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Initial Calibration

Posted by phild 
Initial Calibration
February 08, 2014 01:43PM

I'm currently building a mini Kossel. I have installed repetier firmware .91 and repetier host.

I don't have a hotend on the effector yet, I have a QTip extruding down grinning smiley Trying not to break anything while I learn this.

I'm entering G Codes in the manual control area just to get a feel for the device. Doing this I noticed that while moving from one side to the other at a constant Z, there is a significant 'peaking', maybe as much as 20 mm.

I had initially set my diagonal rod length to 215 which is the approximate length of the effector rods. Not finding anything else to adjust, I began to reduce this length (in the eprom) and retrying my horizontal move until I had (most of) the peaking out. However my diagonal rod length is now 105 and although the peaking seems to be gone, the coordinate system seems screwed up, for example to place the QTip on the edge of the 170mm glass plate in front of the X Tower, the coordinates are: X:-47.00 Y:-26.00 Z:4.00

What am I doing wrong?

What is the proper way to remove cupping or peaking?

open | download - eprom1.PNG (42.8 KB)
open | download - eprom2.PNG (15.2 KB)
Re: Initial Calibration
February 08, 2014 07:58PM
Did you try changing the horizontal radius setting? Check for any mechanical bindings in the effector plate rod linkages?

I'm at the exact same stage as you are with my self-designed Delta, and was having similar problems with the pencil getting higher as the effector moved away from the center at a constant Z. I don't have the end stops installed yet, so I am manually setting the carriages at the top using my ruler as a spacer/gauge on each post. This morning, I accidentally sent a "home" G-code...and all three carriages went *down* at the same time until the spring clips that I had holding the rods on popped off as the head crashed into the platform. No damage done thanks to the breakaway clips doing their job. but it made me realize that the motors were all running inverted since the motor direction test on a Delta is apparently to send a "home" command and ensure that they move *up* in parallel. Long story short, my pencil will now draw 20-40mm lines on a piece of paper after inverting all three motors in the config file with no other changes, whereas before it could barely go 10mm before the tip came off the paper. Just mentioning it in case you made the same mistake that I did..... confused smiley
Re: Initial Calibration
February 09, 2014 12:52PM

Thank you for the response.

Well, I've gone through the motors running the wrong way, the endstops on min instead of max.

Once those were corrected it behaves as I described in the first post. Everything seems to work as it should except for the peaking.

Re: Initial Calibration
February 10, 2014 02:35AM
There are 2 main factors influencing this. Diagonal rod length and horizontal radius. Diagonal rod size is very easy to measure. It is from rotation axis to rotation axis and should be set as known value as you can measure it to 0.5mm. So don't correct it more then measurement error and not 100mm. horizontal radius can be mesured when you put the effector exactly in bed center and measure the horizontal distance of the diagonal rod axis. Here it best computed from the plans you have for the printer. Or you put a height on a string on the higher axis and mesure horizontal distance until string.

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Re: Initial Calibration
February 10, 2014 07:16AM
How about the steps per mm settings on your stepper motors? If that is off, it could skew all of the triangle math.....
Re: Initial Calibration
February 10, 2014 08:09PM
Hi vreihen and repetier,

Thank you both for your responses. I think I have it.

I had the horizantal radius totally wrong, I'm not sure what I was using for this, the radius of the glass perhaps?

I know you mentioned this in your first post vreihen, but I'm totally on overload with this.

Best regards
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