Hello fellow polargraphers

1st off i wanted to say how exciting this project is to put together my hats off to you sandy 🙂

I was wondering if anyone could help with a little problem im having.

This was my machine:

This is it now:

Initially i had it up and running (it was so exciting to see it move) After i had taken some measurements (to make its project box). Then put it back together it started to act a little weird:

when trying to do a pen test the right motor will move but then the left stayed still and stiff.

then i tried to do a test vector and it would just move then stop then move again.

only time it moves the way it should is when i do "move pen to point"

this is the result after all of the above:

thank you for reading my post

Three bad usb cables in a row seems bad luck but I've had a bad batch before too. By coincidence I was hitting my head against a wall the other day with a problem where the motors would lock the motors and not move, but it worked when I tried a different cable. But then _stopped_ when I moved the new cable back. Turns out the problem was actually with the pins from the motorshield, they just weren't making good contact with the pin sockets on the arduino... Just slightly too small, very slightly. It appeared to work fine with the new cable because that was plugged in on the desk instead of above the machine, and so the motor cables exited at an angle that stressed the connection... Not visible, and couldn't even feel a difference pressing, but slightly incompatible pin headers.
Those stacking pin headers aren't so good.
Very glad you got it sorted out!
Sn