Acceleration smoothness question

We are certainly not saying that you can't use those drives, they sound like great drives, and they will work perfectly well with linuxcnc. I believe that if you set the acceleration profile to only a small jerk limitation, and have the drives max acceleration a bit higher than the max defined in Linuxcnc, you will probably get very good results with them. The jerk limiting in the drive could take the edge of the accelerations of Linuxcnc without introducing a significant amount of following error, and the drive would quickly catch up to where it should be. You just may need to do a little experimentation to find the optimal settings.

Why does everyone freak out when they hear the words "following error". It is an ever present reality. The trick to tuning a machine is to minimize them while optimizing for best performance, and remaining within tolerances. It is always a balancing act of compromise.

Todd wrote:

We are certainly not saying that you can't use those drives, they sound like great drives, and they will work perfectly well with linuxcnc. I believe that if you set the acceleration profile to only a small jerk limitation, and have the drives max acceleration a bit higher than the max defined in Linuxcnc, you will probably get very good results with them. The jerk limiting in the drive could take the edge of the accelerations of Linuxcnc without introducing a significant amount of following error, and the drive would quickly catch up to where it should be. You just may need to do a little experimentation to find the optimal settings.

Why does everyone freak out when they hear the words "following error". It is an ever present reality. The trick to tuning a machine is to minimize them while optimizing for best performance, and remaining within tolerances. It is always a balancing act of compromise.

I feel the same way, these will be going on a lathe, if it were a mill it would be a lot easier to test the different settings on parts such as pockets or round bosses and check concentricity to see how the acceleration curves worked with multi axis interpolated moves. On a lathe it may be tougher. Perhaps threading would show an issue if started close enough to the start of the threads?

I know they will work if set to traditional acceleration values of 0 in the drive so I'm not concerned there. I just thought if it were possible to have the closed loop (motor to the drive) to ensure no lost steps as well as a smooth non jerky motion that would be a pretty phenomenal combination in a low cost stepper package. I suppose the real answer will come from testing which may be a few weeks while I get the lathe built. The machine is a 3 in 1 lathe mill all combo, so i suppose I can put the head back on and cut a few pockets and round (hopefully) bosses to see where everything winds up.
Chris

I suspect that anything you do in the drive that reduces jerk below what the drive can do
will increase the following error. That is, since LinuxCNCs planner uses infinite jerk
the actual following error peaks at the beginning and end of the acceleration will be larger,
the lower you set the jerk limit.

There might be some benefit if the jerk excited oscillations