# Velocity/Acceleration settings for smooth motion

01 Jun 2018 19:54 #111409 by Cpk_Rbt
According to the INI documentation , MAX_VELOCITY is given in machine units per SECOND (as opposed to feedrate, which is machine units per minute).

We have a 6-axis trivial kinematics machine with MAX_VELOCITY set between 175 and 360 for each axis (different speed limits due to gearbox RPM ratings). MAX_ACCELERATION for each axis is 4x the MAX_VELOCITY for that axis.

With these settings, our motion is fairly smooth, however, we noticed that when we set the settings higher than this, the axes jitter and shake during motion.

First off, these numbers seem really high! I'm somewhat of a newbie when it comes to mechanical things, and I was just looking for some guidance if we're on the right track with the values we've chosen. We tried to set the velocity/accel limits based on what each gearbox can handle for a constant/peak RPM (which was a lot of unit conversions to get from rotations per minute to degrees per second.)

01 Jun 2018 21:56 #111416
Where did that 4X come from ? For the 360 mm/s velocity ( that is 21.6 meters per minute ) you get acceleration of 1440mm/s/s, and that is way to high of an acceleration for a machine that has to move anything heavy.
I do have some small machines set at 5000 acceleration, but the total mass of moving parts is under 4 KG.
You should set acceleration depending on mass, not velocity, so the heaviest axis would have slowest acceleration and the lightest one should have the fastest acceleration, even then i would not suggest going over 750 for the lightest axis. It is all good and dandy when you move in one direction, but can they handle changing direction at full velocity with that type of acceleration?
If the machine can handle that, test it by doing quick short moves in one direction and see how much it jerks and lower the value as you see fit.
Regards,
Tom