Ramps, 5 stepperdriver grbl and a lot error 25 at high feedrates

hello out there

If you always get error 25 at grbl and in different lines although the gcode looks good, read on …

I have equipped my ramps board with 5 stepperdrivers because i can :wink:
and I didn’t want to solder the motors in series

My config:
Arduino mega clone with 16u2-chip, ramps 1.4 shield, 5x DRV8825 @ 0,9V, 5x nema17_2A_59Ncm
and 12V - 12.5A PSU
firmware: grbl-mega-5x from fra589

After 2 weeks of troubleshooting, I have now discovered and corrected the error!

I’ve worked with feeds 1000mm/min so far.
I constantly got the error 25 (wrong gcode in line: …) via grbl at cncjs

But The gcode syntax was ok!
Whenever I restart -with the same gcode- the error came randomly in another line!
WTF !?

I have grounded my cables, renewed arduino, reading unsuccessful hours over hours in forums. nothing nearly with my prob! electrical noises, bufferoverflows, usb-errors nor lasers from aliens
I wanted to see the error in more detail and switched down a gear, feedoverride at beginning to 50%
and the errors was suddenly gone

Microstepping too high!
Ryan recommends a microstepping of 32 for the mpcnc. If (like 99%) the 2 motors of each axis are wired in series and you end up working with 3 stepperdrivers, do it.
With my 5 drivers the arduino calculations simply overwhelmed with feed rates higher than 600-700mm/min and the strange errors say hello.
with 500mm / min it was still possible

I hope my observation can help one or the other.

Greetings, CU