Dropping extruder motor to 1/4 or 1/8 microstepping

My extruder motor is missing some steps every now and then, and I already have the motor current turned up about as high as i think i can go without melting my PLA extruder mounts due to a pretty hot motor.

Would dropping the microstepping down to 1/8 or 1/4 instead of 1/16 help squeeze a little more torque out of my motors without increasing the current or temperature? (I know i will have to change my E-Steps/MM in the firmware to reflect that change).

I have heard it helps. There is a torque gain from lower microstepping and since the extruder uses such high steps it may not cause any issues. Just cut your steps/mm in half, but obviously you will lose some accuracy.

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If you are skipping slow down the print speed and or acceleration.

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www.Fablicator.com

@C. Cecil
In theory i would think lowering the microstepping would increase the torque, but i was wondering if the increase was significant enough to give it a try. If it's only increases it very slightly it probably isn't worth it and best to figure out other solutions.

@Andrew Diehl
Im only printing perimeters at 30 mm/s and Infill at 60 mm/s (although now that i think about it, my extruder usually skips steps when doing infil). Do you think 30 and 60 mm/s is faster than should be reasonable? Seems like those are pretty common/average speeds.

What would an appropriate acceleration number be? And which of these acceleration variables should i change?
#define DEFAULT_MAX_ACCELERATION
#define DEFAULT_ACCELERATION
#define DEFAULT_RETRACT_ACCELERATION

I am running Marlin, RAMPS, Prusa, J-head MK IV-B 0.5 nozzle

There goes that myth again. Reducing microstepping will not increase the torque when using a constant current driver. The power dissipation and torque are the same in the intermediate positions that you are skipping.

Edited 1 time(s). Last edit at 02/05/2012 06:03AM by nophead.

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[www.hydraraptor.blogspot.com]

Something I read somewhere (here)...but you are right I did not take the constant current into consideration. Good point.

I guess someone could build a jig and do some tests to put the myth to bed for sure.

Edited 1 time(s). Last edit at 02/05/2012 07:47AM by C. Cecil.

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----------------------------------------------------------------------------------------------------------------------------
www.Robosprout.com RepRap Mendel parts and accessories.
Message if there is anything you need...I have more than what is listed on my site.
Located in the Spokane, WA / Coeur d'Alene, ID area.
Contact: Robosprout@gmail.com Flickr: [www.flickr.com]

Yes that is the myth, it appears all over the web. Incremental torque (meaning the increase in torque created by moving one microstep) is lower, but of course it is as torque is proportional to the sine of displacement. In terms of the torque available to hold or move a load it is exactly the same in say the 1/8th step positions as it is the 1/16th step positions. Skipping over the 1/16th step positions and only stopping on the 1/8th step positions doesn't gain you anything. Yes the incremental torque for one step is higher but in the same time you would have taken two steps if you were 1/16th stepping, so the incremental torque would be exactly the same at the same point in time.

In actual fact, what happens when you have high torque load, like the extruder, is the shaft lags behind where it should be, by an angular displacement that generates enough torque to balance the load. That displacement is exactly the same, regardless of how small the steps are.

Yes you don't necessarily increase accuracy when you reduce the microstep size, but you don't make it any worse, and you don't reduce the torque.

Edited 1 time(s). Last edit at 02/05/2012 08:53AM by nophead.

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[www.hydraraptor.blogspot.com]

Thank you for the explanation. Sounds reasonable.

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----------------------------------------------------------------------------------------------------------------------------
www.Robosprout.com RepRap Mendel parts and accessories.
Message if there is anything you need...I have more than what is listed on my site.
Located in the Spokane, WA / Coeur d'Alene, ID area.
Contact: Robosprout@gmail.com Flickr: [www.flickr.com]

Wow thanks for that explanation Nophead! That's really helpful to know! So i won't bother reducing the microstepping for my extruder motor.

I still think there may be an acceleration issue though. Any thoughts on what a reasonable setting would be?