Stalling a Stepper Motor with Silent Stepper Bricklet

[ryan]

Hello! 

I am trying to generate a torque-current curve for the NEMA 17 stepper motor I have using the Voltage/Current Bricklet 2.0 and a Silent Stepper Bricklet 2.0. I have a lever arm attached to the stepper motor, which is powered with 24V. However, every time my motor is stalled (the arm hits a load cell), the motor jitters as if it is skipping steps (as expected).

Is there a way to make my motor not jitter when it is stalled and just draw the appropriate amount of current? What setting should I look into changing? Or is this not possible? Ideally, I'd like it to act like a stalled brushed or brushless motor and draw its stall current without vibrating so much at stall. 

Thank you!

[MatzeTF]

I believe it’s not possible to drive a stepper motor in any direction and have it not jitter, but it should be possible to tell it to stop and adjust the holding current to whatever you need.

This works better with a brushed or brushless motor because they kind of have positional feedback. The brushed motor will inherently switch motor coils when it turns and brushless motors usually use some kind of rotational feedback, often some magnetic sensor. With stepper motors, you have no idea where the rotor actually is and you can only alternate between the coils and hope that the motor moves in the direction you want, which it won’t do when it’s stalled.

If you want to control the holding torque precisely, you could drive it until it stalls, then step forwards in increments of 1 until it jumps back, as visible in your load cell data, then drive it forwards until right before it jumps back and then adjust the holding current.

After having written all that, I feel like someone must’ve solved that properly already. You can’t be the first one wanting to do torque control for a stepper motor.