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Steps per Inch Question with Slaved Axes
« on: March 04, 2021, 08:00:13 PM »
Hello,

This is my first post, and I'm happy to be here.

I have a larger gantry machine with two motors, one for each side of the gantry.  The left is set to the Y axis, and the right is set to the A axis slaved to the Y.

My problem is that the A axis moves slightly less than the Y.  Over a 40" travel, they differ by about 0.03" (measured by linear glass scales).

I attempted to adjust the steps per inch of the A axis independently of the Y to compensate, but the changes I make to the A axis motor tuning have no effect.  The Y axis motor tuning settings apparently affect both Y and A.

Is there a way to independently adjust the steps per inch of a slave axis in Mach3?  Or is there another way to compensate that I haven't thought of?

Thanks in advance, and looking forward to future discussions.

Mark
Re: Steps per Inch Question with Slaved Axes
« Reply #1 on: March 04, 2021, 08:11:50 PM »
Hi,
to my knowledge a slave axis must have identical 'steps per unit', max velocity and acceleration as the main axis.

Is there a mechanical reason one motor should not move as far as the other despite turning the same angular amount?

Craig
My wife left with my best friend...
     and I miss him!
Re: Steps per Inch Question with Slaved Axes
« Reply #2 on: March 04, 2021, 08:17:26 PM »
Hi,
to my knowledge a slave axis must have identical 'steps per unit', max velocity and acceleration as the main axis.

Is there a mechanical reason one motor should not move as far as the other despite turning the same angular amount?

Craig
Thank you for the reply.  I assume the slave should have identical settings for identical operation as the master, but this isn't the case.  Both sides use the same hardware.  Measurements on both sides are repeatable, but slightly different.  Upon further reading, I encountered information indicating that the real-world non-ideal characteristics of the components can lead to errors like this.  I can think of no other reason for the discrepancy.  Nor can I find a method to correct it.
Re: Steps per Inch Question with Slaved Axes
« Reply #3 on: March 04, 2021, 10:53:22 PM »
I just read the Mach4 manual, which explicitly states that you can set multiple motors to a single axis, and set each motor to have a different settings, including steps per inch.

This leads me to believe that Mach3 cannot do what I need it to do.
Re: Steps per Inch Question with Slaved Axes
« Reply #4 on: March 04, 2021, 11:14:09 PM »
Hi,
I've been using Mach4 for six years, and I know that there is a vastly better and more flexible method for slave motors.
My machine does not have a slave axis and so I can't comment on whether it is possible to have different settings for each motor
on a multi-motor axis, if had had been left to guess then I would have said no, you could not do that....but the truth is I don't know.

What is true is that you can programmatically link/unlink motors on the fly, change settings programmatically and various other clever
options that come about because of the architecture of Mach4/Lua, and would surmise that what you want to do is possible, even if the direct
method is not possible.

Mach4 is a learning curve, and many get frustrated while learning and quite a few give up. Those who persevere do end up with a vastly better
CNC solution than Mach3.

Craig
My wife left with my best friend...
     and I miss him!
Re: Steps per Inch Question with Slaved Axes
« Reply #5 on: March 04, 2021, 11:29:06 PM »
Thanks.  I'm going with Mach4.  From what I've read, it can do what I described above.  But I need to finish my Smooth Stepper system and cut the enclosure with Mach3 first.  I can't believe that any software could be more frustrating and clunky than Mach3, and I figured it out ok.  I just hope that Mach4 releases are more stable.  Each new Mach3 release seemed to introduce new problems.  I'm also looking forward to ditching the parallel port.
Re: Steps per Inch Question with Slaved Axes
« Reply #6 on: March 05, 2021, 12:53:04 AM »
Hi,
I found that Mach3 worked, but yes it had bugs. When I started trying to code my own macros however I 'spat the dummy' at
VB, or rather Cypress Enable that Mach3 uses as scripting language. I thought if I'm going to invest the effort to learn a new
coding language I should learn Lua as it was going to last whereas Mach3 and VB are in their sunset years. Ergo I adopted Mach4.

Mach4, at least to start with, is a quite a challenge....but well worth it. By and large it is stable and few bugs.

Mach3 evolved and grew haphazardly over the years, often with new features braking old ones, or relying on 'dodgy' practices,
and as a consequence Mach3 is/was a nightmare to support.

Mach4 on the other hand was designed. It has a clearly defined structure and protocols that allows development without screwing
other parts up.

Mach4 all but relies on an external motion controller. There is a parallel port version for Mach4 called Darwin ($25 license fee applies),
and as good as it is it misses on a lot of realtime supports like lathe threading, realtime THC etc. Darwin is fine if your on a real tight
budget but otherwise best avoided. Aside from anything else Darwin still requires a 32 bit OS, Windows 7 or earlier to run.
Compare that to any of the half dozen or so Mach4 ready motion controllers and they will all run on 64 bit OS's including Windows 10.

When I took up Mach4 I also got an Ethernet SmoothStepper and while it took a bit of effort to set it up initially it proved to be a huge step
up in smoothness and reliability of operation over the parallel port I had been using.

Regrettably my ESS is still just nailed to a piece of wood, I did that as a temporary measure six years ago and it still like that!
'There is nothing so permanent as a temporary measure.'

Craig
My wife left with my best friend...
     and I miss him!