Makelangelo – tuning it in
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I am running a custom build that produces great prints. But I do experience an issue that is mentioned in the trouble shooting link: https://www.marginallyclever.com/blog/2014/10/how-to-fix-9-common-polargraph-drawing-problems/
I have a slight “Pinching” that suggests my pen home position is too low on the board. When printing something that is square or rectangular in shape the bottom edge is wider than the top edge. When printing something circular, it comes out egg shaped.
So I raise the home position upward on the board but this doesn’t seem to change the outcome.
Has anyone experienced similar results that can list out steps taken to square up your prints?
What’s your pulley diameter?
True… I’m finding the outer diameter isn’t as important as the number of teeth.
20 tooth pulley moves 40mm per rotation.
The same pulley might have an outer diameter of 15mm, which is 47.12388980384690mm radius. Close.I’ll have to try diameter = 40mm / Pi = 12.73239544735163 and see what results look like.
What would be the setting for the ones you supply with the pulleys in the 3.2 kit.
Did you use the top bottom left right buttons to check the gondola is cantered? I use top and bottom first to check vertical centering, then I check left and right. Each Time if it’s off a bit I go home, move a little, and set home again. Then retest.
I should add the 40mm is because there are 20 teeth and it’s GT2 belt, or 2mm between each tooth. 20*2=40.
After carefully measuring and re-homing using top, bottom, left and right the bowing or pinching still occurs. What’s odd is that raising or lowering the home position doesn’t have an effect on the amount of pinching.
Here’s a photo showing the results after altering the home Y position 4 times.
Results…
– Print 001: HOME at the measured center point.
– Print 002: Home was set -5 from the original Print 001 home.
– Print 003: Home was set -15 from the original Print 001 home.
– Print 004: Home was set +20 from the original Print 001 home.Your sides look straight. Try increasing or decreasing your pulley diameter to stop the bowing. I would try 2 mm change in either direction and see which is better then home in on the perfect setting.
Is there a way to edit or remove a post. If not can you please remove the first of my two posts?
There’s a # in the top right corner of each post. Which one are you referring to?
What’s your machine width? You should measure from the bottom right corner of the left motor to the bottom left corner of the right motor, in millimeters.
#8427 deleted.
It occurs to me that you have built this machine yourself, and your motors are probably 200 step-per-turn. Makelangelos built by us are 400. You can adjust this in makelangelo-firmware. Probably get better results than tweaking the width.
Question on the above- if my stepper motors are 200 steps per turn, what do I change in the firmware to make this work? Is it this?
// calculate some numbers to help us find feed_rate
float pulleyDiameter = 4.0f/PI; // cm
float threadPerStep=0; // thread per stepI was a little confused about the input tuning dimensions, so I did this visual guide that might come in handy for others too. Dan, can you please confirm if the assumptions are correct?
I’m particularly interested in how the motor edge is mapped to where the belt leaves the pulley (i.e. the point where the belt’s length is calculated, I presume). For those of us making custom setups with multiple pulleys/spacers diverting the belt, the (yellow-marked) distances won’t be the same as in Makelangelo machines.
This I a great post. Thank you!
So… I have always treated the math as being from center of each motor shaft. That said, it is *not* the most accurate solution. It’s been merely “good enough”.
We know the spacers on the motor shafts are 6mm diameter and that the hole centers are 31mm apart (http://reprap.org/wiki/NEMA_17_Stepper_motor), so it should be possible to adjust for that. This gets extra fun when the pen holder is in the bottom corners and the belt stops touching the corner post. Whee….So… I fudged it close enough. If you have a better way to *very quickly* calculate a more accurate positioning then I am very interested in putting it the software.
You are most welcome, happy to help!
All I know is that the Kritzler code uses pythagoras formula to calculate the belt length, based on input dimensions going all the way to where the belt leaves the pulley. But not sure if that extra accuracy is visibly detectable in the drawings. As I read this and other forums, sometimes it seems a input dimension error of a few mm will mess up the entire image, and other times I get the impression it’s not that sensitive.
Maybe I’m overthinking this, but can you take a look at the below drawing and confirm my assumptions? I want to use a second pulley to move the belt away from the motor, before it bends and turns towards the drawing surface. Is my new imaginary measurement point correctly assumed?
I don’t get it.
both ends of the belt are going to the pen holder? that won’t work.
the loose end of the belt (with counterweight) is going to hand down and interfere with the end going to the pen holder? that will work, poorly.
As for the imaginary point… sure, that looks pretty close. I’d just calculate from the center. if you want to be really picky you could work out the point on the curve of the guide for every x,y position on the board, and then fine tune accordingly. it’s a difference of less than (circumference/4).
No, those are two different belt configurations shown at the same time. The right one (marked Makelangelo) is yours, and the left one (marked “mine”) is the one I have in mind. I should have clarified I’m using a cord and not a belt, kind of like this:
http://4.bp.blogspot.com/-22X2YVoGvbE/UlX3xNDssdI/AAAAAAAAvDk/CWg34sYm-mY/s1600/IMG_20130428_204618.jpgSo should I just define machine dimensions as where the outer pulley/pins are located? Or add a couple of mm X and Y to take into account the yellow-marked distance drawed in my first post from yesterday?
> So should I just define machine dimensions as where the outer pulley/pins are located?
yes. Then you can run a “border” test to see that it draws a nice rectangle with straight edges where you expect on the machine. that validates your settings and confirms where your drawing will appear.
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