Forum

Welcome Guest 

Show/Hide Header

Welcome Guest, posting in this forum requires registration.





Pages: [1]
Author Topic: Asymmetrical drawing / drawing area too big.
simon
Newbie
Posts: 8
Permalink
Post Asymmetrical drawing / drawing area too big.
on: November 29, 2017, 16:50
Quote

hi there,

I am using a polargraph v2 and I have some problems with asymmetrical drawings. (I've already checked my machine specs 10 times and remeasured... and everything seems to be adjusted correctly. > I read the posts about bad homing and other forum-posting but I didn't find the solution.)

I have a sagging line at the top of the page and the gondola always moves beyond the bottom edge of my paper.
however, when I move the gondola 2cm up, the sagging line gets better, but my drawings keep getting distorted, with the left side (lines from top to bottom) being not straight and veering off to the right.

So I wonder, what could be the issue? Any help is greatly appreciated. (Otherwise the polargraph is a wonderful piece of equipment, btw.)

Simon

sandy
Administrator
Posts: 1254
Permalink
sandy
Post Re: Asymmetrical drawing / drawing area too big.
on: November 30, 2017, 20:45
Quote

Hi! It'd be good to see your properties file and a pic of the drawings it makes.

Obvious stuff:
1) measure properly (https://youtu.be/wI8Bf8yubeA?t=3m22s)
2) upload machine spec
3) measure and mark home point just as properly
4) always "set home"

It sounds like your machine has the wrong settings loaded, and in particular the wrong width, or the home point isn't where you think it is horizontally. That'll lead to the asymmetry.

So perhaps the "upload machine spec" hasn't worked, you didn't mention it. Pop open the console (ctrl+c) and then resend "upload machine spec" and make sure there are no error messages being passed back from the machine.

Good luck,

sn

simon
Newbie
Posts: 8
Permalink
Post Re: Asymmetrical drawing / drawing area too big.
on: December 6, 2017, 15:59
Quote

hey sandy,
thank you for your quick response!
I tried again and made sure that I follow every step you mentioned above.
but again, the drawing gets distorted. the machine still thinks that the paper is 2 cm larger at the bottom, then it actually is. also no errors in the console, when I uploaded machine specs. also the top line gets really whobbly, which is not the case with the other lines...
when I tried to draw a simple rectangle inside the the edges of the paper, I got following result. those are my properties.

thanks for helping! 🙂

# *** Polargraph properties file ***
#Wed Dec 06 16:00:02 CET 2017
controller.pixel.samplearea=1
controller.pictureframe.position.y=136
controller.pictureframe.position.x=57
controller.testPenWidth.startSize=0.5
controller.machine.colour=969696
machine.motors.mmPerRev=95.0
controller.window.width=1243
controller.frame.colour=C80000
controller.image.position.y=167
controller.image.position.x=378
machine.motors.accel=700
controller.image.height=285
controller.machine.serialport=3
controller.window.height=653
controller.maxSegmentLength=2
controller.geomerative.polygonizerLength=1
machine.penlift.up=148
machine.penlift.down=60
controller.page.position.y=120
controller.vector.scaling=121.6
controller.page.position.x=100
controller.pictureframe.width=774
machine.step.multiplier=8
controller.grid.size=7.0
controller.testPenWidth.endSize=2
controller.pictureframe.height=1052
controller.page.colour=DCDCDC
controller.testPenWidth.incrementSize=0.5
controller.image.width=428
machine.motors.stepsPerRev=200.0
machine.pen.size=1
controller.page.width=700
controller.pixel.mask.color=00FF00
controller.machine.baudrate=57600
controller.vector.minLineLength=0
machine.width=920
controller.geomerative.polygonizer=0
controller.page.height=1000
controller.vector.position.y=152.22
controller.background.colour=646464
controller.image.filename=
controller.vector.position.x=87.37
controller.homepoint.y=120
controller.guide.colour=FFFFFF
machine.motors.maxSpeed=600
controller.homepoint.x=460
controller.density.preview.style=6
controller.pixel.scaling=1
controller.densitypreview.colour=000000
machine.height=1500

Image

kongorilla
Pro
Posts: 341
Permalink
kongorilla
Post Re: Asymmetrical drawing / drawing area too big.
on: December 7, 2017, 21:28
Quote

On the one hand, historically, I'd say the measurements your machine is working with are wrong.

On the other hand, I've been on a long polargraphing hiatus because I was having the same problem. I worked hard and long on a super-deluxe polargraph rig, designed with precision in mind, and I couldn't get it to draw without the same distortion you're getting. (Either my distortion wasn't quite as bad as in your image, or I managed to get it better by fudging the numbers a bit). I went over the measurements countless times, and finally decided I needed a break.

Since other people haven't been complaining about this, and since my rig is a bit different, I'm hesitant to say there's something wrong code-wise. I've been assuming I've been blind to some mistake on my part. However, the image you posted is so familiar....

simon
Newbie
Posts: 8
Permalink
Post Re: Asymmetrical drawing / drawing area too big.
on: December 11, 2017, 09:26
Quote

Well, i asume that the mistake is only on my side 🙂 but i just don't know where to look anymore. I didn't go through the process of building it.myself, so i don't know a lot about the machine...

sandy
Administrator
Posts: 1254
Permalink
sandy
Post Re: Asymmetrical drawing / drawing area too big.
on: December 11, 2017, 10:43
Quote

Don't be so sure it's a mistake on your side. The code that's inside the Polargraph contains a very simple mathematical model of a machine and a hanging pen. "All models are wrong, but some of them are useful", and this model is ok most of the time, but it never exactly reflects the physical reality.

The attached pic shows the addressable space in the blue square. The model assumes that the cords always hang from the top corners of that addressable space, and so the top edge of the triangle formed by the hanging cords is always a) fixed width and b) fixed position.

Of course, it is _never_ actually in that position, though it approximates it a lot of the time. As the pen moves up the board, the actual hanging point rises above and away from the modelled point. This adds some creeping distortion towards the top of the drawing, where the plotted points are higher than they should be.

So I suppose the weird this is that your distortion is in the opposite direction... The pen is actually lower than the model thinks it is, not higher. I've been scratching my head over the weekend to think of a way to model or visualise this.

Image

simon
Newbie
Posts: 8
Permalink
Post Re: Asymmetrical drawing / drawing area too big.
on: December 11, 2017, 13:10
Quote

thank you so much for your thoughts and effort! I spent some more hours on the machine today and I still understand where the error is, but I found a solution so work with: homepoint (y) for the machine is now 140mm while in reality its 120mm. I also increased the margins towards the edges of the paper, so the drawing is more in the middle of the page. the distortions (understandabley) nearly disappear towards the center of the page and I have good results! (still a hack, but maybe some day I'll understand why/what/how)! big thanks anyhow!

Shorn
Newbie
Posts: 13
Permalink
Post Re: Asymmetrical drawing / drawing area too big.
on: December 13, 2017, 15:45
Quote

I have seen something similar with my rig if the machine is not level. It likes a little tilt front to back but not side to side. If it is not level, gravity will introduce an offset to the side as the gondola will always try to be in equilibrium with the gravity vector.

If you have a long carpenters level you can place it across the top of your stepper motors or a small one anywhere along the top as long it is on the same plane as the motors.

-Shorn

Pages: [1]
Mingle Forum by cartpauj
Version: 1.0.34 ; Page loaded in: 0.024 seconds.