Once the main core of the electronics were installed and working, it was time to test and tune the speed and acceleration values.
First, the acceleration is set to a low value (750 mm/sec/sec) and then speed is gradually increased, testing each axis individually and also in concert with the others until the motors start stalling or missing steps. Another item that might limit max speed is if the ball screws start whipping.
With the Leadshine AM822 drivers, if the motors stall or lose steps the drive will set a fault and stop motion immediately. That makes it easy to detect when there is an issue and quickly find the maximum speeds.
In this case, the maximum speed on a single axis was 40000 mm/min or 1575 inches/minute (ipm). It was slightly less when driving X and Y together: 38000 mm/min (1500 ipm).
Here’s a quick video showing this maximum speed, which was achieved not only using a Raspberry Pi to control the machine, but operating the Pi wirelessly over remote desktop from a laptop computer. It’s possible it would have run faster with a NUC computer running LinuxCNC.
The next step in tuning is to slow the speed down to around 50-75% of the maximum and then find the maximum acceleration that can be used without faulting the drives.
The operational limits for maximum velocity and acceleration will be set significantly below the maximum to leave a safety buffer. On a machine this size, there is no need to ever go faster than 500-750 ipm for rapid moves. Most cutting feed rates will be under 350 inches per minute, based on the recommended cutting speed and chip loads for the material and tool being used.