Hi. I have an issue with ULN2003 and will appreciate help troubleshooting it.

I've built polargraph from acrylic parts, mechanically it works nicely. Here is the photo of my setup:

Arduino UNO has separate 9V 1A power supply.

The code looks like this:

in polargraph_server_a1:

#define UNL2003_DRIVER

const int DEFAULT_MM_PER_REV = 108; // Measured myself
const int DEFAULT_STEPS_PER_REV = 4075.7728; // For 8-step  control signal sequence
const int DEFAULT_STEP_MULTIPLIER = 1;

static float currentMaxSpeed = 1000.0;

in configuration.ino:

AccelStepper motorA(8, 2, 4, 3, 5); // Left stepper. 8-step
AccelStepper motorB(8, 6, 8, 7, 9); //Right stepper. 

  motorA.setPinsInverted(false, false, true);
  motorB.setPinsInverted(true, false, true); // This is from original package
//  motorB.setPinsInverted(false, false, true); // Changing first argument to False didn't help

Any ideas? Thanks in advance.

What happened when you changed the initialisation line and swapped the pairs of wires?

AccelStepper motorB(AccelStepper::FULL4WIRE, 7, 9, 6, 8);

Not sure if you'd need to reverse the whole sequence, or just swap the pairs.

sn

Surprisingly, nothing changed. Not quite sure - either there is something weird with the library or that's me not getting something right. Swapping pairs in all possible combinations didn't work either.

Anyway I gave up - I discarded ULN2003 and am hooking up the steppers directly to MotorShieldV1 (fortunately I have one). I bought the B5B-XH-A connectors to plug 28BYJ-48 into.

As for machine: I didn't have easy access to 3D-printer, so I went for laser cutting. Used 2mm acrylic sheet for sprockets (made of 3 layers, central is slightly smaller, which allows to hold the chain tightly and prevent it from falling on the side). The frame was meant to have holes exactly the size of office clips - they hold the frame very reliably. The drawing surface is the cheapest picture frame from IKEA. Call this "poor man's polargraph" if you'd like 😉

I'll share the AutoCAD drawing of my acrylic parts after I'll make this thing work.

When I use 28BYJ-48 motors, I don't connect the red wires to anything and I drive them as bipolar.
There are quite a few posts about this online, many of which that say you must cut a trace where the red cores connect in the motor, but I've never done that and I've never had a problem, apart from supplying a current that's just right for the motors.

Quote from kongorilla on April 10, 2016, 23:25
When I use 28BYJ-48 motors

Could you please share your configuration? You could use pastebin.com or similar resource to host these. Thank you in advance.

I solved the mystery of motorB going in the wrong direction.
You have to swap the wire pairs.
motorB.setPinsInverted(true) does not really work, it produces dropouts.

This is working for me:
AccelStepper motorA(8, 6,8,7,9);
AccelStepper motorB(8, 5,3,4,2);

I am also unsure about stepsPerRev, I've tried 4096 and multiplier 1

I finally got the gondola to move in the right direction. These are my settings

#ifdef UNL2003_DRIVER

#define motorPin1 22 // Blue - 28BYJ48 pin 1
#define motorPin2 24 // Pink - 28BYJ48 pin 2
#define motorPin3 26 // Yellow - 28BYJ48 pin 3
#define motorPin4 28 // Orange - 28BYJ48 pin 4
// Red - 28BYJ48 pin 5 (VCC)

#define motorPin5 30 // Blue - 28BYJ48 pin 1
#define motorPin6 32 // Pink - 28BYJ48 pin 2
#define motorPin7 34 // Yellow - 28BYJ48 pin 3
#define motorPin8 36 // Orange - 28BYJ48 pin 4
// Red - 28BYJ48 pin 5 (VCC)

AccelStepper motorA(8, motorPin5, motorPin7, motorPin6, motorPin8);
AccelStepper motorB(8, motorPin4, motorPin2, motorPin3, motorPin1);
//AccelStepper motorB(8, motorPin1, motorPin3, motorPin2, motorPin4);

#endif