Step-rate above 10kHz

[alainm]

I have a problem with 10kHz. If I change in stepper.cpp line 234, function calc_timer() from this:
else if(step_rate > 10000) { // If steprate > 10kHz >> step 2 times
to this
else if(step_rate > 20000) { // If steprate > 10kHz >> step 2 times
the problem goes away. So far I am sure that this is part of the problem...

As it is, the movement gets really weird. It is hard to describe, so I need help to understand what is happening at this point so that I can search a little more deeply. As far as I undestood, this produces 2 steps per IRQ, but are them uniformly spaced in time?

My printer has threaded screws instead of pulleys, so I have high step-rates. 10kHz is only 1905 mm/min. But this should not be an issue because Ultimaker is going faster then that...

[bkubicek]

the hardware is limited. The idea is to emulate having less microsteps. Its an imperfect solution.
Why don't you use less microsteps in general on this machine, you will have stronger acceleration.

[alainm]

In the time since that first message, I acquired a Ligic Analyzer and I can now see clearly what is happening.

I have changed that parameter up to 16000 and, surpringly, it worked just fine, with evenly distributed pulses.

I am already using only 1/2 steps, the problem is that I am using threaded screws for the movements and that gives me a too high mechanical reduction. In fact, there is a gap between possible implementations, belt gives too low resolution and screws give too high resolution, intermediate results are much more expensive.

I plan to move to full-steps in the future, that will reduce even more the requirements on the firmware and hopefully will allow me to achieve higher speeds. At the moment I have too much vibration to use that.

BTW, that multiple step implementation makes a lot of sense when using 1/16th steps, just not in my particular case (and some friends that are trying CNC machins for 3D printing)

I hope that this info can be usefull to someone else, but this issue could be considered closed...

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