Hmmm - what do you think?
Cheers
Rod
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I was just curious because I never got this type of setup to work successfully, I suppose it depends on the manufacturing quality of the motors but they were always trying to bounce off each others indented position except for the few places where they matched perfectly. I since thought that a flex coupler may have solved the problem but changed the design before trying it.
Tweakie.
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.........and I have connected the insides together with a shaft, the idea behind that is that if one starts to labour a bit the other one will help keep it running, kinda like hooking up two locomotives in tandem. Maybe a bit of overkill, but it works.
It's probable more likely to stall with the motors connected, as they'll always be fighting each other slightly, as Tweakie said.
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I appreciate the feedback, I had read about this connection and the thought of crabbing the gantry did inspire it but the thought of perhaps causing the train wreck has just inspired its benching until I find out more. My table is in its final stages of testing before I push the go button. The axis has been running smoothly with the connection but I haven't run it under working load yet, not really prepared to take the chance now. I have upgraded the drivers to a higher output and they have a stall detection feature on them, my original drivers were causing grief with motors stalling at full speed - which doesn't happen now with the new drivers.
That in itself drove me a bit whacky as I couldn't understand why - if each motor is powered by a separate supply and driven by it's own driver - would it only occur when two or more axis were running at full speed.
This is a great reason to be active on this forum, the feedback is invaluable.
Cheers
Rod
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my original drivers were causing grief with motors stalling at full speed
How did you determine what "full speed" was?
To safely run a stepper machine, you should be running at about 75-80% of the point where stalling occurs. Running faster is asking for trouble, as the point where stalling occurs can vary with changes in lubrication, temperature, and other factors.
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Hey Ger21,
I followed the Mach setup videos & doco in conjunction with the motor and driver recommendations. Full speed is just my way of saying "jogging at 100%". I am happy with speed of the motors which is well inside the maximums for the motors. My motors were stalling at that speed only when 2 or more of them were running. Thanks to the forum I changed some Mach settings and that helped a lot but at 100% jogging rate they were still stalling from time to time albeit a lot less. That's when I added the connecting shaft on the X motors and upgraded the drivers. Had no problems since, but the shaft came off this morning.
Cheers
Rod
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Hey Ger21,
I followed the Mach video & doco in conjunction with the motor and driver setup information. Full speed is just my was of saying "jogging at 100%" I was happy with the motor speed - which is well in side the recommendation for the motors but when I engaged two or more motors at that speed one or more of them would randomly stall. Thanks to the forum I changed some Mach settings and that helped a lot but the stalling still occurred albeit a lot less. That's when I upgraded my drivers and installed the connecting shaft, had no problems since but the shaft came off last night.
Cheers
Rod
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which is well in side the recommendation for the motors
It's impossible to recommend a speed that steppers can be run at, unless the exact steppers, power supply, and drives have been tested on the exact machine you'll be using.
Every machine is different, and the only way to determine the top speed is trial and error.