Extruder acceleration/jerk and tuning

Ringo1508

@deckingman said in Extruder acceleration/jerk and tuning:

As @Phaedrux says, the max speed should be set for the maximum travel speed (e.g. I use 350mm/sec for non-print moves but usually print at around 90mm/sec). Personally, I calculated the maximum attainable speed based on the maximum acceleration that the motors will give me for the mass and bed size and set that in config.g. So it's nice and high and won't limit what I do with my slicer.

You could add a step between 7 and 8 - set maximum accelerations for moves rather than axes - see M204 https://duet3d.dozuki.com/Wiki/GCode#Section_M204_Set_printing_and_travel_accelerations. This can actually be useful on a per-print basis rather than being in config.g though.

Sorry to dig up an old thread @deckingman but I'm hoping to keep this all in one thread so if someone finds it searching for the same reason I did, this info will be here too!

@deckingman, how did you calculate the "maximum acceleration that the motors will give me for the mass and bed size"?

I'm just now diving into the black arts of tuning and I have no idea how to tune acceleration, feedrate (speed?) and jerk.

The EMF calculator says that I'll start losing torque on my X/Y axis around 254.8mm/s so I was going to set M203 X and Y to 250mm/s (max speed) and then M204 T to 250mm/s (max travel speed) as you suggested (if I understood you correctly on this.) I just have no idea how to figure out max acceleration.

deckingman

@ringo1508 said in Extruder acceleration/jerk and tuning:

@deckingman, how did you calculate the "maximum acceleration that the motors will give me for the mass and bed size"?

It's a long, long time since I did the calculations but I used a spread sheet to do the calcs. This was later updated and improved upon by user @wilriker and he posted it online somewhere. Sorry but I can't off hand find a link. Maybe he'll see this post and jump in or if not, try sending him a PM.

Basically it comes down to Force = Mass X acceleration so if you knowe the mass and the force, you can calculate the acceleration..............................

....................As I'm in a generous mood, I've just dug out my old spreads sheet which went something like this:

Quoted holding torque = 59N.cm at max current.
Assuming 85% max current is used then torque becomes 50.15 N.cm
Take 70% fudge factor for loss due to micro stepping gives 35.61 N.cm
Use 50% fudge factor for loss at speed gives 17.8N.cm
Pulley diameter = 12mm, so radius =6mm (0.6cm)
So available force = 29.7 N
X carriage mass at that time was 1.67Kgs
So acceleration becomes 29.7 / 1.67 = 1.77m/sec^2 or 17,767 mm/s^2.
But assume only 10% of this for a single micro step then becomes 1,777 mm/s^2

As I said, there were lots of fudge factors in the calculation and some things missing but IIRC the result was a conservative estimate. @wilriker did a better job of the calculations than I managed.

Once you know the maximum accelerations, then the maximum attainable speed (assuming an initial velocity of 0) can be calculated from sqrt(2 x acceleration x length\2). The length would be the diagonal across a rectangular bed or the diameter of a circular bed.

HTH

Ringo1508

@deckingman awesome!! Thank you so much.

wilriker

For completeness here's the link to my online Maximum Acceleration Calculator.

deckingman

@Ringo1508 I told you @wilriker would likely step in.

@wilriker Thanks man (uel).

Edit. Manuel - you should put a link yo that in the Wiki (if you haven't already).

wilriker

@deckingman said in Extruder acceleration/jerk and tuning:

@wilriker Thanks man (uel).

If you summon me I come.

deckingman

@wilriker said in Extruder acceleration/jerk and tuning:

@deckingman said in Extruder acceleration/jerk and tuning:

@wilriker Thanks man (uel).

If you summon me I come.

I must stop polishing that old lamp..........

wilriker

@deckingman said in Extruder acceleration/jerk and tuning:

I must stop polishing that old lamp..........

I put a link to the calculator at the wiki entry for M201 - though I must admit that it feels a bit strange to "promote" my own tools in the official GCode documentation.

deckingman

@wilriker The Wiki is there for the benefit of the entire community. You have made your tool avaible, also for the benefit of the entire community. Therefore it is right and proper that there should be a link to your tool in the Wiki.

dc42

@mrehorstdmd said in Extruder acceleration/jerk and tuning:

M593 to cancel ringing- does it affect retraction tuning?

No, it doesn't.

The M566 jerk setting affects how well M593 works. High jerk settings make M593 less effective, or totally ineffective.

DocTrucker

Not mentioned fine tuning of extrusion temp in that original list. It would seem logical to go for linear/non linear extrusion correction checks as soon as your happy with extrusion temp and e-steps/mm.