How do I fix my Oval Shaped Circle

As may be evident from my subject I have made a couple of items (mostly to test capabilities and such, no real projects to be used) and the fact that it was not perfectly dialed in was not an issue. However, now I am trying to make more intricate projects and am wondering how I fix the issue that my maslow likes to cut ovals instead of circles. I used @bar’s new sled .nc file (with the center not cut fully out to be able to mount the bit in the middle for alignment) because I wanted to make sure that I had a good sled and it was not a rotational issue.

While cutting this sled I noticed that it was starting to look like it was not making perfectly circular holes and since then I have finished the cut and measured and to my surprise it is almost 1" different in the dimension. It is 18 9/16" wide and 17 5/8" tall.

What should be the first number that I look to change?
Motor offset?
Rotational radius?
Chain sag?

I am assuming that these would be the place to start. I have also seen on another thread how someone suggested marking a point and moving the sled up 6" at a time and down, I did this and found that the problem gets worse as you get further up from home center (to be expected somewhat) but what surprised me was the actual numbers.

Center mark to mark 1 = 5 11/16"
Mark 1 to mark 2 = 5 5/8"
Mark 2 to mark 3 = 5 1/2"

Any help would be greatly appreciated.

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Being almost an inch off over 18 inches is a huge amount of error. Seeing that kind of distortion says to me that something is WAY off and that we should figure out what it is before we try to tweak any variable.

Did the automatic calibration process go well? Were there any hickups? It might be worth doing that process again as a starting point.

Well, I have been using version 1.11 because every time I try 1.12 or 1.13 I get an error when I try to let out chain to measure and the motor goes the wrong direction. Is there something that I am doing wrong there? I am assuming that I should be on the newest version but every time I have tried to go to a newer one I have had an issue but 1.11 has been solid. Maybe I am updating my Arduino incorrectly? I am not sure but when I go into ground control it says firmware 1.12 or 1.13 after I do that update but every time I update it tells me I need to redo the chain calibration and if I try to do that it will go the wrong direction and so I started at the beginning of the calibration process and put everything in but then the motor went the wrong direction in the extending process to measure the top beam.

Got it! Let’s solve that issue first and get you up to date.

How is the machine set up? Do the chains come off the top of the sprocket to go to the sled or the bottom of the sprocket?

Edit: It might be easier to ask do you keep the slack chain along the top beam or on the sides of the frame?

I am bottom feeding. I have the chain up top (I am going to buy another bungee hopefully tomorrow) I have attached a picture. It is basically completely the stock setup from the most recent run with the addition of 18" of chain per side (from maslow so it should be same pitch etc) and then extra spoil board so that when I go to the outer extents it is not basically at the end of the chain.


Thanks for the picture! That helps a lot. Looks like a really solid build!

Here’s what I think is going on.

I think you are updating the firmware perfectly. That it reports the updated version number after updating tells me all is well there.

When extending the chain to measure the distance between the motors it SHOULD rotate the wrong direction for you. We want the chain to go from the top of one sprocket to the top of the other for that step so the chain has to be on the sprocket in the top feeding direction. After that step the calibration process will ask you to take it back off and put it on the other direction

Thank you! I used your bolt together frame as inspiration. For the chain it should be rotating in toward the right motor, but it rotates out for that portion so when I put the chain on the outside of the sprocket it throws the chain off.

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Woah! That is very strange.

That’s exactly what I would expect too:

When you press the Test Motors/Encoders

Does the left motor rotate when it says “testing left motor”?

I updated to 1.13 and then here is the error I get (I assume is normal) and then on the right I can see that it is updated on Arduino.

When I test the motors, both the left and right motors move in first and then out.

Edit: I am now going through the whole calibration process and when I get to the point where I should be making the sprockets point 12 noon to 6. Neither sprocket will move, they will make the noise but nothing happens.

Edit 2: If I skip that step and move onto the next one to motor out the chain length that is when the left motor goes out away from the right motor.

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Ok, let’s check the sprocket direction setting. It’s under advanced settings here:

Does changing that setting reverse the direction?

It appears it was set to “top” even though in the setup process I clicked bottom on that beginning section. Checking to see if this changes anything.

Edit: After changing to to bottom, the screen where I align the cogs it is moving however, it is moving CW when I click on CCW.

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I will look into see if there is a bug which is making the calibration selection not show up in the settings right.

Does the chain go the correct direction when extending it even if it’s the wrong direction for the set sprockets?

I also noticed that when I am trying to move the sprockets it is moving probably at least 10 degrees no matter what button I click and always moving in the CW direction for the left motor. When I skip that step and go to extend the chain it still moves the wrong direction.

I also just had my GC freak out and start throwing warnings when I went back and clicked the buttons to align the sprockets I got these 2 errors flashing back and forth (with the motor running and not stopping) until I killed power.

I’m trying to replicate the same behavior and I’m seeing some strange things happening too. Let me see what I can figure out

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I think after switching from top to bottom configuration the arduino may need to be power cycled. This used to be the case, but I though we had it fixed. Try closing ground control, unpluging the Arduino for 10 seconds and then starting over

Thank you so much. Sorry to be the bug catcher, that is why I went back to 1.11 haha. Probably not the correct decision, next time I will just ask on here first.


Being the bug catcher is the best! We’ve got to catch them all!

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Bar, I just went back and made sure that it was set to bottom in the advanced, turned off both the control board and Arduino for 10 seconds and restarted GC. I started the calibration process and skipped until the sprocket alignment and now the right motor is not moving at all (nor making noise) and the left one makes some noise but will not move either. The noise on the left motor is less than usual as well.

Edit: Also, if I skip the alignment step and go to the next one to feed the chain through to measure it makes a noise but the sprocket still will not move.

:frowning_face: Well those are none of the things we want to be happening

Ain’t that the truth.