Hiya,

I've hit a little problem. My polargraph has somehow gained a distortion. If you tell it to draw an A2 box 1cm smaller than the paper, it will be spot on at the bottom of the page but just off the edge of the paper at the top - i.e. the box is actually a trapezium that's about 12mm wider at the top than the bottom. I tried moving the motors further apart, increasing the weights, decreasing the weights, moving the paper down, re-uploading the machine spec etc, but to no avail. It seems to be much more noticable on A2 than A3. Anyone got any ideas what might be causing this?

Looking back at my earlier drawings this didn't appear to be happening.
This isn't a problem until you put a drawing in a frame when it really jumps out 🙁

Ta

Steve

Mis-homing is my first reaction too. It sounds like the cords are a little shorter than the machine thinks they are, so maybe your home point is physically a mite too high. Quick test can tell you if that's true or not though, so I guess you've probably already tried it.

Is the top line horizontal and straight?

There is nothing linear about this kind of machine, and as the angles from the spools change then so do the tangents of the cord and the effective width of the machine. The area in the middle is a lot more regular, but it isn't a big area. Could it be that you're drawing very close to the top edge of your machine (near your sprockets)? All the rules break down there, it's like the badlands of a polargraph machine - keep away from it.

This is a reason I don't draw rectangular borders around pics 🙂

Yes I think that's true to a point, but after a certain distance down the machine you start losing resolution at the edges (sides) too. There's a link on the front page to a good bit of plotter design theory that I was shown, and has a good diagram at the bottom and some discussion about what makes the sweet spot sweet.