Is it possible to slow a stepper using stall detection?
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I've got an application where I'd like to use a stepper driven axis to compress melted plastic within a mold, and as I've already got some Duets, I thought I could drive the ram via a stepper and instead of stopping or rehoming as would be done on a printer, I could reduce speed to maintain a steady current draw.
Is this out of the realm of possibility and achievable with current firmware?
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@mortarart Side question; on the Wiki at; https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors
It notes that you should use 32v power for the Duet 3 and larger stepper motors like Nema23 and Nema34. Why is 24v insufficient?
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Building current level in the motor coil takes time, and if you run a stepper at a higher current, the higher voltage compensate for that (assuming same inductance and same max steps/sec). If you don't care about high rotation speed, 24V should probably do.
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I very much doubt it; by the time a stall is detected by the driver IC, it's probably already losing steps and the position would be lost. It's not intended for that type of use.
However, if position tracking is not important, you could just set a reduced driver/motor current using M913 whilst in that mode to whatever percentage is needed so the motor provides the required torque and run it continuously.
https://reprap.org/wiki/G-code#M913:_Set_motor_percentage_of_normal_currentIt would be slipping step-wise but providing a steady force to the axis.
Then re-home it after the process is complete, if position is important, or start / stop it as needed, something like an extruder? -
@rjenkinsgb position shouldn't be important during the ramming procedure. Only for the start of and end of the ram, which can be set using end stops!
So I think you've confirmed that this indeed useful to me. Thank you.
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The only other thing to beware of is that the motor is kept below the speed it can start instantly from.
If it stalls or "slips" at above that speed, it may never restart, as the acceleration ramps that allow higher speed only occur when the control system starts & stops the motor.
