What must be adjusted to correct out of round circles

OK, here are the results of my Benchmark Test…

Looks pretty terrible to me…

Here is the latest .ini file from calibration today…

groundcontrol_4-22.ini (1.4 KB)

Here is what I did today…

  • Recalibrated using V 1.11 of both firmware and Ground Control on Windows 10
  • Used my measured distance between the outsides of the motor gearboxes minus 40.4 (3006.012)
  • In the process I used the Maslow to measure both the Left & Right chains - (L = 3001.8, R = 2997.15)
  • Used 140,7 for the rotation value (result of previous calibration)
  • Ran the triangulation cut file and entered the values
  • Set up the machine and cut some 6" circles, which were all pretty dead on horizontally, but short about 1/8" vertically.
  • Played with the Chain Pitch to compensate for Maslow’s chain measurement error until I got mostly round circles (6.368 pitch)
  • Ran the above Benchmark test.
    Speculation… Perhaps with the adjusted Chain Pitch, I should use the Maslow Measurement, but which one?
    Perhaps the Chain Tolerance adjustments should be made instead of messing with the chain pitch?

Yes, I am in the weeds w/o a mower


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Considering the chain tolerance adjustment as the way to deal with what the Maslow thinks the chain length is, rather than messing with the chain pitch…
@dlang suggests making the tolerance adjustments by comparing the man and Maslow measurements, figuring the tolerance percentage, entering it in Settings, and measuring via Maslow again to confirm that Maslow agrees with Man…

To get to this adjustment, is the following correct?

3006.012 - 3001.8 = 4.212
4.212 / 3006.012 = .00140119
1.00140119 x 3001.8 = 3006.0061, pretty close to 3006.012
So, for the left chain, use the 1.00140119 (or just .00140119?) as the left chain tolerance, and use the Maslow to remeasure this chain, hopefully getting the correct number.

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From looking at that test I’m seeing a score of 7.5-1.4 while a good score is about 1-1 right now so that 7.5 is pretty bad.

What seems really strange to me is that you are seeing mostly distortion along the y axis when cutting circles, but in the test results we’re only seeing 0.1125mm of distortion over 900mm which is great!

I think that is what we should try to figure out first

Keep in mind that I adjusted the chain pitch to 6.368 from 6.35. I arrived at that number through trial and error mostly. When I tried numbers over about 6.373. the distortion started to reverse, with the width getting smaller and the height stabilizing around 6". What do you think about returning to the default chain pitch and working to get the Maslow to correctly measure the chains?

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We’re in a little bit of uncharted waters here and we’re still figuring out what the right way to do things is.

I saw you mentioned in a different post that you are measuring out different lengths on the left and the right, is that what you mean?

Yes. I used the Maslow to measure both chains… Left came out 3001.8, and right was 2997.15

Seems like these inaccuracies, if consistent, could be part of the problem. Can the Maslow measurement tool be used repeatedly, or do the cog’s need to be 12 o’clocked after each test?

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Can you do me a favor and mark which tooth is at 12 when you start and do the process without the chains attached to see how much each motor rotates? I think we should track this down before we do anything else.

OK. I will get back to you asap.

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So I have the two motors at 12 oclock… should play out the chain to set up the machine for tensioning, getting the chain as tight as possible, then taking the chain off and marking the teeth. Or do I mark the teeth now and tell the machine to tighten the chain without the chain on?

I was imagining using the Set Chain Lengths Automatic widget to pay out the chains and measuring that one is the same as the other, but I’m open to suggestions and think maybe I was misunderstanding.

Are you seeing a different measurement between the motors using one chain, vs the other?

Using the “chain to measure the motor spacing” tool in the Calibration routine, I used both the left and right chains to see if they were similar… they were not, with the left chain at 3001.8, and the right at 2997.15

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Yes. I used the Maslow to measure both chains… Left came out 3001.8, and right was 2997.15

this is why there are separate left and right chain tolerances :slight_smile:

Seems like these inaccuracies, if consistent, could be part of the problem.
Can the Maslow measurement tool be used repeatedly, or do the cog’s need to be
12 o’clocked after each test?

yes the measurement can be used repeatedly, but you need to set the cogs to 12
o’clock at the start of each test so that you are starting at a known position

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Got it! Cool test…I hadn’t thought to compare like that.

That sounds like you are on the right track in the other thread of changing the chain pitch.

So thinking out loud then, maybe we need to switch to measuring outside edge to outside edge on the motors, then do the pull chain tight measurement from each direction and instead of using that to decide the motor spacing, use it correct for the actual chain lengths?


If you think it is worth a try, I would

  • return the chain pitch to default
  • calculate the Maslow motor spacing again using both the right and left chains
  • create the correction value for each chain by taking the difference of each chain from the actual measurement, dividing that difference by the actual length, and using those results as the correction value
  • enter these values in the “chain tolerance” setting for each chain
  • return to the Maslow motor spacing routine and do the calculation again

Hopefully they will return more correct values.

Does this make sense, and do you think it will help with the circles?

Any suggestions on streamlining the Motor Spacing measurements? Seems like for every chain I will need to get to 12 o’clock on both sides, do the routine, then advance a couple of steps to see the result.

Once all lengths are close to matching, I should be able to do the manual calibration, then the triangulation, then the benchmark test… do you see a better way?


Yes!! I that would be so much appreciated!

I can’t answer if it will help until we try it, but I expect it will!

One more thing to try might be to check that measuring the distance between the motors gives the right value after adjusting the “chain tolerance” setting. I expect it will, but it’s a good sanity check that we are on the right path.

Other than that I agree with your plan entirely


@bar, @Dustcloud has beat me to it but this was what I envisioned. So we don’t have to swap chains from left to right it would be nice to have the ability to do the chain tension routine from either side.

What you just described is perfect!


Adjusting the chain tolerance for the left chain did correct my automatic measurement to within a tenth of a mm repeatedly. So it wasnt a fluke. I expect to see the same for @Dustcloud. I think @Bee or @madgrizzle may have done this as well?


So, I entered the corrections into the Chain Tolerances, left and right…
L .00058248 x 100 = .058248
R .00213065 x 100 = .213065

Going to the my 12 o’clock centered sprockets (already done), I ran up the left chain to the right sprocket, got it tight, and pressed the “Pull Tight”… the chain flew off the right side. This had not happened before, but, there is always a first time. So I go to set the 12 o’clocks, and no problem with the Left, but the Right turns the opposite of the commands, and moves further than normal. So, I am thinking the chain was dropped because the right side is now going the wrong way.

So, I reset the chain tolerance on the right chain to 0, and now it works fine. So, what now, team?


I can’t remember if I’ve mentioned it before, but during calibration of my machine the subject of chain pitch came up, so whilst the chains were off at one point I laid them out on the floor and measured 100 links. That gave me a chain pitch that was more like 6.343mm (IIRC). Doesn’t seem like a major difference, but when you’ve got over 2 metres of chain in play it’ll have a bearing.


Thanks for chiming in! This is all helpful data. I think it really does make a good case for adding an automated chain pitch measurement and verification step like bar described above.