Ground Control calculated distance between motors different than tape measured distance

During the calibration process using the chain to measure the distance between the motors, Ground Control gives me a distance of 2846.81mm. The same distance with a tape measure gives me 3176mm.

I’ve done the calibration twice. I think I’m following the correct path.
Starting with first link of the left chain on the top tooth of the left motor, hanging down off the left side of that sprocket. Bottom feed - ‘Extend’ the chain from the left motor across to the right motor then ‘Pull it tight’ before clicking ‘Measure’.

This means Ground Control is 329.19mm (12.95inches) short!
What am I doing wrong? Thanks!

Ground Control V1.20
Arduino Firmware 1.20
Windows 10
Motors from Maslow (


Is that the original chain? (pith 6.35)

The chain is #25 from Amazon. (pitch .250inches)

The sprockets on the left and right motor shafts are #25, 11 tooth. (

Wrong chain?

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I’m not an expert, but the distance per rotation might be a clue. In the groundcontrol.ini -> distperrot = 63.5. You could use the ‘set sprocket to 12’ from the calibration to rotate a full turn and measure the chain feed.

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Have you changed the value of Settings/Advanced/GearTeeth from the default 10 to 11? That could make a difference…


My chain stretches at least 3mm on the ‘pull tight’. I have a 2x4 as top mounted the same way you did and after making it “rock solid” it still flexes 2mm. My motor mounts don’t flex after I modified the mounting. I would expect yours to flex a few mm. That all only would add up to max 10mm and not to the amount you are seeing.

I don’t have a Settings/Advanced…

I have an Actions/Advanced but no GearTeeth in there.

The menus in Kivy aren’t as clear as they should be… :pensive:
To the right of the word ‘Actions’ is ‘Settings’. Once that is clicked, ‘Maslow Settings’ comes up. Now click on the words ‘Maslow Settings’ to see a dropdown list of other settings pages - ‘Advanced Settingsd’ is there.


Holy shit…

Given to you, much power is - it wisely use!  <(-_-)>

measure with the tape measure while it’s under load, I’ll bet that you see a air
amount of flex at that time compared to measureing while it’s slack. I expect
that those mounts will flex more than you think

but a difference of 300mm is insane, that’s a foot of difference

check what it reports before you do the calibration calculation, I think the
calibration routine will adjust the motor spacing value to try and make the math
work out, and that’s clearly very wrong in your case.

David Lang

I was not seeing that the “Maslow Setting” bar was clickable inside of settings. @blurfl was correct. Thank you guys for your time.


Suspect this is a circumference of the sprocket issue.

@blurfl got me squared away however after I’m still coming up short using the chain to measure. Ground control measures to 3130mm. Tape measure gives me 3176mm.

I got fed up and now trying manual calibration with inaccuracies still.

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I struggled a lot with the calibration also.

What I have observed, is that the machine is pretty good at hitting the geometric center of the 4x8 plywood sheet after the last step (when you put in the distances between the cuts).

I drew a grid on the plywood before starting and have “sent it manually” to many of the intersections. It gets there and gets back “home” just fine.

Any distortion or travel distance discrepancies?

Not that I have found so far

Allright that’s good know!

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Updating thread…

After changing Maslow Advanced settings tooth count to 11, my accuracy has improved.

Ground Control’s calculated value is at 3136.58mm and my tape measured value is 3146mm (different from my first measurement due to me messing it up).

Is it good enough to be off by 10mm?


no, override the calculated value with the measured one.

This is common, we know the cause, but have not figured out the proper fix for

David Lang