time printing estimation

[Food24 0]

Hi all,

usually estimated time from CURA is greater than the actual time due to ecceleration and jerk factor.

But, it is possible the contrary ? it is possible that actual time is lower than the estimated one ?

For instance if jerk is 20 mm/s (default acceleration is 50 mm/s) and i'm printing at print speed of 11 mm/s, could be possible that my printer moves faster than the estimated behaviour ?

Thank all.

FOod 24

[robinmdh 100]

No, since acceleration is taken into account and jerk as well actually (part of marlins motion planning is just ran on all the movements to calculate all that so I'd be surprised if jerk was removed from that checked with Tim(bagelorb)), the time estimates are within about 1~5% of error margin (for typical prints) except when heating up or cooling down printcores, as far as we've seen with the UM3.

The thing that's not taken into account is the weird little rounding errors and things that are actually bugs in marlin.

If you use a non marlin printer time estimates might be off more.

Does this information make you happy?

Edited May 1, 2017 by Guest

[Food24 0]

I'm using a printer WASP, mod. Delta 2040 . I use Marlin firmware. Also my object is a n.10 faces-pyramid with a base of 29x29 mm and an height of 22 mm.

Something is not clear for me:

The jerk specifies the istantaneous rate reached from the printer before acceleration. Practically, jerk works when chaging speed or direction.

If the jer is 20mm/s and i'm working with a speed rate of 11.2 mm/s this means that the printer istantaneously reach 20 mm/s. If so there are two possibilities: 1. the printer decelerates from 20 to 11.2 mm/s; 2. the printer will move faster than expected behaviour.

In my test when I print at 11.2 mm/s I have an actual printing time of 152 s while the estimated time is of 240s.

What could be the reason ?

Food24

[robinmdh 100]

In your case the printer accelerates instantly* from 0mm/s to the maximum of 11.2 mm/s or decelerates instantly* to 0.

However remember that marlins jerk implementation is not exactly correct and is only applied to/from standstill, if I remember correctly.

Given that cura's time prediction was based on A version of marlin things might have changed on your machine so that might explain it...

Have a look here and compare that to your marlins plan_buffer_line function (in planner.cpp) if you really want to know.

And as I said there are bugs in marlin, both the main marlin and the ultimaker marlin...

*: instantly reach a speed is obviously mechanically and physically impossible but to the software it pretty much is what happens.

Edited May 2, 2017 by Guest