Hi guys!
Last time I had a chance to work a bit with different ESCs flashed
with SimonK firmware and since it wasn't really plug and play or fast
and furious as most comments in web say - wanted to share some
experience.
First of all I tried 3 different rotorcrafts with 3 different motor
sizes with 3 different ESCs:
ST4708 360KV with 15x5.5 propeller and Turnigy Multistar 45 Amp 6S LiPo
MK3638 700Kv with 13x4.7 propeller and ZTW Spider Series 30A OPTO 4S LiPo
CF2822 1200Kv with 10x4.7 propeller and Afro ESC 12Amp 3S LiPo
As far as the first rotorcraft was pretty large, it was pretty stable
and I didn't really noticed any weird behavior.
However both other showed very weird frame oscillations mostly in
horizontal frame positions. And there was no PID combination to find,
that would remove these oscillations (was using ahrs_int_cmpl_quat
with euler_int attitude stabilization).
The oscillations wasn't really large, didn't really impact horizontal
position stability but the overall external flight quality was
unacceptable.
The actual problem eventually was in SimonK firmware. Most of recently
released versions (well, most likely ALL available to buy ESCs with
SimonK firmware) have a poorly solved max output power limitation
depending on commutation period (most probably because of atmega's
calculation power lack). That is why on some motor/propeller/pwm
command combinations it doesn't give enough power to motor, causing
undershoot and therefore the weird oscillations I described.
The actual solution was to increase TIMING_RANGE1 and TIMING_RANGE2
values, so the firmware can give more power on lower rpms. But it
should be care taken about that modification, because it can cause
other problems, for example motor stall.
P.S.
Right now there is an other way of the max power limitation
implemented under the tgy github, looks like it should work more
stable on different motors/props/rpms than before.
Best Regards,
Sergey
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