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Slaved Axis Direction
« on: August 10, 2011, 11:01:23 PM »
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?

Offline Hood

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Re: Slaved Axis Direction
« Reply #1 on: August 11, 2011, 05:17:25 AM »
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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Re: Slaved Axis Direction
« Reply #2 on: August 11, 2011, 07:52:49 AM »
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
Re: Slaved Axis Direction
« Reply #3 on: August 11, 2011, 11:00:42 PM »
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

Offline Tweakie.CNC

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Re: Slaved Axis Direction
« Reply #4 on: August 12, 2011, 05:15:22 AM »
Quote
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.
KEEP SAFE !

BoatBuilder

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Re: Slaved Axis Direction
« Reply #5 on: August 12, 2011, 06:55:46 AM »
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

Offline Tweakie.CNC

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Re: Slaved Axis Direction
« Reply #6 on: August 12, 2011, 07:31:37 AM »
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.
KEEP SAFE !

Offline ger21

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Re: Slaved Axis Direction
« Reply #7 on: August 12, 2011, 08:54:02 AM »
 
Quote
.........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.
Gerry

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BoatBuilder

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Re: Slaved Axis Direction
« Reply #8 on: August 12, 2011, 10:24:36 AM »
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

Offline ger21

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Re: Slaved Axis Direction
« Reply #9 on: August 12, 2011, 11:49:03 AM »
Quote
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.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html