Custom Polargraph misc questions

[Amin]

Hi Dan,

First off, thanks for having put together all these amazing robots and sharing them!
I’m building a custom Polargraph that I will later turn into a Zarplotter. I’m using spools and cord, instead of pulleys and timing belt (wanna see if I can make it work).

I just started and have put together my Arduino Mega + Ramps + A4988’s, and uploaded your firmware without errors. Starting with a single stepper motor (1.8deg/step) connected to Ramps’s X output, I am getting what looks to be the expected motion when using the Makelangelo SW.

A couple of beginners questions:

1. I see the configure.h is preset to 1/16 microstepping. Is this amount of fine-stepping necessary? I’ve read that steppers wont stop at such accuracies anyway.

2. I actually tried to switch to 1/4 microstepping (changed configure.h and jumpers on A4988) but the motor was moving in a skipping/rocking motion instead. It’s not that your SW does not support this or that I need to change parameters elsewhere right?

3. What would be the easiest way to send a go-to XY position to the Arduino directly, without using the Makelangelo SW? Using GCODE or any other type of command.

4. What does T, B, R and L stand for in the command “M101 [Tx.xx] [Bx.xx] [Rx.xx] [Lx.xx]”? And is this the only start/setup input needed for the robot?

5. How do I set the “length travelled per step”-amount? (I’m guessing the spool diameter is needed?)

Thanks,
Amin

[Dan]

1. Try other settings and report back. I like this setting. good quality drawings, and 1/32 seems excessive.

2. You’d have to change the dip switches under each a4988 to match the software setting.

3. https://www.marginallyclever.com/forums/topic/makelangelo-fans-which-would-be-most-helpful-to-you/#post-15324

4. distance from the origin to the top, bottom, left, and right sides of the machine. For most people L is -(width/2), R is (width/2), T is (height/2) and B is -(height/2). This lets me flip the drawing by swapping left and right, and it lets me move the origin around (tho in practice i don’t at the moment).

5. the equation should be in the polargraph.h file. circumference of spool / (normal steps per turn * microsteps). gt2 pulleys with 20 teeth have a pitch circumference of 40mm. if your motor is 200 steps and you have 1/4 microstepping then it’s 40/(200*4).

Note that string on a spool was abandoned because the string winding changes the diameter in an inconsistent manner, which really messes up the drawing quality.

[Amin]

Thanks for the reply!

QUESTION 3:
That’s a great list, but I was more referring to “how” one should send the commands. I guess serial is the most common way?

I saw that you have made this tool back in 2014, is this what you’d still recommend?

GCodeSender v1, the Better Arduino Serial Window

Do I just make a *.txt file with a bunch of command lines, then open it in the above tool and press send once? Or is there more hacking involved?

QUESTION 4:
With “origin” you mean the starting point of the gondola/pen – it could be in the center of the drawing area or anywhere else within right?

According to another forum post, these measurements are from origin to “bottom right corner of the left motor” and “bottom left corner of the right motor, in millimeters”. So I’m assuming that somewhere in the code you are working out the distance from the motor corner to where the belt actually leaves the pulley? (to get the belt length math right)
However, for me using a custom setup and different diameter spool, won’t this distance need to be altered? If so, where?

[Author]

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