Stall and airspeed parameter

hey guys,
I have recently played with airspeed for my arduplane. I noticed my plane behave differently when I set (previous setup was on default value) :

first try :
FBW_ARSPD_MIN = 50
FBW_ARSPD_MAX = 100
TRIM_ARSPD_CM = 6000
TRIM_THROTTLE = 50 (usually result 84kph true airspeed and 95 ardupilot airspeed)
USE_ARSPD = 0 (I didnt activate this yet so ardupilot will still uses my TRIM_THROTTLE instead of TRIM_ARSPD)

second try :
FBW_ARSPD_MIN = 50
FBW_ARSPD_MAX = 100
TRIM_ARSPD_CM = 6000
TRIM_THROTTLE = 50 (usually result 84kph true airspeed and 95 ardupilot airspeed)
USE_ARSPD = 1

I noticed that my FBWA is affected, I have much more limited roll and also limited pitch on landing approach(low throttle, about 30%), which didnt happen (or maybe it does happened but not as limited as now) when parameter above was still default. I assume this is due to the STAB_PITCH_DOWN parameter which takes control of my roll and pitch limit?

this brings me to a 2nd question, the ardupilot document stated that STAB_PITCH_DOWN is active when THROTTLE is below TRIM_THROTTLE, but does it also active when ardupilot calculated airspeed (not sensor speed) is below TRIM_AIRSPEED_CM?

ARSPD_FWB_MIN is in the units of m/s. TRIM_ARSPD_CM units are in the name of the parameter as cm/s. See the parameter list here. In Mission Planner there is also a column for units in the parameter list/tree.

What’s happened is that you are triggering the stall prevention feature which limits your roll when the measured airspeed is below ARSPD_FBW_MIN.

ah thanks for clearing it up! so stall prevention is not only triggered when throttle < TRIM_THROTTLE but also when synthetic airspeed < ARSPD_FBW_MIN ?

yes about the units, i set it correctly but wrote it here incorrectly, sorry, i will edit

Hi @SlickShot,

Maybe you still got mixed by the units? Above you mentioned

This gives 60m/s equals to 216kph. This is way faster than the expected speed of:

Hope this helps.

hehe yepp @VRquaeler … that was totally stupid me… I keep thinking in km/h… but anyway, regarding the trigger of the stall prevention, does it also check if airspeed < arspd_fbw_min && throttle < trim_throttle, or is it only triggered by throttle < trim_throttle? (assuming ARSPD_USE = 0)