Interesting Read on Microstepping

[Eaglezsoar]

http://www.ebay.com/gds/Microstepping-V ... 664/g.html

[Jimustanguitar]

Very interesting, thanks for sharing! The benefit in smoothness is definitely a plus.


As far as the negatives go, the degree of inaccuracy is kind of subjective, in my opinion... Here's why I say that.

If you relate full steps to whole numbers, and microsteps to the decimals in between... Let's say that the machine needs to move 1.5 steps.
A full step machine can only move 1 or 2. The move will be off by .5 no matter what. It will very precisely move to 1 or 2 with zero discrepancy, but it just cannot move 1.5 by circumstance.
A microstepping machine can "aim" for 1.5, but it might be inaccurate by .1 or .2 because of friction/current, etc. There is not absolute precision between full steps, but being .2 off is better than .5.

Is that flawed logic? A little less accuracy at a higher resolution is still higher precision, in my opinion. Unless you designed your part to make every dimension use full steps, I still feel that being a few 1/16th's off is better than being 1/2 off.

[Eaglezsoar]

Very interesting, thanks for sharing! The benefit in smoothness is definitely a plus.


As far as the negatives go, the degree of inaccuracy is kind of subjective, in my opinion... Here's why I say that.

If you relate full steps to whole numbers, and microsteps to the decimals in between... Let's say that the machine needs to move 1.5 steps.
A full step machine can only move 1 or 2. The move will be off by .5 no matter what. It will very precisely move to 1 or 2 with zero discrepancy, but it just cannot move 1.5 by circumstance.
A microstepping machine can "aim" for 1.5, but it might be inaccurate by .1 or .2 because of friction/current, etc. There is not absolute precision between full steps, but being .2 off is better than .5.

Is that flawed logic? A little less accuracy at a higher resolution is still higher precision, in my opinion. Unless you designed your part to make every dimension use full steps, I still feel that being a few 1/16th's off is better than being 1/2 off.

I agree, and see your logic. I did think it was a good article that's why I posted it plus I was hoping it would generate a dialog that we could all learn from.

[Eric]

However, the power factor could be an important consideration on something like a direct-drive extruder. Especially if you don't need the higher resolution of micro-stepping.

[Eaglezsoar]

However, the power factor could be an important consideration on something like a direct-drive extruder. Especially if you don't need the higher resolution of micro-stepping.

Would it even be necessary to use micro-stepping on the extruder stepper?

[Jimustanguitar]

However, the power factor could be an important consideration on something like a direct-drive extruder. Especially if you don't need the higher resolution of micro-stepping.

Not if you're using a gear reduction stepper.

On a direct drive, it depends on nozzle size, layer height, print speed, etc... A friend of mine was using the .35 nozzle and printing .07mm layers. The direct drive extruder was barely moving. I'm sure that in a case like that, you'd be able to see the steps in a part's perimeter. Especially if you were printing at a low speed.

[bubbasnow]

if we really cared about accuracy beyond what we are getting now, wouldent we just use an encoder?

[Jimustanguitar]

if we really cared about accuracy beyond what we are getting now, wouldent we just use an encoder?

You mean closed loop controllers?

[bubbasnow]

if we really cared about accuracy beyond what we are getting now, wouldent we just use an encoder?

You mean closed loop controllers?

yar

https://www.youtube.com/watch?v=yS7BUTQoN0A

how do i get these youtube videos to embed in a post?

[Captain Starfish]

Nice article, and from an interesting source! Thanks for sharing.

Extruder - I think you'd find that retraction speed would become an issue with a geared unit. Also, given that the steppers we're using already have the power to simply shred the filament with the hobbed gear, there's no need to go to any more shove.

On the columns? I did some embedded work about ten years ago using crappy stepper drivers (L293 rings a bell) which were only full-step. One of the problems we had was step rate vs micro clock rate and finding even multiples for the rate control. Adding 4x or 8x the steps would have made things a hell of a lot smoother, as I can see here. It's nice having fast columns, gearing it down is going to make it noiser, slower, and will introduce geartrain backlash issues. No thanks, I reckon the 4x or 8x microsteppers are just fine.

As to accuracy, my take on it is that these machines are already accurate to within the limits of sag on the cooling plastic anyway. Not a lot of point in having an effector platform that will position to within 10Å when the settling of the filament can mean it's out by 50µm or more.

I gave up with steppers on my Hafco HM-10 mill and these were twice the size of the ones we're using on the Max running at 48 or 65V. Even with the gearing provided by the leadscrews, they just didn't have enough ooomph to feed anything more than timber/plastic and even then it was light cuts only with a small spindle. Forget any deep hogging or facework.

If I went back to reboot that little project it would be with multiphase motors and some serious gearing with a rotary encoder somewhere in the gear train (at the motor means no closed loop around backlash but at the leadscrew means reduced resolution).

Horses for courses, and I reckon the horses chosen for the Max and apparently most of the other 3DPs out there are about the right compromise for the application.