I'm still just starting to draw with the new build and working out a lot of issues. On my larger prints, the top is a lot more consistent than the bottom. As the pen moves further down the board, it gets a bit of an oscillation as it draws resulting in loopy waves. Maybe its my gondola design, but thought I'd kick it out here to see if someone else knows where to start isolating the problem

Thanks!

Josh

Without seeing the lines themselves, I'd say that was pretty normal. The longer the cords are, the more acute the angle between the two lines is, and the less stable the gondola is. Keeping the drawing accurate at the lower levels is one of the main challenges. The solution, in my experience, is to bring the point at which the gondola hangs from the string closer to the surface. That is, make the pen not stick out as far. So there's a more direct connection between the movement of the cords and the movement of the pen tip.

The big circular stabiliser was kind of a minor solution to that, but adding extra weight to the gondola also helps a lot to keep everything a wee bit more taut.

sn

Aha, well, a proper polargraph (brand!) gondola has a double attachment, but each attachment pivots independently. The theory is that the string coming off it will _always_ intersect the central axis of the pen, so the pen will always be at the point of the triangle.

A (above) is the most common, but has the problem that when the gondola is up high, then the true point of intersection will be _above_ the actual pen. When the gondola is low, then the true point of intersection will be below the actual pen. Only at a small sweet spot will the intersection coincide with the actual pen.

B is in many ways the better design because you know that the pen tip will always be a fixed distance below the true intersection of the lines - it'll be geometrically simple. The downside is that it means that the pivot point of the pen itself is dangerously unstable. When the intersection moves sideways, the gondola will get dragged behind the real point, and might not catch up.

If I'm honest, the decisions I made when making up the first polargraph gondolas, were made to try and squeeze the hard-to-model aspects out of the design, so I could be more sure that moving the string x number of steps would result in a line on the page x number of steps long. In practice, I don't know if these problems with A or B above really make much difference. I mean, I know there'll be a slight distortion at the limits of the A gondolas reach, and B will struggle to get to the corners of lines, without a heavy weight and a low speed, but will either result in unforgivable problems? Maybe not, but as far as I'm concerned, it's one less variable to worry about.

sn