Increase Extruder Motor Current Limit
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Both the flex3drive and nimble require to use low motor current, the motor can't make a fast direction change at high current as quickly. I use 500mA with nimble and a 34mm motor. A 20mm pancake motor or nema 14 would also work. Acceleration needs to be low 120 to facilitate the direction changes. Jerk at around 40. More motor current is a red herring.
In my experiments with a nimble and a pancake stepper I had to go to 600mA. 500mA and less the stepper stalled on high extrusion speeds. (~12-16mm^3 on a 0.6mm volcano nozzle).
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What acceleration were you using? A stall is less likely with lower acceleration, (or higher current) but this apparently makes reversing direction slower.
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Definitely the smaller one. You hardly need any torque at all, the gearing is 40:1, I suspect a nema 14 would handle it. You need the ability to turn fast (low inductance) and reverse direction quickly (low inertia).
24v better, but it'll work on 12v.
I wouldn't see much use for that larger motor in 3d printing except maybe for driving a really heavy bed moving in Z, where torque is everything and speed nothing, ability to reverse only needs to be quite modest.
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Thanks. BTW, it is a NEMA 14
The large motor could be used as a direct drive extruder, as it has same torque as common Nema 17. It is longer, but has a smaller section.
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Ahh yes.. but still the torque is plenty, I drive titans with 20cm pancake nema 17 with 13Ncm torque and this works great, a 30:1 (nimble) or 40:1 (flex3drive) no issue at all.
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While we are on the subject of flexible drive systems:
I noticed that my machine was having small variations in flowrate. Small enough that it still made parts pretty well but large enough that it makes the exterior surfaces rough. In an attempt to figure out the issue, I slowed the machine way down and it was still present but at slow speeds I was able to see torsional flexing in the drive shaft at a frequency that looked similar to the changes in flowrate from the nozzle. I knew the grease in my worm gears was likely dried out. I cleaned them and reapplied Krytox. So far it seems to have remedied the problem.
While investigating, I did notice that the flex3drive seems to be configured in such a way that the torsion on the drive shaft while extruding will cause the outer wire windings to expand rather than contract. Just using my hand, I can feel a significant difference in the hysteresis between the two directions. It seems to me that it would be better to have the driveshaft turning the opposite direction (or wound in the opposite direction) so that the outer windings would tend to contract and improve the stiffness of the system when extruding rather than retracting.
I know that flexible drive shafts have a higher torsion rating in one direction versus the other but do not recall which direction relative to the winding that is.
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I hear a lot about this but do not notice it either with flex3drive or nimble, perhaps I'm not looking closely enough. With nimble since you can mount it either way then, in theory, you could configure it by your thinking above, to run in the "optimal" direction for extrusion. Whilst some people report feeling slightly more tension in the drive cable at a certain point on its rotation I'm unconvinced this affects print quality, just because there is more resistance, doesn't mean it actually turns more slowly.
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If the torque on the shaft changes enough, there will be a different angle from end to end (this angle depends on the torque, and is a data of the shaft). In this case, it is not surprising to see variations on the extrusion.
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I hear a lot about this but do not notice it either with flex3drive or nimble, perhaps I'm not looking closely enough. With nimble since you can mount it either way then, in theory, you could configure it by your thinking above, to run in the "optimal" direction for extrusion. Whilst some people report feeling slightly more tension in the drive cable at a certain point on its rotation I'm unconvinced this affects print quality, just because there is more resistance, doesn't mean it actually turns more slowly.
It only became a problem when the grease on my worm drive dried out. I do run my flex3drives in an 80C chamber. The problem came on so gradually that I didn't really notice or do anything about it until now. I'm seeing differences in flow rate of about 7% and M572 calibration of about 0.03 while also getting much smoother extrusions.
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So keep em greased up.
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I ended up buying the Nema 8 below and making an adapter plate for it. Running it at 500ma,
Jerk 90, Acceleration 75. I use an advance of about 0.06 when using a 0.4mm nozzle.So far it seems to work great and has really helped keep the speed up and made retractions much faster. Hasn't stalled even when manually commanding it at 10mm/s (24mm^3/s) through at 0.4mm nozzle. I don't expect to ever print that fast with that small of a nozzle but just wanted to make sure it wouldn't stall when I wound it up to full speed.