How do I use Delta Correction?

FelixP

Hi, so I'm trying to use the DELTA_RADIUS_CORRECTION and DELTA_DIAGONAL_CORRECTION variables in order to correct build errors in my printer and improve the calibration. However, I'm not really sure if I'm using these variables correctly. I haven't been able to find any instructions out there on how to use these variables.

Here's the issue with my printer: When printing a calibration object, such as this one: http://www.thingiverse.com/thing:745523</div><div>the lengths of the legs on the print are incorrect. When calibrated correctly, each pair of parallel legs on the snowflake should measure 120 mm on each side. Instead I get lengths like 119.53 (across tower A) 120.95 (across tower B) and 120.11 (across tower C). The instructions are written for the Marlin firmware, and the author has no interest in providing a Repetier version.

I know I'm not the only one with this problem, but I just cannot find a clear explanation. All the printer guides I find don't address this part of calibration.

Repetier

Ok I have read the instructions and adaption is quite simple - even easier then in Marlin:-)

In EEPROM you see the 3 delta tower angles which are normally 120° apart. Simply change these values like you would change the degrees in Marlin code. So if tower C should not be at 90° but 90.3° just enter 90.3 in that field, thats it.

Do not attach radius correction. What he describes are the Corr. diagonal A/B/C values in EEPROM. Here you do not enter a factor like he computes but the difference between his target diagonal length and the one you have set.

FelixP

Ok, so for example, with the 120.95, I put -.95 into the tower B radius correction? is that right?

Repetier

No, he and I were talking about diagonal correction, so put it there. So if original diagonal is 200 according to his formula new diagonal would be

200 * 120.95 / 120 = 201.58

So you enter Coor diagonal A 1.58 to close the gap to 200 which you had set already.

BarryLaw

My Corr. diagonal A(0) shows 0.000 B&C have the same value. Should I just put the amount of the error in there or should I still do like what you have above?

FelixP

I'm not sure if I've read your suggestion correctly. Currently, the angles are very close to 120 degrees, but the lengths of the legs on the object are not.

The length of the leg closest to Tower B and the leg colinear with that leg measure the length of 121 mm exactly, while the other legs are 120 mm. What am I supposed to calculate, and where do I put the results in EEPROM? (I have repetier host as well)

Repetier

Put in Corr diagonal A/B/C (depending on your error) diagonal*121/120 - diagonal

Also that is only a first approximation, but that is what the instructions say translated to repetier.

FelixP

Okay. Here's what I got:

when side A is 120 mm long, side B is 120.08 mm long and side C is 120.88 mm long, I calculated:

( 120.88 / 120 ) * 392.35 = 395.227

395.227 - 392.35 = 2.877

(392.35 is my diagonal rod length)

So I put 2.877 into Corr. diagonal B and 0.261 into Corr. diagonal C and I ended up getting 120.45 for the length of the B legs and 119.20 or so for the other legs. Am I supposed to decrease the diagonal rod length again until one of the legs measure 120 mm again and then subtract the difference again, then repeat the process? Or did I do something wrong here?

Repetier

Why did you put the correction for c which you computed in B and vice versa?

FelixP

I mistyped that. I meant to say side B is 120.88 mm long and side C is 120.08 mm long.

FelixP

ACK! I actually put them in the wrong spots, give me a minute to see what happens when I swap them around.

FelixP

I applied the corrections, and now all the endstop positions are out of whack. is this supposed to happen?

Repetier

Diagonal correction ha sno influnence on endstops. But it might change where z=0 is.

FelixP

ok, but my settings for the endstops are no longer valid, by quite a lot. the carriage on tower b will now drop a significant amount when homing, and the offsets put in the firmware for the endstops are no longer valid.

Is this supposed to be happening? Am I supposed to re-measure the endstop offsets for this new value?

Repetier

I didn't do it so I can only guessed that something went wrong while changing your values. Maybe wrong field ...

Since you say they are wrong, yes you have to recalibrate them.

paweueu

Hi,

I can't set up my printer - the problem is with print size. I tried to print the above linked "caldelta" circle few times. Every time I have wrong dimensions. This is how I am calculating:

My print size is:
X = 59.9 (reference)
Y= 60.27
Z=59.8

New diagonal len.:
Old * (59.9/expected = new Diagonal len.
213.993 * 59.9 / 60) = new Diagonal len.
new Diagonal len = 213.565

Corrections:

Tower A = no correction as (59.9 has the lowest error and it is already corrected by new diagonal Len)
Tower B = 60.27 - 59.9 = 0.37 (+60mm which is the desired dimension)
Tower C = 59.80 - 59.9 = - 0.1 (+60mm which is the desired dimension)

now I count new diagonal len for tower B and C:

Len B = new diagonal len * ( Tower B / 60) = 213.565 * (60.37 /60) = 213.565 * 1.006 = 214.84
Len C = new diagonal len * ( Tower C / 60) = 213.565 * ( 59.90 /60) = 213.565 * 0.998 = 213.12

Corrections:

Corr B = 214.84 - 213.565 = 1.275mm
Corr C = 213.12 - 213.565 = -0.445mm

So I put this 3 values to EEPROM:

Diagonal rod length, Corr. diagonal B, Corr. diagonal C.

Do you think my calculations are ok?
Every time I use newly calculated numbers I receive bad print size...

Regards
Pawel

Roko

<font face="Arial, Verdana">I used the link :http://www.thingiverse.com/thing:745523 to check/setup my angles.</font>

<font face="Arial, Verdana">then I used this from Thingiverse.</font>

<font face="Arial, Verdana">https://www.thingiverse.com/thing:1274733 for the diag sizing.</font>

<font face="Arial, Verdana">It took me about 7 iterations of the 2nd link before I was satisfied with the result. but it worked for me.</font>

paweueu

Thanks Roko, will try with this solution

paweueu

I tried your way, but I am not sure.

I entered my values like below

Horiz. Radius 107 (I am not sure if this value is correct)
D0 - current diagonal 213,84
L (suposed measure) 75
Lx 75.39
Ly 75.04
Lz 74.75

Output for Repetier is:
Diagonal rod len 213.901
Corr diagonal A 0.346
Corr diagonal B -0.019
Corr diagonal C -0.32

Ok. Printed again and my dimensions are still wrong,

Z=74.86
Y=74.6
X=74.76

You did 7 iterations. But how - should I change those 4 parameters again and again?

Roko

Yes I entered the new values into the spreadsheet.