Does M204 limit extruder acceleration?

Khumarahn

just checking, since I could not understand this from the documentation

RepRapFirmware applies the M204 accelerations to the move as a whole, and also applies the limits set by M201 to each axis and extruder.

deckingman

@Khumarahn Extruders are treated like axes and are synchronised. So every axis and extruder which is commanded to move as part of a G1 command, will start and end it's move at the same point in time, regardless of the length of each axis or extruder move. If that was not true and one changed the acceleration of the X and Y axes but not the extruder, then the extruder would start and/or end it's move before or after the axes, which clearly cannot be allowed to happen.

Khumarahn

@deckingman Suppose I have a configuration where on some given move, the acceleration of XY is 1000 and acceleration of extruder is 2000. If I use M204 P1000, would such a move be slowed down?

Also what if pressure advance is enabled? Does M204 limit extruder acceleration which is used in PA?

bot

The extruder accelertation is basically always limited by the print acceleration, except for during retraction. The E axis simply does not need to accelerate as fast as X/Y when synchronized moves are taking place.

Only during retraction will the acceleration limit for the extruder come into play.

With pressure advance, extruder jerk is the more important setting. Asking for "more" pressure advance than a given E jerk value can "provide" will slow down the print.

M204 P1000 will slow down print moves, but not extruder-only moves. However, as you said you have X/Y accel set to 1000 anyway, M204 P1000 will basically do nothing but reinforce the already-set limit.

Khumarahn

@bot interesting. I use a long bowden (around 70cm) and use PA of around 2. And I can print flexibles with PA 16. I see the extruder working really hard, and it is the extruder jerk/acceleration that limits my print speeds, as I am not even close to the limits on XY.

Is extruder acceleration used at all in PA? If I have high PA and I use M204 P1000, would that limit the speed because of extruder acceleration?

Phaedrux

@Khumarahn said in Does M204 limit extruder acceleration?:

Is extruder acceleration used at all in PA? If I have high PA and I use M204 P1000, would that limit the speed because of extruder acceleration?

The extruder moves are generally so short extruder acceleration almost doesn't matter. Setting M204 P1000 will limit the XY acceleration, the extruder is likely already at full speed mere moments into the move. Extruder acceleration may come into play if XY acceleration was very very high.

What exactly are you trying to understand or resolve?

Khumarahn

@Phaedrux said in Does M204 limit extruder acceleration?:

The extruder moves are generally so short extruder acceleration almost doesn't matter.

I really don't feel this way. With higher PA it is extruder which is limiting print speed: XY acceleration limits simply do not matter any more.

My question is a simple curiosity: in situations where extruder accelerations are the limiting factor, does M204 command limit extruder accelerations as it limits XY accelerations? In principle this should be possible to understand from the source code.

Phaedrux

What is your retraction speed and extruder speed limit set to?

dc42

Extruder acceleration and especially extruder jerk limits do limit the printing speed when high values of PA are used.

Khumarahn

@dc42 said in Does M204 limit extruder acceleration?:

Extruder acceleration and especially extruder jerk limits do limit the printing speed when high values of PA are used.

Yay! I agree. Still, do you remember from the top of your head if M204 limits extruder acceleration? Or only XY?

Khumarahn

@Phaedrux said in Does M204 limit extruder acceleration?:

What is your retraction speed and extruder speed limit set to?

Here are my settings:

M566 X900 Y900 Z60 E1000:1000                      ; JERK (mm/min)
M203 X20000 Y20000 Z600 E15000:15000               ; MAX SPEED (mm/min)
M201 X3000 Y3000 Z125 E5000:5000                   ; MAX ACCELERATION (mm/s^2)
;M204 P2000 T3000                                   ; set print and travel accelerations
M204 T3000                                         ; print acceleration is limited by PA, except maybe extruder
                                                   ; would M204 P2000 limit extruder acceleration?

On another (but related) issue: I use voron mobius extruders, and they recommend extruder jerk of 8000. But I can't use more than 1000 because of skips. I don't understand what the problem might be.

Phaedrux

I would expect assembly issue with the Mobius or too low motor current. It shouldn't be skipping. Are you sure it's skipping and not just noisy?

Khumarahn

@Phaedrux I am quite sure it is skipping, I see it on the prints as underextrusion. I use the recommended motor with rated current 2A, and I run it at 1.6A. I assembled it carefully too.