Is there a kinematics calibration guide?

Good point. The question would then be, was the part cut in the vertical orientation? If so, that may hint towards calibration issues.

Before the update to V1.00, I was experiencing a similar issue to @Onelonedork’s problem. I was able to get it within 3mm tolerance but couldn’t get it any tighter than that. After the update, I was able to get it to ~±1mm in a couple of tests. I still plan on trying to dial it in more than that.

I have done calibration routines ad nauseam with the top mount linkage system. Full disclosure, I don’t use the auto calibration process. I think my machine is not physically long enough, because everytime I’ve tried to use it I end up going in the wrong direction. I’ve come up with a manual calibration process that involves cutting squares, measuring the results, and tweaking the motor distance and the rotation radius. Those two values have the greatest impact on machine calibration. The simulator is a great tool for testing which calibration values are messing you up. I’m guessing you might be having an issue with the rotation radius, since you had the machine working well with the stock kinematics. It’s hard to say, however, without being at the machine.

Compounding errors are quite easy to calibrate around and get center of the machine cutting at least as accurately as ±1mm. I’ve seen some distortion to the far left and right sides of the bed, but that also could be because I have a short machine. My efforts to test compounding errors further (in the manner @dlang has suggested) are moving at a glacial pace. Especially because my shop hasn’t been above 20 degrees for a few weeks now. The last thing I cut was the HDPE pad for the bottom of the sled, so I’m getting close to putting together the test sled. Here’s hoping things warm up for a week or so that I can get more definite numbers.

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The part was cut vertically, i’ll post my settings shortly as well as some photos. I’ve cut the part across in multiple spots across the 4x8 space. Comes out the same everywhere, always short by about an inch. I’ll start over with calibrations (round 10).

when you do this round of calibration, put a tape measure between the motors
before you start, and again while the chain is pulled tight, see if there is a
difference between the to measurements.

I’m thinking calibration process issues here.
I’m using a top-mount kit like the one pictured. I just did a full calibration using v1.02. I checked that the motor spacing (3365.37mm) under load matched the motor spacing at rest. The rotation disk radius after the calibration (116.815mm) is the same as the previous time I did the calibration. This calibration gave 1905.2 on the first cut. This value for rotation radius seems odd, as David’s esitmate for the value was 133.35mm or 136.525mm. I’d like to see a diagram that shows just what is being measured here. At any rate, the calibration test passed, so the machine should be accurate.
As a test, I ran 20" up from the center position and made a mark, then 40" down and made another mark, then back to the center position. It returned to the center position precisely. The upper mark, though, was 19 15/64" above the center, and the lower mark was 19 47/64" down.
Moving 37.5" to the left and right to make the same pattern yielded similar though slightly different results. The bottom marks lined up across the sheet, the left and right center marks were 5/64 above the center mark, the left and right top marks were 19/64" above the center top mark. I pulled the sled down and vewrified thatn then center of rotation for the

I’m thinking calibration process issues here.

I’m using a top-mount kit like the one pictured.
I just did a full calibration using v1.02. I checked that the motor spacing (3365.37mm) under load matched the motor spacing at rest.

That is a little wider than a stock frame (just over 11’), but not unreasonable.

whenyou say the spacing under load matches the spacing at rest, do you mean that
the distance measured here matches what you get from a tape measure, and that
there is no difference between under load and at rest ith the tape measure.

The rotation disk radius after the calibration (116.815mm) is the same as the previous time I did the calibration. This calibration gave 1905.2 on the first cut.
This value for rotation radius seems odd, as David’s esitmate for the value as 133.35mm or 136.525mm.

that is odd, 116.815mm is 4.6" and the horizontal links in the kit are 5"

This is an impossible value for this kit and means that something else was
measured incorrectly, and the ‘calibration’ is trying to correct for the error
(see more details below)

I’d like to see a diagram that shows just what is being measured here.

The rotation radiuks is the distance between the end of the chain (more
precisely the center of the hole for the pin at the end of the chain)and the
center of the bit. With this kit, this is 5" (the length of the horizontal arms)
plus 1/4" (the length of the master link that’s added to the chain)

but it’s not actually being measured, what’s happening with the current
calibration routine is that it makes cuts that should match if the yoffset
height and motor spacing are correct, and then ‘adjusts’ the calculated rotation
radius to counter whatever error you find. If the motor spacing isn’t correct,
then the rotation radius that’s calculated won’t be correct (I suspect that if
the yoffset value, the height of the motors above the work area, is wrong, that
will also throw off the calculations)

At any rate, the calibration test passed, so the machine should be accurate.

yes and not, it’s introducing error in one measurement to counter errors from
other measurements. The fact that it ended up with an impossibly small rotation
radius for this kit means that something else is off.

As a test, I ran 20" up from the center position and made a mark, then 40"
down and made another mark, then back to the center position. It returned to
the center position precisely. The upper mark, though, was 19 15/64" above the
center, and the lower mark was 19 47/64" down. Moving 37.5" to the left and
right to make the same pattern yielded similar though slightly different
results. The bottom marks lined up across the sheet, the left and right center
marks were 5/64 above the center mark, the left and right top marks were
19/64" above the center top mark. I pulled the sled down and vewrified thatn
then center of rotation for the

and this confirms that something is off.

Yes

Hard to see why that would be; it should only affect the vertical location of 0,0 on the workarea.

and that is the reason for the post :smile:

Hard to see why that would be; it should only affect the vertical location of 0,0 on the workarea.

not quite, you are trying to calculate a triangle

the horizontal part is half the distance between the motors

the vertical leg is the Y location + yoffset

and the angled leg is the chain + the rotation radius

so if yoffset is off to far, it will affect the calculated rotation radius
calculation

Untitled
So I finally had time to run through calibration a few more times. The cuts are actually getting worse. After two more trips through calibration, I’m not more than an inch and half shorter than stock Maslow.
20180101_150630
I also measured between motors with chain and only ended up 1mm different from my tape measure which I calk up to the looseness of the metal tip. Any other ideas?

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I’ve had disappointing results from the automatic triangular calibration, too. Much better when I entered the value by hand. For the linkage shown in your picture (like mine as well) 127mm is the appropriate value. Still not perfect, but not 1" off over 6" distance :smile:.

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It’s gotten worse, which means my changes have made a difference. These last couple of chain calibrations, my chain has also been putting the center point of the work piece a foot or so low.

try removing your .ini file and starting from scratch

or try zeroing out the distance between mounting points, vertical distance mounting points, and CG values

we’ve seen that something seems to be still using those values if they are defined.

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Thanks dlang, i’ll give it a try.

also, are you in inches or mm for the calibration steps?

I’m using millimeters

you may want to also try the calibration spreadsheet at

and then enter the values manually

This is an experimental process, but the math says it should work, and since you
are having problems with the standard calibration…

But first clear the .ini and try from scratch

one other thing, if you are in triangular kinematics, it should not be showing
you the settings you show in the screenshot, it should be showing you a shorter
list that has rotation radius.

it looks as if you are not actually in triangular kinematics

Be careful here - the image shown is as seen for both quad- and triangular choices. The triangular choice is on the Advanced Settings panel, not shown above.

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The spreadsheet requires the user to enter the programmed chain length for the two cuts. I’m not certain that these numbers are readily available on a standard installation at this time. I’d welcome correction, though :wink:.

But the screen that’s shown does not give the option to set the rotation radius.

That’s right, that setting is on the Advanced Settings screen, right the Quad/Triangular choice. Investigate, don’t speculate…