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Author Topic: printing large scale - skew (?)
etaifour
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Post printing large scale - skew (?)
on: January 2, 2013, 14:18
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Happy new year all!

I've been playing with DRBO for few weeks now (Thanks Stuart and Sandy for everything!), but wasn't satisfied anymore with small print areas 🙂
I'm trying to experiment printing on larger cardboard (1 meter * 70 cm), installed on a chassis right on top of the DRBO. I've added 4 screws on the corners as instructed here: http://stuartchilds.com/2012/07/drbo-experiments-and-drawing-big/

I've entered the machine size, paper size, made sure the homepoint is 120mm away from the upper edge. When I print, I get some strange effects:
- Clicking interactively in Polygraph, I can't get to the edge (my gondola doesn't make it there).
- If i try to print a simple box, the result is "skewed" (the edge on the bottom, nearest to DRBO, is half the size of the upper length).. i dont understand this distortion
- the length of my box is 80% smaller than what I'd like it to be.

I wonder what configuration I should make. Do i need to go into revs, speed, acceleration, or any of that sort? should i try placing my "chassis" anywhere else?

I'd appreciate your help!
Thanks!
Eyas
sandy
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sandy
Post Re: printing large scale - skew (?)
on: January 2, 2013, 16:33
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Hello! Happy new year to you too 🙂
Have you uploaded the new machine specification to the arduino? The location of the DRBO itself won't make any difference. Only thing you should need to change is the machine size in the controller, and then do "upload machine spec" to make sure the machine itself also knows the size.

sandy
etaifour
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Post Re: printing large scale - skew (?)
on: January 2, 2013, 20:59
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Yes, I made sure to enter the settings correctly and do "upload machine spec".. I can't explain the transformation. I keep on playing with "move direct" to make sure the pen on the screen is where it is supposed to be in reality, but the destination is unpredictable.
sandy
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sandy
Post Re: printing large scale - skew (?)
on: January 2, 2013, 23:13
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When you say the gondola doesn't make it to the edge when you drive it interactively - do you mean clicking on the edge of the machine (on screen) makes the gondola drives to a different place on the surface? Is it reproducible? That is, when you click in four distinct places on the screen, does the machine draw to the same four different points on the surface?

You could try a "download machine spec" to make sure that the machine has got the message. Does the machine have any problem with holding at the home point? Or getting back to it? In fact that's a good thing to try - draw to a point somewhere down the surface, then make it draw back to the home point.

That kind of shape where the top is big and the bottom is small means that the machine is drawing higher than it thinks it is - or also the machine is physically wider than it thinks it is.

You might try opening the console using "c" and then doing your "upload machine spec" and see if there's any funny messages get repeated back.

sn
etaifour
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Post Re: printing large scale - skew (?)
on: January 3, 2013, 09:57
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Thanks! My latest machine now is 961mm x 750 mm. (no errors in polargraphcontroller).
if I close the app, re-open it, select serial port, and download size specs, I get indeed something a lot bigger (3684 x 2872). This seems to be corrected when I change the motor max speed to 100 and accel to 50. in my case, it seems I always have to adjust the motor max speed and acceleration settings, even if i load a config that was previously saved.

I'm using 91mm per rev, 200 steps per rev, 1 step multiplier.
i'm not really sure how to proceed further - how can i open a console using C?
sandy
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sandy
Post Re: printing large scale - skew (?)
on: January 4, 2013, 12:17
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Hi you can open the console just by pressing "c" anywhere in the controller - it pops up a little window that lets you see the raw communication between the machine and the controller - sometimes gives a few more clues as to what is going on.

For anything based on an arduino UNO+ adafruit motorshield, the steps per rev should be doubled - so you should be entering 400 steps per rev (the other two values are right). That on it's own will make somethings a bit weirdly shaped / scaled, but it sounds like the upload isn't working either. Looking at the console during the upload might shed some light on that.

When you say that changing the speed and acceleration corrects the size of the machine, do you mean it corrects it in the controller - the machine changes size when you issue a change speed command?

One thing to note is that you're often better off changing the steps per rev and things like that by editing the default.properties.txt file manually rather than using the controller for it. The controller sometimes tries to be a little too clever (ie stupid) and ends up making things harder.

sn
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