I am running a bixler with the Arduplane 2.28 firmware. Everything works pretty well, but I have been seeing a few strange issues with the reported altitude of the plane. The spot where I launch is 10m above sea level, but when I reload the home coords into the GCS after booting up the plane, I get anywhere from 8 - 22m reported.
Then when flying, I will set the altitude of the plane to 100m relative, but the altitude reported by the plane in the GCS is usually around 120m-140m, which is usually more than the home alt + 100m. The real altitude of the plane would be possibly around 70-80m based on my observations.
What kind of things affect the altitude reading? I know it is a combination of Barometer and GPS, but I'm not sure how exactly the interaction works. The interior of the plane can get quite warm from the ESC, would this fool the barometer into thinking it is higher up?
Any insights would be appreciated.
I'm not an arduplane expert (I deal more with arducopter) but I don't believe that GPS is used at all for altitude because it can be very inaccurate at times. I think it completely relies on the barometer.
The barometer has temperature compensation in the code but not sure really if that would cause issues.
The barometer on the APM2 is far better by the way.
Thanks Randy. I'll have to play around a bit more. I have another plane with another APM1 in it that doesn't seem to have the same problems. It runs much cooler inside, which is why I thought that might matter.
I will upgrade to APM2 in a few months when they are easier to get.
Temp. can affect alt. On a hot day your density alt will be much higher then the actual alt. Here in New Mexico we are at 4465 ft msl or above sea level, and on a warm day our density alt will be at over 7000ft msl. This will effect the Baro metric pressure and will cause the APM to shoe higher then what it is.
Just my 2 cents.
Does anyone know if you can adjust a parameter to correct this?
I have had the same problem and discovered the altitude varies depending on the speed of the aircraft. Basically i was pressurising the inside of the plane. I solved the problem by connecting the pressure sensor to the static line of the pitot
@ David- how can you connect the barometer on the APM2 to the static pitot? It's mounted on the board and do not think it has port connections.
I'd be interested to know how to do this. The APM1 also doesn't have direct pitot tube connections to the barometer, so I'm not sure how you would do it.
I think temp may have some bearing as Joseph said. We have had some very hot days here, sometimes over 40C, and on these days the home altitude seems to be even more offset (up to 30m when it should be 10m)