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Author Topic: distorted/cut off circles
polarhb
Newbie
Posts: 11
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Post distorted/cut off circles
on: June 19, 2013, 18:23
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My polargraph is roughly functioning.

Here are the initial images I'm getting drawing a circle.
Image

The object below is the SVG circle attached.
Image

As you can see the resulting image is distorted and has the left and bottom "cut off". This homemade drawbot is running off of spectra line similar to the makeangelo http://www.marginallyclever.com/shop/index.php?main_page=product_info&cPath=1&products_id=39.
using an arduino mega running the most recent version of polargraphcontroller and polargraph_mega code. I'm using eyebolts to run the strings over the corners. Movement seems visually smooth.

both motors appear functioning although there is a lot of hesitation/pausing while printing. the properties file I'm using is at http://bit.ly/17Yo38v

I suspect(ed) some assymmetry between motor movement; I've switch motor driver chips in the arduino motor shield. Note the left and right sides appear different.

The cut-off areas are puzzling - the pen just skips over those areas then jumps to the point where the "circle" would being.

Any guidance or thought on how to fix this? I could adjust pixel scaling but I don't understand why I would need to.

-hb
sandy
Administrator
Posts: 1317
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sandy
Post Re: distorted/cut off circles
on: June 19, 2013, 20:09
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Yes that's a peculiar one hb. It looks like the page size has been reduced so that the bottom and left edge have been cut off, but loading your files, the circle is intact. And you woulda noticed it too.

I assume this is drawing the same circle, twice, once small, once scaled up a bit?

The small one looks ok (well, ish), the big one looks cut off. Either way there's a miscalibration that leads to the distortion. How is the dimension? I expect that circle to be around 170mm wide. Are you definitely using 400-step motors? (I only ask because most are 200 step.)

Does the machine report any errors while doing the skipping? (ctrl-c to show the console in the controller - the raw communication between the controller and the machine.) The only thing that springs to mind is that the machine might have it's size set incorrectly - so it thinks the circle will take the pen off the side of the surface.

A way to test is by doing a "move pen to point" and "move direct". Standard move pen to point does not care about whether the pen is off the surface or vertical, or anywhere. "Move direct" _does_ respect the set boundaries of the surface, and can be used to map the extent of the machine.

I assume you have uploaded your machine spec.

Oh and let us have a closer look at that gondola? 🙂

sn
polarhb
Newbie
Posts: 11
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Post Re: distorted/cut off circles
on: June 20, 2013, 08:58
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ok, I think there were three errors, now all fixed.

The first is that I hadn't in fact 'uploaded my machine spec' after calculating and changing the parameters. That fixed the cut-off circles.

The second was a 1/4" misalignment of the eye hooks holding the string. This contributed to both a distance error between the eye hooks and a vertical displacement. Although a 1/4" doesn't seem a like a lot, the math must highly exaggerate this effect resulting in the highly distorted circles.

Once my 'circles' were bilaterally symmetric, I found that I misunderstood how the home page y was set up. Once I resolved that, I started getting nice circles!

thanks Sandy, looking forward to use my drawbot!

by the way, the gondola is a 3d printed one: http://www.thingiverse.com/thing:28854

--polarhb (rrhb)
sandy
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Posts: 1317
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sandy
Post Re: distorted/cut off circles
on: June 20, 2013, 10:37
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Aha I thought I recognised the front edge 🙂 Glad you got things sorted out!

sn
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