Stepper motor jitter

Other Hardware Motors, Mechanics, Power and CNC
1

Hello, I'm using an Arduino Uno and the Adafruit motor shield to drive two stepper motors, as shown in the picture (attached). Having spent a while working on it, the motors are getting all the power they need and there is enough torque.

The issue is when I program the motors to take individual steps. After each step the 'arm' oscillates (only briefly) a little - however I'm after very fine precision, so I need to remove this completely.

Does anyone have any suggestions on removing the jitter? I'm struggling to work out whether it is a fault of the mechanical assembly or the motor itself, and if known what could be done about it.

Thanks for any help!

WP_000029.jpg
WP_000029.jpg1632×1224 545 KB

2

You need to post your code if you are going to ask a question like that.
(and it's "jitter" not "judder")

3

Jitter is about timing variations.Jitter - Wikipedia

Judder: "To shake rapidly or spasmodically; vibrate conspicuously". I'd call this
particular effect ringing or oscillation anyway.

Anyway the solution is to use a microstepping driver, not an H-bridge. Or possibly add mechanical damping.

4

I'm using the AF stepper class, and the board should support microstepping. This is the code I'm using:

AF_Stepper motor(200, 2);

void setup() {
    motor.setSpeed(1);
}

void loop() {
   motor.onestep(FORWARD, DOUBLE);
   delay(1000);
}

But if I replace the stepping line with

motor.onestep(FORWARD, MICROSTEP);

then the motor oscillates on the spot and won't turn.

Adding mechanical damping is an interesting idea - any suggestions on implementing this with my setup?.

5

The AF_Stepper class does not appear to implement acceleration profiles? If you are stopping without acceleration, then the moving mass will cause some oscillation about the final step point. In the worst case it could lead to missed steps.

It appears that using this library microstepping doesn't work with single steps, the library starts and stops on a full step. You would need to perform a multiple of the microstep interval (16 may be the default) per call to get proper results.

Which version of the motor shield have you got? The V1 motor shield and library are pretty basic, you may struggle to get precise operation from it. The v2 board looks better, but a4988 driver or similar and accelstepper might be a better option.