Hello everybody,
my name is Luca and i am a college student.
I am working on a polargraph, i am using an arduino UNO and an adafruit motorshield v1.
I am using the latest version of polargraph on both firmware and controller (2017-11-01).
Everything is working fine except for my "pen lift" and "pen drop" mechanism. I am using a "kookye" mini servo. My problem is that the servo only goes clockwise instead of work both clockwise and counterclockwise.
I looked at the arduino code and the only values i've got are 90 for pen_down and 180 for pen_up.
I also tried to give 90 for pen_down and 270 for pen_up, but still nothing good.
Maybe someone can illuminate me why i have got so many problems with this mechanism.
Thanks, Luca

That's a good question - Luca, do you mean it just goes round and round the whole time? Or do you mean it only ever goes the correct distance in one direction? So I mean it moves 90 degrees clockwise, but you've got to turn it back counter-clockwise with your finger?

Have you tested the motor with a non-polargraph sketch? There's one called "sweep" in the standard Arduino examples.

sn

So how do you get it back to the start position once it's moved?

What's confusing you about the 90/180 degree setting for the servo? One is "pen up", the other is turned 90 degrees and "pen down". It's in the middle of the range of motion because the ends of the range tend to be a bit "twitchy" and non-linear.

Remember you can change the parameters on the "setup" tab of the controller -
"pen up position", "pen down position" will change those up and down positions. "Test lift range" does a few strokes through the range, and "upload lift range" writes the new range to the arduino - it replaces the 90/180 that you see in the code.

sn

I cannot return it to the start position because my servo is keep adding 90 +180 everytime a pen_up or pen_down is call.
For me is confusing 90/180 because i imagine that the movement should be 0/90.
If i set 90/270 the servo doesn't act correctly and tries to go counterclocwise.

Hello again everybody, i have good news.
I discover a tiny potenziometer on my servo, i turned it and my motor started going clockwise and counterclockwise!
now i've another problem because my servo rotate fine but it's jittering so it never return to the exact position. How can i adjust it ? do i need do change some variables in the arduino IDE ?