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Backlash Compensation Help
« on: January 31, 2015, 01:17:12 AM »
Hello Folks!

I seem to be having some issues with getting my backlash compensation to work in Mach3 on my machine. I've tried a bunch of different values and speeds but I can't seem to find any combination that will get it working.

Are there any settings or boxes that I am missing? Of course I checked the box and restarted mach whenever I try to get it working.

Thanks gentlemen!

Offline RICH

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Re: Backlash Compensation Help
« Reply #1 on: January 31, 2015, 06:21:19 AM »
Post your xml file and someone will have a look at your settings.

I have not used backlash in long time because I got rid of it on all my machines. Worth the time and effort!
I strongly recommend you do the same.

The  50-50-50 rule which you may want to consider is as follows:

50% - The max velocity is 50% of where your steppers will start to skip
50% - Set the shuttle Wheel setting in configuration to .0050  to .050 ( .5 too slow )
50% - Backlash speed

The Shuttle Wheel Accel is in seconds. How exactly is the" time" applied to the backlash "cycle"? Well I don't really know.
 It's internal to Mach. By observing the difference in how the motor reacts to different settings you will see that it affects the overall time it takes for Mach to take up the backlash and at say a value of 5 you will find that over five seconds the handwheel / shaft will turn rather slowly. At 0.005 sec its almost instantaneous. In the real slow setting, and say you jog a distance of .1"  you will find there
seems to be almost 3 distinct motor responses in the cycle,....... a small rotation then deceleration...... then backlash taken up
over a time...and then  accel and move to finish the distance.

So to get of flavor of it you need to start slow, observe, listen to see what is happening over an operating range.
Work your way up in settings.

RICH
Re: Backlash Compensation Help
« Reply #2 on: January 31, 2015, 08:46:37 PM »
Thanks for all of the information Rich, I appreciate it! The setup manual for the backlash compensation doesn't delve very deep at all into the specifics of it. I'll tinker a little more and see what I can't mess up.

Preferably I would like to remove all of the mechanical backlash, and I will soon...but for the time being this backlash compensation has been bugging me and I'm more interested in just figuring out what the heck I'm not doing right! The backlash compensation just doesn't seem to apply no matter what I tinker with...

Here is the XML.

Thanks again!

Re: Backlash Compensation Help
« Reply #3 on: January 31, 2015, 09:47:43 PM »
"Hoss" has a couple videos on YouTube that really helped me with backlash.  Here's one:

http://www.youtube.com/watch?v=A27nOkTFYDY
Milton from Tennessee ya'll.

Offline RICH

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Re: Backlash Compensation Help
« Reply #4 on: January 31, 2015, 09:55:16 PM »
See you have BC enabled and have values for two of the axis. 0.0008" is small amount and you will need to realy use a large
shuttle wheel setting to see the BC being implemented.

I assume that you measured BC by moving in one direction, stopping, and then measuring how much lost movement you had
when going in the other direction using an indicator.

Other than that nothing caught my attention in the xml.

BTW, You can't have zero backlash and a lot of mechanical things needs to be looked at very carefullly when trying to reduce
it to under say 0.001". You can have that amount due to bearing preload.

RICH
« Last Edit: January 31, 2015, 09:59:08 PM by RICH »
Re: Backlash Compensation Help
« Reply #5 on: February 01, 2015, 04:41:02 PM »
See you have BC enabled and have values for two of the axis. 0.0008" is small amount and you will need to realy use a large
shuttle wheel setting to see the BC being implemented.

I assume that you measured BC by moving in one direction, stopping, and then measuring how much lost movement you had
when going in the other direction using an indicator.

Other than that nothing caught my attention in the xml.

BTW, You can't have zero backlash and a lot of mechanical things needs to be looked at very carefullly when trying to reduce
it to under say 0.001". You can have that amount due to bearing preload.

RICH

Thanks for looking over my XML. That is how I measured my backlash, as you stated it is .0008 in X and .0015 in Y.

I've got a batch of parts to run that will keep me busy for the next couple of weeks but will delve deep into the mechanical backlash after that.

I was also informed that my version of Mach is a pirated one... I had thought it was just the demo version of mach that my controller included. Perhaps that's where the BC is hanging up. I intended on buying a license once I wrapped my head around the software for the most part, of which is coming up quite soon. So I'll probably get a legitimate license around the middle of the week and go from there.

(No subject)
« Reply #6 on: February 20, 2015, 01:37:00 AM »
Any luck getting your backlash working correctly..... I'm having the same problem I don't know what units relate to in the settings value field....  my backlash is .006 so that's what I enter and I get no change at all..... help!!!
Re: Backlash Compensation Help
« Reply #7 on: February 04, 2016, 11:00:25 AM »
Hey all,

Not sure if this is backlash related or settings but here it is.

As described in a few manuals to test for backlash I run the following code to see if my axis comes back to the correct position.  And it does!!  I can run the 50 times and it works great (the code shows 5).

My question is this:
I noticed that while the axis returns to the correct position it does not come back to zero during the move.  I have posted two videos to show this. One regular speed and one slomo.

Please fire away with comments...

https://www.youtube.com/watch?v=kuv7-VUbzME
https://www.youtube.com/watch?v=hQibCMunpIA


F1000
G20 G90
M98 P1234 L5
M30
O1234
G1 X4
G1 X0
M99
Re: Backlash Compensation Help
« Reply #8 on: February 04, 2016, 11:06:38 AM »
Try it in Exact Stop mode. G61
Re: Backlash Compensation Help
« Reply #9 on: February 04, 2016, 01:06:03 PM »
Works. Thank you!