Optimizing Duet setup regarding stepper current, jerk and speed

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DeltaCon
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Optimizing Duet setup regarding stepper current, jerk and speed

Postby DeltaCon » Thu Jun 15, 2017 4:37 am

Hi all,
This is basically a continuation of this thread:
viewtopic.php?f=112&t=11991&p=105403&sid=04f4642ef8258df5add44c4098a74e28#p105355
But I felt I hijacked wdmarine's thread and was wandering off-topic too much. But it is keeping me busy, hence a new topic in the correct subforum (although this might be of interest to users of other controllers too).

The info in the above mentioned topic made me curious about my own stepper motors, and I checked them out to be Wantai 42BYGHW811P2. I googled for specs: http://www.phidgets.com/documentation/P ... asheet.pdf . Here it shows that they are rated for 2.5 Amps, which looks to be much higher then most others?

Using the formula for calculating the maximum speed (as found on the Duet3d.com wiki) as:
max speed = (4 * pulley_teeth * supply_voltage)/(steps_per_rev * pi * inductance * current) I get this result:
StepperCurrentFormula.png

But I am having troubles interpreting it. Obviously 0.737 is no nice speed. Would I have to use mA instead of A, then the is even worse. Assuming meters/second the outcome is unreasonably high... What am I missing? And how can I optimize the jerk setting?

Reason I am asking all this is that I have a lot of stringing problems in my prints, and I think I can at least partly counter measure that by optimizing jerk and move speeds, so that the string breaks. It does not do that now. I already put a lot of effort in optimizing retraction settings and extrusion temp... My current config in the duet is this:

Code: Select all

M906 X1200 Y1200 Z1200 E1400 I60     ; Set motor currents (mA); set each extruder explicitly

M201 X1000 Y1000 Z1000 E1000         ; Printing Accelerations (mm/s^2) Set all E-motors the same
M202 X2000 Y2000 Z2000 E1000         ; Moving Accelerations (mm/s^2) Set all E-motors the same (Not sure it's used in DC42 Duet firmware!)
M203 X20000 Y20000 Z20000 E3600      ; Maximum speeds (mm/min) Set all E-motors the same
M566 X1200 Y1200 Z1200 E1800         ; Maximum instant speed changes mm/minute. Set all E-motors the same


But If my motor current can be upped, I presume acceleration, speed and jerk can also be upped big time.
All tips are welcome, thanks!
I am DeltaCon, I have a delta, my name is Con, I am definitely PRO delta! ;-)
Rostock V2 / E3D V6 / Raymond Style Heatchamber on the way!

PS.: Sorry for the avatar, that's my other hobby!

dc42
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Re: Optimizing Duet setup regarding stepper current, jerk and speed

Postby dc42 » Fri Jun 16, 2017 1:35 am

You need to enter the inductance in Henries, then you get 737mm/sec. It's mm/sec not m/sec because the formula assumes a 2mm belt pitch.

The reason it is so high is that the motors have low inductance and you are running them well below their rated current. You could certainly increase the current to get more torque. However, the cure for stringing is usually to reduce extrusion temperature.

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DeltaCon
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Re: Optimizing Duet setup regarding stepper current, jerk and speed

Postby DeltaCon » Fri Jun 16, 2017 3:54 am

Thanks DC42.

Yesterday night I upped the steppercurrent to 1500mA, the max speed from 20000 to 30000 mm/min and the jerk from 1000 to 1500. I have been printing brackets for my enclosure for hours. I can feel the motors getting a bit warmer then before. I measured them around 47 degrees C so that is really no problem. It looks like the stringing became a bit less, but I did not make any changes in my slicer setting. So the max movement is not reached at all. It could be that the jerk has some effect though, but it is not really noticeable in machine behavior. Also I calibrated the temp sensor of the Duet board like you mentioned yesterday in the other thread. And barely see any higher board temp. than usual. It is keeping temp at about 33 degrees C. So to my guts that all feel fine. What is considered to be a max safe temp to run a Duet 0.6?

Given the high current rating of 2.5A for my steppers and the cool board temp of my Duet 0.6, is it wise to up the stepper current a bit more? That would lead to lower max speeds (given the formula above) but 700 mm/sec sounds incredible and as far as I know most users use like half that speed, so I am not loosing a lot there I guess. Besides printing at those speeds will most likely over-demand my EZ Struder anyway. But are there any other advantages I can get when upping the current a bit more?
I am DeltaCon, I have a delta, my name is Con, I am definitely PRO delta! ;-)
Rostock V2 / E3D V6 / Raymond Style Heatchamber on the way!

PS.: Sorry for the avatar, that's my other hobby!


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