resolution of the Z platform on the arc it describes

[realthor]

Hello,

I am wondering how is the variable resolution on the Z axis affecting the prints for rotary Z axis bots, like the Wally.

Let me explain a bit: moving the bed on the imaginary circumference of a circle, you get better resolution right at the top and bottom of the movement (+90, -90 degrees) and worse resolution when the bed is at the 0 and 180 degrees.

Because of this situation there is not a constant number of microsteps per layer height (say 0.1mm). If, for example, you set the dimensions and gear ratios /etc to obtain a resolution of 0.1mm at its worst position, then you will get a very fine resolution at the top and bottom but the resolution right next to that worst position is going to take fractions of a microstep to achieve the set layer height of 0.1mm.

If at the worst (0deg) you will get 0.1mm per microstep, next angles will get you less than 0.1mm for the subsequent microsteps as the resolution improves. Let's say the next angle can achieve a resolution of 0.09mm/microstep. In order to have a layer height at a constant 0.1mm, you would have to rotate the stepper with one step and then some more to compensate for the difference. But there is no way to divide a microstep even more.

I hope I was clear enough, maybe you guys, having thought of it more, understand it immediately. If more expl are needed, I can provide.

Thank you.

[realthor]

I think there's a bug in the view conut ... close to 2000 views and no answer... :-/

Anyway I asked the same thing on reprap forums cause I was pulling my hair out.
Anyone interested can follow this link:
http://forums.reprap.org/read.php?185,556558