RE: initial movement speed crashing Z axis
Oldish discussion but if someone has difficulty with this....
After updated PrusaSlicer (2.2 to 2.3.1) and Marlin firmware (1.0 rc7 to 1.1.9.1) on my Prusa i3 I still had the same issue as described.
Came across this which clears the units question up (as hypothesed by @all-registers).
- `M203` commands are in mm/second
- 'GO` and `G1` commands are in mm/min
This is good to know, but not my actual root problem. In my case, it was knowing the feed rate my printer is actually capable of before choking! (Z-axis here, but could also manifest in other axes I suspect)
In the default Marlin 1.1.9 Configuration.h file the Max Z feed-rate is 5mm/sec (or 300mm/minute). I had kept this, thinking it seemed reasonable....but it actually reasonably quick/demanding for screw-drive system.
To show this, if I actually try things at this limit with the correct units, `G0 Z5 F300` my printer chokes - it can't (and never could) actually achieve its max feed rate. The issue has just been hidden.
So the PrusaSlicer apparently-offending `G1 Z5 F7800` does get corrected by the firmware (to F300) but this still causes the z-axis motors to get upset.
My Solution: lower the max rate either in the firmware and/or in PrusaSlicer (so an M203 is issued) to an achievable figure, e.g.:
m203 z2 #... 2 mm/sec , or 120mm/minute.
Sending 'G1 z5 f7800' should now be throttled to 120mm/min 😊