Servers by jDrones

Airspeed reporting in MAVLINK

(Henry Wurzburg aka ATX_HELI) #1

Is airspeed reported via MAVLINK when no airspeed sensor is enabled? I know that it is continually computed by Arduplane even if no airspeed sensor is present as is wind speed and direction. The reason I ask, is that on my OSD, I can display wind speed, ground speed, but not airspeed…its always 0. This is Night-Ghost’s extended MinimOSD-Extra software. Perhaps its an error in his software…I am using a Pixhawk system.

MP shows non-zero wind speed, logs (NKF2) show zero wind speed
(Henry Wurzburg aka ATX_HELI) #2

Turns out that 3.8 added a param called ARSPD_TYPE, which if non-zero, makes the system think there really is a sensor and whatever it measures on that pin will be used…in my case 0. This would also make stall prevention non-functional, I think. Mission Planner provides no option for NO SENSOR currently, so you have to set this directly in the param. I have asked for a fix/enhancemet to make the default no sensor and provide that option in Mission Planner…

(tridge) #3

no, it only affects reporting unless you have ARSPD_USE set to 1
Flight control is completely unaffected if ARSPD_USE=0, which is the default

(Alexander Marinšek) #4

@hurzburg Maybe a bit off topic, but are you able to visualize the wind speed readings (logs) when flying without an airspeed sensor? I find, that I can only view real-time data in MP, but the logs NKF2.VWN NKF2.VWE are all zero.

(Hunt0r) #5

@Bannanna Yes, I believe your observation is supported by the code. Line 61 of AP_NavEKF2_Control.cpp suggests that not using airspeed inhibits the wind estimation.

Note that there seems to be an exception: If the code assumes the vehicle flies directly forward (no sideslip) then wind estimation is enabled, I think. Look into the assume_zero_sideslip() method, which is a mask for the fly_forward flag in AP_AHRS.

(Alexander Marinšek) #6

Yes, but is wind data logging in the case of wind estimation disabled? I can’t see any other reason, why MP would show the wind estimation, while the logs are all zero.

(Hunt0r) #7

Good question, I don’t know the answer but I’d like to know too. Does anyone know?

(Alexander Marinšek) #8

Judging by the fact that in the source code Ardupilot > libraries > GCS_MAVLink there are no handlers defined for the Wind message (#168) and since the wind speed in NKF2 & NKF7 logs are 0, I would assume the wind speed/direction observed in the mission planner was predicted by MP itself.

What’s your opinion?

(Hunt0r) #9

I’m out of my league here but… check out lines 2803 – 2835 in MissionPlanner/ExtLibs/ArduPilot/CurrentState.cs. I see what looks like a wind observer! If this is indeed running, I bet it’s where MP generates a wind estimate despite ArduPilot not providing it via MavLink.

Can anyone confirm/deny?