Minimum distance for accelerations

amimafe

Good morning,

I have a large format printer with DUET2 WIFI and we have noticed that when the models to be printed have many short distances the machine makes many accelerations and decelerations. Is there any way to configure duet not to accelerate or decelerate if there is no minimum printing distance?

Thank you!

T3P3Tony

@amimafe what yu are describing is common called "Jerk" (more properly instantaneous speed change" which you need to set to be correct for the mechanics of your machine:
https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m566-set-allowable-instantaneous-speed-change

amimafe

@T3P3Tony

Hello,

I have done a lot of tests to find the optimal Jerk setting but I can't find it.
I need that for closed angles like 45º the Jerk is lower to avoid abrupt speed changes and for more open angles like 160º-180º I don't apply the Jerk and continue at constant speed.

Is this possible? With meta commands this could be done?

Thanks!

T3P3Tony

@amimafe "Jerk" is supposed to be set to what the mechanics of your system can handle. Setting it too low and you will see deceleration and acceleration when going around a curve made up of sets of straight lines. Setting it too high and you will excessive shaking etc on corners.

What you describe as 160-180 degrees as "continue at constant speed", while more acute angles avoiding abrupt speed changes is what Jerk is used for. A single value does this because it sets the amount of change of velocity at a corner that is acceptable before acceleration needs to be applied.

If you think about the movement around a polygon approximating a circle, decomposed into X and Y elements this becomes clear, X and/or Y needs to change velocity at each corner of the polygon, even though speed remains constant. (velocity being speed & direction). So in order to keep speed constant, those (relatively) small changes in velocity need to happen "instantly" hence setting Jerk above the threshold.

Now if we keep making the polygon simpler and simpler until its a square, at this point there must be deceleration into the corners, and acceleration out of them for any reasonable print speed. Somewhere between the polygon with lots of sides (almost a circle) and a square, there will be a polygon with a corner angle where the mechanical performance of the machine at the set print speed makes "jerk" unacceptable, and acceleration and deceleration will have to occur.