Another Jerk Question



  • I am now "commissioning" my 2nd Hypercube Evolution with a small build volume X 150 Y200 Z250. All motors and the Duet now operational.

    The X carriage is light with a Nimble, E3D & Volcano, 3 small 8mm linear bearings and some plastic. The Y mass includes the above plus 2 280mm x 8mm dia X rods, the Y carriages, & 2 long 10mm linear bearings - still fairly light but the X rods and Y bearings relatively much higher mass than the X carriage assembly. A heavy & rigid frame, and bed on 2 12mm Z rods.

    I am hoping this will print fast with PLA and the Volcano heat block - it will be fun finding out - for say rapid prototyping of small parts.

    My 2 questions:

    • 1: Can a Core XY have different Jerk and Acceleration settings for X and Y?

    • 2: Out of curiosity, how is Jerk implemented? Is a "large" pulse [ dependent on jerk and mass to be moved but limited by some stepper driver constraint although there would be no thermal issue for this time] sent to the motor to provide a steep acceleration ramp {before the normal acceleration} with the firmware planner function assuming it is instant?...

    • .......... and with the motor responding subject to its internal response rate and the printer responding subject to the elasticity of the X Y belts (in my case) and mass to be moved? and with some (undetectable! ) initial velocity oscillations about the standard acceleration ramp?


  • administrators

    @garis said in Another Jerk Question:

    1: Can a Core XY have different Jerk and Acceleration settings for X and Y?

    Yes.

    2: Out of curiosity, how is Jerk implemented? Is a "large" pulse [ dependent on jerk and mass to be moved but limited by some stepper driver constraint although there would be no thermal issue for this time] sent to the motor to provide a steep acceleration ramp {before the normal acceleration} with the firmware planner function assuming it is instant?...

    .......... and with the motor responding subject to its internal response rate and the printer responding subject to the elasticity of the X Y belts (in my case) and mass to be moved? and with some (undetectable! ) initial velocity oscillations about the standard acceleration ramp?

    The rate at which step pulses are sent to the motor is changed suddenly. Of course, the motor and the motion system cannot respond to this instantaneously; so there will be a temporary overshoot of the specified trajectory when the step pulse rate is reduced, and an undershoot when it is increased.


 

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