Arm length calculation help on own-design delta needed August 02, 2014 05:31PM |
Registered: 10 years ago Posts: 20 |
Re: Arm length calculation help on own-design delta needed August 03, 2014 09:05AM |
Registered: 11 years ago Posts: 732 |
Re: Arm length calculation help on own-design delta needed August 03, 2014 02:57PM |
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Re: Arm length calculation help on own-design delta needed August 03, 2014 04:32PM |
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Re: Arm length calculation help on own-design delta needed August 03, 2014 05:33PM |
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Re: Arm length calculation help on own-design delta needed August 06, 2014 05:06AM |
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Re: Arm length calculation help on own-design delta needed August 06, 2014 02:59PM |
Registered: 11 years ago Posts: 732 |
If you mean angle between a diagonal rod and the corresponding tower when effector is at position (x,y)=(0,0) then it is typically 30° but can be more or less. This number is not that important and has nothing to do with SIN_60/COS_60 in firmware.Quote
allempty
I built a delta earlier this year and found that the most important point is to make sure the angle of the push rods from the ball joint centres is exactly 60 degrees to the vertical slides.
Of course it did not help. The SIN_60/COS_60 constants in firmware are related to computation of virtual tower positions and not to diagonal rod. They do not have anything to do with diagonal rods at all.Quote
allempty
Using Marlin as control sw :- got the angle wrong on my first attempt (58.62 degrees), I modified the angle value in config.h expecting the calculations to then be corrected.
This approach did NOT work so after very careful measurements, recalculated and extended my rod lengths to correct the angle to 60 degrees.
Not really. You can round SIN_60/COS_60 to about 4 decimal places after dot and there will not be a noticeable difference.Quote
allempty
// Effective X/Y positions of the three vertical towers.
#define SIN_60 0.8660254037844386 // 0.8660254037844386
#define COS_60 0.5 // 0.5
These are for my machine it will not be correct for you, notice the number of decimal places for SIN 60 !!! rounding errors will cause problems.
No. You are just printing your parts distorted by about 0.15 mm. (That is provided your bed is planar.)Quote
allempty
I have errors in the Z plane when the head moves, the bed appears to be dished but with in 0.15 mm, a sort of doughnut shape ,but after the first layer is layed down the errors are compensated for.
Re: Arm length calculation help on own-design delta needed August 07, 2014 04:27AM |
Registered: 10 years ago Posts: 20 |
Re: Arm length calculation help on own-design delta needed August 07, 2014 05:59PM |
Registered: 10 years ago Posts: 240 |
Re: Arm length calculation help on own-design delta needed August 07, 2014 06:50PM |
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Re: Arm length calculation help on own-design delta needed August 08, 2014 04:30PM |
Registered: 11 years ago Posts: 732 |
I'm not sure this is true. At the location most far away of a tower, the arm of that tower will have small angle to bed (in ybanrab situation about 24° which is not that small anyway). But the arms to the other too towers will have quite big angle to the bed (about 63°), those arms should take the most of the probing force (which is in the Z axe direction). Maybe this situation may be bad when the pairs of arms going to the same tower are too near to each other, but hopefully all people realize that the distance between arm pair should be as big as possible (within the design constrains of the effector platform).Quote
sheepdog43
Also, if you plan to auto level or auto calibrate, just reaching the edge of the build plate is not enough. The further out you go, the more flat one arm will be, leaving you little to no leverage to depress the probe. Even if you do have a little extra, I recommended not probing more than 75-80% from the center of the build platform to reduce wear and tear as it is VERY hard on your diagonals doing this.
I do not understand why bigger printer would need bigger accuracy of parts barring the problems of frame/rod elasticity (probably what you mean by deflection). Lets say that the bigger printer used stronger rods/towers etc. so that it does not flex. Then lets assume the printer is perfectly precise. Now imagine that you change one printer part to be imprecise. E.g. a tower position by 0.1 mm. This 0.1 mm imprecision will not lead to bigger imprecision than 0.1 mm in the effector location (regardless of the printer size). So what you are saying does not make sense to me maybe only if by precision you are talking e.g. about angle precision and not distance precision. Small angle error may lead to big position errors at the end of angle arm if the arm is long.Quote
sheepdog43
As you go out, and increase leverage, you also increase deflection, on larger printers, this can be a big problem. I usually probe at 70-80% on my smaller printer, but only 60-70% on my big printer to decrease the deflection. I use the same accuracy level, however, because as you go up in size, the same accuracy requires more and more precision. 0.03mm accuracy on a Kossel Mini may require your radius to be accurate to .01, but on a 500mm bed, to reach 0.03 accuracy across the bed may require an accuracy of 0.001 or even 0.0001. Because of this, iIt can take far longer to calibrate larger printers. Sometimes multiple runs, getting more and more precise.
Re: Arm length calculation help on own-design delta needed August 08, 2014 04:45PM |
Registered: 11 years ago Posts: 732 |
Re: Arm length calculation help on own-design delta needed October 12, 2014 05:36PM |
Registered: 10 years ago Posts: 25 |
Re: Arm length calculation help on own-design delta needed October 12, 2014 05:50PM |
Registered: 10 years ago Posts: 20 |
Re: Arm length calculation help on own-design delta needed October 12, 2014 06:07PM |
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Re: Arm length calculation help on own-design delta needed October 12, 2014 08:47PM |
Registered: 10 years ago Posts: 240 |
Re: Arm length calculation help on own-design delta needed October 12, 2014 09:25PM |
Registered: 10 years ago Posts: 240 |
Quote
hercek
I'm not sure this is true. At the location most far away of a tower, the arm of that tower will have small angle to bed (in ybanrab situation about 24° which is not that small anyway). But the arms to the other too towers will have quite big angle to the bed (about 63°), those arms should take the most of the probing force (which is in the Z axe direction). Maybe this situation may be bad when the pairs of arms going to the same tower are too near to each other, but hopefully all people realize that the distance between arm pair should be as big as possible (within the design constrains of the effector platform).Quote
sheepdog43
Also, if you plan to auto level or auto calibrate, just reaching the edge of the build plate is not enough. The further out you go, the more flat one arm will be, leaving you little to no leverage to depress the probe. Even if you do have a little extra, I recommended not probing more than 75-80% from the center of the build platform to reduce wear and tear as it is VERY hard on your diagonals doing this.
An original rostock here does not have problems probing about 80% away from centre.
When you calibrated your printer, remember how the print was bowl shaped? It's not linear, the further out you go, the worse the bowl shape gets.Quote
hercek
I do not understand why bigger printer would need bigger accuracy of parts barring the problems of frame/rod elasticity (probably what you mean by deflection).
Re: Arm length calculation help on own-design delta needed October 13, 2014 01:03AM |
Registered: 10 years ago Posts: 25 |
Re: Arm length calculation help on own-design delta needed October 13, 2014 05:33AM |
Registered: 11 years ago Posts: 732 |
The angles change with changing printer delta radius and diagonal rod length.Quote
plastik
What angle should the rods have when the nozzle is all the way to the edge of the printing bed? Is it 20 degrees?
Re: Arm length calculation help on own-design delta needed October 13, 2014 06:25AM |
Registered: 11 years ago Posts: 732 |
In such a position, the horizontal pair does not need to prevent rotation in the horizontal axe perpendicular to it (other two arm pairs will do it just fine). The horizontal pair still needs to prevent rotation along vertical axe (which would lead to smaller platform tilting too). Maybe you are right and these positions are significantly worse even when arm pair distance is big enough but I have doubts without proper momentum propagation analyses.Quote
sheepdog43
Quote
hercek
I'm not sure this is true. At the location most far away of a tower, the arm of that tower will have small angle to bed (in ybanrab situation about 24° which is not that small anyway). But the arms to the other too towers will have quite big angle to the bed (about 63°), those arms should take the most of the probing force (which is in the Z axe direction). Maybe this situation may be bad when the pairs of arms going to the same tower are too near to each other, but hopefully all people realize that the distance between arm pair should be as big as possible (within the design constrains of the effector platform).Quote
sheepdog43
Also, if you plan to auto level or auto calibrate, just reaching the edge of the build plate is not enough. The further out you go, the more flat one arm will be, leaving you little to no leverage to depress the probe. Even if you do have a little extra, I recommended not probing more than 75-80% from the center of the build platform to reduce wear and tear as it is VERY hard on your diagonals doing this.
An original rostock here does not have problems probing about 80% away from centre.
All three sets of arms are needed to hold an effector in place horizontally. If one set of arms is horizontal, they are no longer holding the effector flat and the effector can rock. It doesn't take much to throw off calibration. Yes, two sets are holding it down, but we have three sets for a reason. Take off a set of arms and you will see where the problem is.
Here we claim essentially the same thing. Non linearity causes the errors to be bigger at the heat bed edges. But we are looking at it from different angles:Quote
sheepdog43
When you calibrated your printer, remember how the print was bowl shaped? It's not linear, the further out you go, the worse the bowl shape gets.Quote
hercek
I do not understand why bigger printer would need bigger accuracy of parts barring the problems of frame/rod elasticity (probably what you mean by deflection).
So lets say your Kossel diagonal is accurate to within 0.04mm giving you great precision. However, in reality, you probably aren't perfectly flat. There can still be 0.01mm bowl shape in your print, you just can't spot it and it's irrelevant.
That 0.01mm bowl shape at 170mm wide balloons up to 10mm by the time you reach 500mm wide. You need to dial down to something like .0015 diagonal accuracy just to get a .01mm accuracy across the bed at 500mm.
Re: Arm length calculation help on own-design delta needed October 13, 2014 05:49PM |
Registered: 10 years ago Posts: 25 |
Re: Arm length calculation help on own-design delta needed October 14, 2014 07:31AM |
Registered: 10 years ago Posts: 240 |
Quote
hercek
In such a position, the horizontal pair does not need to prevent rotation in the horizontal axe perpendicular to it (other two arm pairs will do it just fine). The horizontal pair still needs to prevent rotation along vertical axe (which would lead to smaller platform tilting too). Maybe you are right and these positions are significantly worse even when arm pair distance is big enough but I have doubts without proper momentum propagation analyses.
You are right, it's good because you get a heck of a level build plane, I get fantastic prints from it, I hadn't really thought of that.Quote
sheepdog43
* you say this is bad because small calibration errors lead to big effector errors at bed edges;
* I say this is good because the small calibration errors can be detected at the edges (and thanks to that we can correct them).
Re: Arm length calculation help on own-design delta needed October 14, 2014 01:31PM |
Registered: 11 years ago Posts: 732 |
Quote
sheepdog43
The worst part though, was that you just lost 1/3rd of your load bearing pivots, and the other take all the abuse. After a few hundred iterations my ball joints were junk.
Re: Arm length calculation help on own-design delta needed February 19, 2015 06:42PM |
Registered: 10 years ago Posts: 14,684 |
Re: Arm length calculation help on own-design delta needed February 20, 2015 02:01PM |
Registered: 11 years ago Posts: 732 |
Quote
dc42
However, I'm wondering whether inaccuracies in the tower positions really are a more significant source of error than the towers being not perpendicular to the bed, or twisted, or the diagonal rods being slightly different lengths. Does anybody know?
Re: Arm length calculation help on own-design delta needed January 06, 2016 04:03AM |
Registered: 13 years ago Posts: 300 |
Re: Arm length calculation help on own-design delta needed January 06, 2016 04:32AM |
Registered: 10 years ago Posts: 14,684 |
Quote
fma
I'm wondering: does this design reduce the non-linearity, and so simplify the tuning?
[www.festo.com]
Re: Arm length calculation help on own-design delta needed January 06, 2016 04:50AM |
Registered: 13 years ago Posts: 300 |
Re: Arm length calculation help on own-design delta needed January 06, 2016 01:32PM |
Registered: 11 years ago Posts: 732 |
No. It does not help in any significant way compared to a simple linear delta. I would say it's complexity will be about the same but worst, I do not know about any prepared tools (like e.g. dc42 calibration web page or his firmware) which would help you.Quote
fma
I'm wondering: does this design reduce the non-linearity, and so simplify the tuning?
[www.festo.com]
Re: Arm length calculation help on own-design delta needed January 06, 2016 03:17PM |
Registered: 13 years ago Posts: 300 |