LinuxCNC S-Curve Accelerations

grandixximo wrote:

For example YangYang is now looking at stopping to destination with vel0 acc0 jerk0 all at the same time at the ends of an arc segment, in the servo-thread we compute next position forward in time, they keep adding up, and this leads to numerical errors, which make the jerk overshoot near the final destination, then you have to clamp down the error smoothly to arrive at destination, within current architecture you have to overshoot, you have to readjust, he has tried multiple avenues to fix this, nothing so far has worked.
How commercial TP fix this? they don't plan forward, they plan from destination backwards at each time increment with dedicated hardware, and deal with feed override changes by re-planning to a different time destination.
You can probably understand how different LinuxCNC is from commercial controllers, they practically work in the complete opposite way...
Many of the issues we are faced with, have similar kind of solutions in the commercial space, they just don't do it how LinuxCNC does it.
When I wrote "we are limited to what we can do", I intended it in the scope of implementing jerk limiting within the current TP, with tangential jerk limiting code that is being enabled with planner_type 1, and some blending and look-ahead improvements, to try and stick to jerk limited motion, without introducing any non-realtime code in servo-thread, sure a complete rewrite you can do whatever, but that is not something you do overnight. And we are also limited by physics, you can't have high-speed accuracy smoothness all at the same time, physics just don't allow this. I understand most here would sacrifice speed, but there is a camp that would like to squeeze out a bit more speed if possible sacrificing some accuracy within what's allowed by the gcode.




 

You'll need to change the TP. I'm not offering a $3000 cnc as a bounty for something you can vibe code overnight

Speaking of, a little bird told me that someone with the skills should request tormachs latest source....

DO IT NOW!