Stepper does not do exact degrees

[Al-Vista]

• I am using Arduino Uno R4 Wi-Fi, connected via TMC2208 to a 200-step Nema17 motor. The application is a telecine, I need to advance the film exactly one frame per exposure of the camera, so I tried to use the myStepper.write(30) command to rotate the sprocket (which has 12 teeth) by one frame. However it actually loses about 1° per 360° of rotation, so after a few minutes the frames will be completely out of sync.
• I set the steps per rev to 1600 as that is what gives approximately 30° even though the nominal step count of the motor is 200, perhaps the driver is doing micro stepping by itself.
• I have tried reducing the speed in case it is missing steps, but that seems to make no difference. How should I be doing this?

[MicroBahner]

I set the steps per rev to 1600 as that is what gives approximately 30°

This 'approximately' is your problem. Your stepper cannot do exactly 30 degrees. MobaTools tries to adjust as close as possible, but there will be a difference. This is usually compensated when the target angle is increased in 30° steps, for example: 30 ... 60 .. 90 .. 120 .. so the error will not accumulate. But your setZero() with every increment inhibits that.
Therefor define a target position, e.g.
long targetAngle;
and incremnt this with every iteration and don't use a setZero() command:

myStepper.write(targetAngle);
targetAngle += 30;

[Al-Vista]

Thanks! I'll try that.

[MicroBahner]

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