Stepper Motor Upgrades to Eliminate VFA's (Vertical Fine Artifacts)
 

Stepper Motor Upgrades to Eliminate VFA's (Vertical Fine Artifacts)  

Page 43 / 44
  RSS
vintagepc
(@vintagepc)
Noble Member
Posted by: @chocki

I think you will find that this is actually a limitation of the 8 bit Einsy board.

A curve is not actually a curve as such but many small straight lines which create the curve and this is what you are seeing, jerk values have a big influence on this as well..

I'm sure Guy can explain it better.

Ah, I'd expected as much. This is where we just need more grunt to handle more uSteps. But just to clarify- I'm aware of the reduction of curved surfaces to polygons. But on large enough ones, I'm seeing artifacts within a single such planar "face".

 

Posted by: @jondamora

Note on the above post, I do not have the mmu installed so I was hoping for the extra resolution by not reducing the microstepping, let me know if I am wrong in that.  Thank you for your work.

Those motors are fine (they are OMC) and I have them.

You *will* need to drop your microsteps for X/Y. The Einsy simply can't handle 200 steps/mm w/ 16 usteps.

This post was modified 3 months ago 2 times by vintagepc
Posted : 04/11/2019 11:35 am
jondamora
(@jondamora)
Active Member

so in the meantime, I got it to work, my firmware changes for some reason didnt work so I just m92'd it and m500.  What exactly would be a symptom of the einsy being overwhelmed by this?  Because I am printing just fine with it as of now.  I have done it slow to start with, but I have a relatively fast print going at the moment, and there are no pauses or jerks or whatever.  I also added a small fan blowing on the einsy board backside to aid in stepper driver cooling just in case, as I do not have heatsinks small enough right now.  What issues am I missing? 

 

Or are you saying only on the x/y axis?  I will definitely do it there, but I am wondering if the extruder can handle it.  Not that it will really make a difference due to the nozzle pressure basically acting like a spring that filters all my precious resolution...

 

As for the OMC/stepperonline steppers, yes I realized that soon after posting, but I am brand new and it wouldnt let me edit my post.  Thanks though.  

This post was modified 3 months ago by jondamora
Posted : 04/11/2019 12:19 pm
guy.k2
(@guy-k2)
Noble Member

What exactly would be a symptom of the einsy being overwhelmed by this?  Because I am printing just fine with it as of now

The printer will appear to work correctly and it actually will for simple geometry. However, if you print something with lots of small curved details you will get short, several mm long, straight line segments where the EINSY skips intermediate positions in curves. When the firmware calculates the next few positions are too fast for it to keep up, it skips over a few positions to keep the print going.

For a long time, I thought the 0.9 x and y motors had insufficient torque for the rapid direction changes, but eventually worked out it was the EINSY not being able to keep up with fine detail printing. The overall geometry will be preserved, but you will find little artifacts during complex prints. My test prints were 10 to 12 hour long topographic maps printed on edge. Mountain ranges were just the kind of complex geometry to overrun the EINSY.

Posted : 04/11/2019 3:55 pm
jondamora
(@jondamora)
Active Member

@guy-k2

I apologize if I am being dense, but is this just for the x/y axes?  Or can the extruder overwhelm the puny 8 bit micro? 

 

PS I can't wait until I get my smoothieboard v2, I am dumb for getting the pro version though because my wait will be much longer.

 

Thanks for all your work and help.

Posted : 06/11/2019 3:01 am
vintagepc
(@vintagepc)
Noble Member

It is recommended to keep extruder steps/mm well under 1000 else you can also encounter it skipping when doing fast retractions or filament load/eject.

Posted : 06/11/2019 3:33 am
jondamora
(@jondamora)
Active Member

Update, I have started getting extruder "clicking" which only goes away by reducing speed.  I take this to mean I have exceeded the limits of the hardware in some way and must reduce the microstepping.  For reference, I tried to use a 0.9 stepper with full 1/16 microstepping and failed, as everyone here told me I would.  Well I am still glad I tried.  Thanks for your help e'erybody.

Posted : 08/11/2019 7:35 am
david.a66
(@david-a66)
Honorable Member

@jondamora

that sounds more like you have exceeded the extrusion capacity of the hot end.

Posted : 11/11/2019 6:19 pm
jondamora
(@jondamora)
Active Member

That is what I meant by "exceeded the limits of the hardware in some way", but I cant be sure exactly so I left it vague.  And really I have been wondering, how can people get away with using a geared extruder on the stock rambo board?  Wouldn't that triple the steps per unit, and cause the extruder to overwhelm the 8 bit micro even more so than my doubling?  Maybe my issue was not too many steps.  I have some more testing to do.

Posted : 13/11/2019 8:21 am
david.a66
(@david-a66)
Honorable Member

clicking usually means you are trying to extrude faster that the hot end can melt the filament

Posted : 13/11/2019 7:59 pm
chocki
(@chocki)
Honorable Member

It may also be your speed vs torque.

With the geared setup, at the filament drive, the 1.8 Deg motor happened to sit well with extrusion speeds vs good torque and voltage required to achieve it.

A 0.9 Deg motor ungeared will produce less torque to begin with at the filament drive and will be running at a different speed which may not be optimal for torque.

You could try increasing the drive current.

 

Oh found the posting on Thingiverse where I did some working out about stepper motors and torque etc This is for the OMC Stepperonline motors, but may give you a clue what to check for in your case:

 

I'm hoping that due to it being a lower current motor, it will have more windings and may produce more torque sooner (Slew rates of driver) than the higher current motor. Granted the 1A motor will produce more overall torque and at higher speeds, but we are not using this stepper anywhere near speeds where any of this matters. in both cases maximum torque occurs at around 75 rpm, the 100 motor produces around 1200 gcm torque at 1000 ma whereas the 070 motor produces around 1060 gcm at 700 ma, so if we apply a very rough rule of linearity to both motors, at 700 mA the 100 motor would only be producing 840 gcm.
I know steppers arent quite as simple as this, but if it responds quicker and produces more torque at slower speeds and currents, then surely this can only be better.
Well, I'm going to find out 🙂

 
 
 

Here we go, finally got the information together on why I think this motor 'may' be a better option. Since it is a lower maximum current motor, I'm hoping it gets closer to its 63 % therefore producing more torque than the 1A motor will, at about 441mA to be precise which happens to be right in the ball park for what Prusa are driving this extruder motor at, ideally we want to set the current to this for maximum torque.
Granted we could drive the 1A motor at 630mA, but asuming the rate that the power increases from 0 to maximum remains constant, the lower current motor will achieve maximum torque sooner than the higher current motor also more current = more heat which we don't really want anyway. ( I may have this all wrong, but only one way to find out! - Everyday's a school day!)

Taken from here: https://www.motioncontroltips.com/what-stepper-motor-type-is-best-for-high-torque/

Hybrid stepper motors have the ability to produce higher dynamic torque, but in order to make this happen, the electrical time constant of the motor must be taken into account. The electrical time constant, τe, is the amount of time that it takes the current in the windings to reach 63 percent of its maximum value. Because torque is proportional to current, the current needs to be at its maximum in order for the motor to produce maximum torque. And, maximum current (and hence, torque) must be reached before the current is switched to the next phase.

In order to achieve this, the voltage supplied to the motor must be higher than the motor’s rated voltage. The higher the ratio of supplied voltage to rated voltage, the faster the current will enter the windings and reach its maximum value. Hence, maximum torque can be produced before the current is switched and the cycle repeats.

 
 
 

The Stepperonline 17HS10-0704S works perfectly, but then again so did the 17HS08-1004S.
I thought that after reading about the slight underextrusion upon restart that it might help with bridging, or rather just the first strand which most of the time apears to start late so drops, but alas, it made no difference to this.
I'll leave it on for now and run some more tests when I get a bit more time so see if there is a difference in print quality.
Just for the record, motor went straight on, no wiring issues or anything negative. I did order it direct from https://www.omc-stepperonline.com/
at £8.05 and a couple of £ shipping in the UK, I thought it was worth a try, the 17HS08-1004S is £7.82 from here if anyone in the UK is after one, they also have supplies in the US (cheaper than UK) and worldwide.

 
This post was modified 2 months ago by chocki
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 14/11/2019 12:51 pm
chocki
(@chocki)
Honorable Member

Oh and since then the part about dropping the first strand when bridging, it's all to do with the k value for the filament. Back in April, I did not know enough about it.

Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 14/11/2019 12:54 pm
chocki
(@chocki)
Honorable Member

If you look at a typical torque curve for a 0.9 Deg motor of about the right size, you will see maximum torque occurs at 150 rpm.

If you are not geared, you will be running well down on the rpm scale where torque drops off the cliff so to speak.

https://www.omc-stepperonline.com/download/17HM15-0904S_Torque_Curve.pdf

 

A geared extruder really is a good thing as the torque increase is more than just the ratio of the gearing, it also brings it closer towards the maximum torque running speed of the motor.

This post was modified 2 months ago by chocki
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 14/11/2019 1:03 pm
Przemo-c
(@przemo-c)
Active Member

I know this thread focuses more on the 0.9deg motors. But i've done the drop in replacement for Y axis of 1.8deg moon one and improvment in both VFAs and how quiet it runs.

 

But in stealth mode it stalls a lot spreading the layers across the Y axis. The platform moves easily when i tilt the printer it slides around on its own.

 

Is there any tuning nescessary/possible for the 1.8 deg moon motor to get the most out of it?

 

I don't need stealth for that motor as it is pretty quiet in normal mode but for quieting other stock motors.

Posted : 22/11/2019 8:17 am
guy.k2
(@guy-k2)
Noble Member

It is odd that you are having a significant change in torque simply switching to a 1.8 moons. There should not be any need to change settings if it is a Model MS17HD2P4100. Is it a limited wavering back and forth shift or a gradually worsening large shift? If limited/wavering, I would check the drive pulley set screws.

However, you are seeing this in STEALTH which suggests an overall friction issue despite the platform sliding with gravity. Probably should check with belt detached to confirm near zero friction.

This post was modified 2 months ago by guy.k2
Posted : 22/11/2019 5:13 pm
Przemo-c
(@przemo-c)
Active Member

@guy-k2

This is the model i have.  The shifts are major (like one move gets stalled about 20mm) and go in one direction only then it "settles" at the end i guess it cant Shift any further. Belt status shows 275 for Y axis with belt pretty tightly set. I've tried with very loose belt (but not skipping) but in stealth it still happened. Curiously I've printed more of an oval print (roku remote stand) and there were no shifts.

I've checked that the belt doesn't skip

I've checked if the gear is properly tightend on motor axis.

With belt attached and pretty tight but steppers disabled platform moves on it's own somwhere above 30 deg of tilt. With belt detached at around 10 deg of tilt.

In normal mode works like a charm with no crashes detected. Even at 125% of speed.

Posted : 22/11/2019 6:11 pm
guy.k2
(@guy-k2)
Noble Member

Ok. Rods and bearings appear to be OK. Any chance the heater cable is bumping or dragging over something?

With that ruled out, I would hesitantly suspect a bad motor specimen.

Posted : 22/11/2019 10:04 pm
Przemo-c
(@przemo-c)
Active Member

Nothing is bumping into anything i watched how it stalled. I will recheck the wiring as i've spliced 2 cables maybe when i was routing the cables i got a bad connection and there's too much resistance... if not i'll replace it with another moon motor and check.

 

BTW thank you very much for investigating that issue so well. I've been doing some anatomical models for a friend in medical school and it infuriated me that those artifacts were so prominent. Now they are nearly gone.

Posted : 22/11/2019 11:03 pm
cecilliac282
(@cecilliac282)
New Member

you can have lookt at 17HM15-0904S here

https://www.oyostepper.com/goods-60-Nema-17-Stepper-Motor-Bipolar-09-deg-36Ncm-51ozin-09A-54V-42x42x40mm-4-Wires.html

Posted : 18/12/2019 10:25 am
cecilliac282
(@cecilliac282)
New Member
Posted by: @cybrsage
Posted by: vintagepc

Just a heads up, this appeared in the firmware github recently. Future builds will probably have linearity correction disabled...

https://github.com/prusa3d/Prusa-Firmware/commit/4e7de776cd5c9cc2d6aa5a80c6269edf4a379f3b#diff-d1d79099d6fb1bd5281c9ea0deb5060c

https://www.oyostepper.com/category-1-b0-Hybrid-Stepper-Motor.html

So no more stock firmware with motors that need said correction for better performance... :-/

Which steppers need it?

 I have similar question as u.

Posted : 18/12/2019 10:38 am
vintagepc
(@vintagepc)
Noble Member

PSA: The reset on some homing attempts was a buffer underflow in the code. It's been corrected and the fix will be in  3.9.x

Posted : 18/12/2019 1:49 pm
Page 43 / 44
Share:

Please Login or Register