Could use some help. My first test prints showed a heavily overextruded bottom layer (printed slowly). It's definitely not a matter of bed leveling, but I had the impression that the extruder more or less turned at the same speed anytime.
So I disassembled the extruder and let the stepper (a Sanmotion pancake, 200 steps/rev, 1A, 3.5V, 1:4 gear, 580 steps/mm) run without any load. It looks like there is a lowest possible speed. A G1 E10 F60 command (relative E) takes 9 sec which is more or less correct. G1 E10 F15 takes 18 sec, just like G1 E10 F30 ?? F values (for the E axis) between 40 and 1200 seem to perform well.
If I do the same with the z axis, everything is ok, I can go as slow as I want. Switching steppers or stepper drivers doesn't help. So it's not related to the board or the steppers.
In real life, when the extruder runs in FOLLOW mode, despite the higher F values for x/y, the required extruder speed is as slow as in my test case.
UPDATE: Looks like the test with "G1 E Fsomething" is misleading. Combined with a x/y move the e axis is as slow as required.