Any guesses as to discrepancy in arm length vs. measured arm length?
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I think the 80 steps versus 80.5 depends on belt tension if tight its not an issue.
I wonder if a suitably rigid mechanism could be devised like a turnbuckle to lengthen/shorten rods as needed?
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I tested belt tension from what I'd consider fairly loose, to as tight as I'd normally go, and saw far less that a .5mm discrepency in steps/mm. less than 80.1 consistently. Perhaps I'm not going as loose or tight as others might in their tests, but it seemed a good range, and didn't account for the problem. (also, I could measure it, see I was under 80.1, but only fix it by going up to 80.75 or so, which threw my height of objects way off)
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I also did some more testing yesterday and used a 20x60 extrusion and the fsr sensors to be able to measure two different heights as proposed by dc42.
I also have the issue of crazy wrong rod length proposed by s7 calibration and for me, the measured height difference between measuring the 20mm vs. the 60mm side of the extrusion is 39.98, so I guess I can say that my steps/mm are close to perfect.
What I can do furthermore is replace the duet with a smoothieboard to see if this changes anything and I will also print a larger effector to see if effector size plays a role in this game. Glad that tightening the belts is already out of the equation, one step I do not need to do now. ..
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I've changed to a much larger effector, didn't make much difference.
I highly suspect that if I went to longer arms (around 325mm) with the magballs, the issue would vanish, or nearly so, even when probing to the edge of the bed.
First I want to rule out the carriage system entirely, which I'll be doing in the not too distant future I hope.
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Hmm… I have quite long arms, 360mm for a 300mm bed, sorry to tell you I see the issue
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That's helpful! This is a rostock max? What effector and carriages? What arms?
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It's a homebrew printer, but I use the same rostock max effector (I liked the design) and 360mm tricklaser rods with ball cups. The carriages run on MGN-12 rails.
The distance between the middles of the white bar-bells on the carriages is approx. 330-335mm
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I'd be more inclined to rule it out if the arms didn't have springs between them for tension. That's why I want to test with longer magball arms.
I'd be curious to see the output of a S-1 calibration on your printer (after you've done a few rounds of S6).
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Btw, the reason I'm against the springs between arms (at least as far as diagnosing / testing this issue goes) is simple - they change your calibration. If you put the "heavy" springs on, and calibrated your printer, look at the outputs of M665 / M666 and an S-1 probe… then swap to rubber bands or lighter springs, repeat an S6 (or several, so it "settles), and compare the new outputs of M665 / M666 and an S-1, you'll find things change quite a bit. That means there's no way the springs themselves aren't having a measurable effect on your calibration values.
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I had another look at data I collected yesterday and collected some more data today.
Yes, I agree, there is an influence of the springs, but I guess it is not very relevant.
What I did yesterday was checking probing speed / motor power vs. deviation of testresults.
So I did a log of G32 runs with S-1 to collect the data. I varied probing speed and current for the motors, I saw a big influence of the motor current with the default probing speed of F120 when choosing 1.5 or 2A current, but with the default of 1A there was not much to see at different probing speeds.
What is relevant in this context is that I measured the deviation of the results of each probing point, if springs have a huge impact that deviation in the points should be higher than the measured 5-7.5 Micrometers, shouldn't they? unless of course that because of the quite repetitive movement pattern the effect of the springs is always the same, but I kind of doubt that.
Today I also did some more measurements with moving the head arround and then probing x0 y0, here the numbers are also quite close:
Probe with moves on Bed Probe with moves on 60mm Probe without Moves 60mm Probe without moves 20mm 0.07 59.914 59.939 19.97 0.077 59.914 59.927 19.977 0.07 59.914 59.933 19.977 0.07 59.895 59.92 19.97 0.064 59.914 59.914 19.97 Avg 0.07 59.91 59.93 19.97 Dev 0.00 0.01 0.01 0.00 -
The effect of heavier sprints is to pull up on one corner of the effector at the point when it's between towers. This is easily observed - if you take a set of barbells off your printer and put your arms on them (with springs in place) you'll find the springs pull things into a square naturally. If you push it into a parallelogram, the springs will pull it back square. The weaker the springs, the less the effect. When your effector is beween towers the arms are in this parallelogram position, and the springs are fighting it. Something has to give. It flexes the outer arm - the longer your arms are, the more they flex, and it pulled up on that corner of your effector.
The effect actually is very repeatable and measurable.
If you build one of the effector tilt measurement probes I made, you can observe this effect in real time, and how much it tilts the effector on your delta. Info on that here: https://www.duet3d.com/forum/thread.php?id=1306
That said, the springs are NOT the cause of this issue, they just muddy it up and amplify it some. I'm running magball arms which don't need linkages or springs, and still see the "taco bowl" shape to my probe output.
Here's a brief list of things I've tried to diagnose this:
Seemecnc stock effector, 713Maker aluminum effector, custom aluminum magball effector
Seemecnc 292mm stock ball cup arms, Trick Laser 300mm CF ball cup arms, Haydn Magball arms (304mm)
Seemecnc Accelerometer probe, dc42 IR probe, Piezo Probe
Seemecnc injection molded carriages, Trick laser aluminum carriages (current version)And then I've also made the electronic tilt measurement, so I could measure and eliminate tilt in my effector to rule that out. (I have no measurable tilt at this point, either digitally with the accel/gryo, or with a bubble level).
I have loads of spreadsheets of data gathered, but have yet to find anything other than increasing the arm length that gets rid of the "taco bowl" shape.
Big clarification on that last statement: Several of these have reduced the issue. Anything that adds tilt to your effector seems to really amplify the incorrect measurement of the arm length. The biggest improvement so far was going to magball instead of arms with springs between them)
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All, please bear in mind that I do not advise the use of 7 or 9 factor calibration. If you can't resolve the problem by using weaker springs or whatever, then I suggest you use mesh bed compensation to handle the residual deviation.
FWIW, my large Kossel with PCB effector and carriage adapters and Haydn's magnetic arms calibrates to a deviation of about 0.025mm using 8-factor calibration and AFAIR 13 probe points.
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Thanks for clarifying that, David. I should say I only use a 6 factor calibration for actual printing, and enable a mesh for larger prints. I'm mostly just interested in this from a "puzzle solving" perspective at this point. Though the majority of my time is now invested in my corexy project.
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So it appears that I got rid of my "ridges and valleys" problem.
I'm swapped carriage, effector, and arms to the following 325mm length ones from Trick Laser (I guess for a short while the 325mm length was in vogue):
http://www.tricklaser.com/300-MM-Carbon-Fiber-Tube-Arms-for-Rostock-MAX-RM-ARM-CFTX300.htm
The new arms narrow the "ridges and valley" problem down to either the arms being too short, the springs being too tight, or something associated with the movement of the newer ball joint arms.
I do have another pair of 300mm rods of the same style, so I will try those tomorrow to see if the results change or stay the same so we can remove or keep rod length as one of the contributing factors.
I'm running 6 point 140mm calibration with 6 midpoints all at the same H-0.10 FSR height. Deviation ranges from about 0.02 to 0.05, which seems to be good.
I did notice previously on the ball cup arms with springs, a ~0.05 deviation of layer height on very small circles (almost as if the springs were causing the effector to shift), so I may retry that calibration print on this setup and see if that was a symptom of the ball cup arms and springs as well.
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There's been speculation between a couple of us that long enough arms paired with either very weak or no springs would end the issue, so your results are interesting. There have been people with Traxxas ends who've reported the calibration oddity as well, but your follow up test with the 300mm arms will be good to see as well.
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There's been speculation between a couple of us that long enough arms paired with either very weak or no springs would end the issue, so your results are interesting. There have been people with Traxxas ends who've reported the calibration oddity as well, but your follow up test with the 300mm arms will be good to see as well.
I also specifically put the bands on the very, very end of the traxxis rods this time, nearly right on top of the joints around the plastic end pieces. That may minimize some of the warping of the carbon fiber rods. I might try with the bands in the very middle of the rods as well and see if I can maximize any warp effect from the carbon fiber rods.
I'll try to get the 300mm rods tested later tonight and post any visual results from printing the 0.2mm height large circle test.
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Also, I'm tempted to try 360mm magball Hadyn's arms from Ultibots.
Any downside to having vastly longer arms like that? I would imagine the accuracy is slightly less for small movements, but I could perhaps offset that with 0.9 degree steppers.
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The longer arms give up a ton of Z, which sucks.
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Just posting some results for reference from a 22 point bed calibration, 325mm traxxis ball joint arms, and FSR sensor setup, using the past generation Trick Laser carriages, effector, and arms made for the Rostock Max v2 kit as upgrades.
Also, note how closely it calculates the correct delta radius (which is listed at 133mm).
[c]M561; clear any bed transform, otherwise homing may be at the wrong height
G31 X0 Y0; don't want any probe offset for this
M116 ; wait for all temps to reach set values
G28; home; 3 points at 140mm
G30 P0 X0.00 Y140.00 Z-99999 H-0.05
G30 P1 X121.24 Y-70.00 Z-99999 H-0.05
G30 P2 X-121.24 Y-70.00 Z-99999 H-0.05; 3 points at 130mm
G30 P3 X0.00 Y130.00 Z-99999 H-0.05
G30 P4 X112.58 Y-65.00 Z-99999 H-0.05
G30 P5 X-112.58 Y-65.00 Z-99999 H-0.05; 3 points at 120mm
G30 P6 X0.00 Y120.00 Z-99999 H-0.05
G30 P7 X103.92 Y-60.00 Z-99999 H-0.05
G30 P8 X-103.92 Y-60.00 Z-99999 H-0.05; 6 points at 75mm
G30 P9 X0.00 Y75.00 Z-99999 H-0.05
G30 P10 X64.95 Y37.50 Z-99999 H-0.05
G30 P11 X64.95 Y-37.50 Z-99999 H-0.05
G30 P12 X0.00 Y-75.00 Z-99999 H-0.05
G30 P13 X-64.95 Y-37.50 Z-99999 H-0.05
G30 P14 X-64.95 Y37.50 Z-99999 H-0.05; 6 points at 50mm
G30 P15 X0.00 Y50.00 Z-99999 H-0.05
G30 P16 X43.30 Y25.00 Z-99999 H-0.05
G30 P17 X43.30 Y-25.00 Z-99999 H-0.05
G30 P18 X0.00 Y-50.00 Z-99999 H-0.05
G30 P19 X-43.30 Y-25.00 Z-99999 H-0.05
G30 P20 X-43.30 Y25.00 Z-99999 H-0.05G30 P21 X0 Y0 Z-99999 H-0.05 S6
M500; Save print settings to config-override
[/c]Calibration console output:
[c]Calibrated 6 factors using 22 points, deviation before 1.810 after 0.019[/c]
And then the new config output is here:
[c]; This is a system-generated file - do not edit
; Delta parameters
M665 L325.000 R132.978 H332.047 B140.0 X-0.012 Y0.268 Z0.000
M666 X-0.491 Y0.820 Z-0.330 A0.00 B0.00[/c] -
The longer arms give up a ton of Z, which sucks.
So get longer verticals.
Deltas have massive Z dimension which I am sure almost no one ever uses.
