what is jerk?

[bkubicek]

max_xy_jerk. I tried to read the code, but still don't understand what it should do or what it should be configured to.
Just a question, not a problem.

[ErikZalm]

The g-code we use consists of many line segments.
When there is a curve it is made of line segments. These segments have a angle at the joining points.
We can only change the angle instantaneous if we allow a speedstep.
The max allowed speedstep is the jerk.

Sprinter and 5D also use a speedstep. But they only do it from standing still. It is proved that this is no problem.
Marlin (and grbl) allows a speedstep when there is movement. This allows high speeds when the angle between the g-code sections is not large.

The jerk is almost the same as startspeed in Sprinter. But also during movement.

On Sep 20, 2011, at 8:42 AM, bkubicek wrote:

max_xy_jerk. I tried to read the code, but still don't understand what it should do or what it should be configured to.
Just a question, not a problem.

Reply to this email directly or view it on GitHub:
https://github.com/ErikZalm/Marlin/issues/8

[bkubicek]

Aha, thanks. Thats a quite important concept that I was missing to understand the planning code. This also changes how the tuning process should be done.Not only trying to find a good balance between acceleration and velocity,the max velocity needs to sustain the wanted jerk.

From what I understand, the planner does planning for all moves stored in the buffer every time a new one is added? It sweeps forward and backward and calculates new speeds/accelerations. So, maybe stupid idea: If I know not only the next move but many future moves, I could look for a future travel move (no E) and slow down many moves before. This would decrease the overpressure in the nozzle, and then the travel move would not ooze so much. After, back to normal speed. The selection which moves to slow could be done by a "nozzle-relaxation-time", maybe also depending on the spring model.

[powtac]

Why is the Finnish translation connected to this (#8) issue?

[daid]

Nothing, but because the finnish translation came on my fork instead of the main branch it has a bit of an odd number, causing github to link the issues. Just ignore it.