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Incorrect definition of jerk
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Nitpick. A jerk is an instantaneous acceleration change, not an instantaneous velocity change (that is acceleration). All the definitions are wrong in the jerk related tooltips.


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marcio created this task.Jun 27 2017, 3:31 PM
karrad assigned this task to efilenko.Jun 27 2017, 3:36 PM
karrad triaged this task as Low priority.
alexei added a subscriber: alexei.Jun 30 2017, 12:44 PM

@efilenko, this might help:
Distance = X = [mm]
Time = T = [s]
Velocity = V = dX/dT = [mm/s]
Acceleration = A = dV/dT = [mm/s^2]
Jerk = dA/dT = [mm/s^3]

@alexei, in physics you would be right. In 3d printing, you are not.
Jerk in this context should be seen as 3d printing jargon. AFAIK, in all known firmwares jerk is implemented as described in the tooltip.

Note that the unit is wrong in your fdmprinter.def.json. It should really be mm/s, not mm/s3 (even though the latter would be correct in physics)

alexei added a comment.Jul 7 2017, 9:11 AM

@fieldOfView , thanks for clarifying it.
So Jerk settings in cura is actually a velocity.
@efilenko: Could you check that the description is actually right and change the units of jerk to [mm/s] then?

@efilenko I can confirm that mm/s are the right units. This should be a simple change to make.

efilenko closed this task as Resolved.Sep 18 2017, 10:09 AM

Closing as per test team request