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o_lampe
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dc42
A motor current rating of 2.4A is way too high for any sort of plug-in driver.
I thought I could run them with much lower current, since their torque rating is pretty high. 2A+ is no problem for RAPS128 drivers.
Now I'm hesitating buying 1.2 or 1.7A 0.9° steppers. Will they be good enough for extruder direct drive?
The problem with using a high torque motor and running it at (say) 30% of maximum current on the grounds that you don't need more than 30% of the rated torque is that with high torque you also get high rotor inertia. So you need to use low acceleration and jerk so that the rotor inertia doesn't keep the motor position too far behind where it is wanted resulting in missed steps. Personally I always use at least 60% of the rated current, although I have known printers run at 50%. So perhaps I should have said "rather too high" instead of "way too high".
If I were using a direct drive (i.e. non-geared) extruder, I would choose a high torque motor and want to be sure of being able to run it at up to 85% of its rated current. So a 1.7A motor would be no problem for a Duet, but would be marginal with most plug-in drivers. I don't know the specifications of the RAPS128, but unlike most plug-in drivers the chip is designed to be cooled from the top, which means that a heatsink and fan can provide reasonable cooling.