We tried using an APM 2.5 as a flight data recorder in a Cessna 208B. It was built into a 3D printed box with own power supply and recording done on a mobile phone.
There is one problem though: When the aircraft is in a steady bank the APM HUD indicates horizontal attitude as the resultant g-load is downwards relative to the APM. The difference between APM indicated attitude and aircraft artificial horizon is shown below. (Aircraft AH indicates about 30deg LH bank in top right corner)
UPDATE: THE PROBLEM SEEMS TO BE THAT ARDUCOPTER CODE WAS LOADED AND IT WAS FLOWN AS DISARMED, INSTEAD OF USING ARDUPLANE - THANKS DEVELOPERS!
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I see droneshare identifies the vehicle as Arducopter. Maybe I had Arducopter code loaded - could that be the problem?
I just did my first upload to droneshare. Hope this link is sufficient for you to view the log file:
http://upload.droneshare.com/view/d4jk7xr
Could the high airspeed (around 100 knots) be the problem?
Hi Andrew,
Yes I have logs although it is quite a large file as the flight was about 2hrs. GPS velocity was correct I think, as it plots accurately in Google maps and I use a Ublox GPS. I can upload to droneshare if you are interested.
What wasn't accurate is the heading. It was only accurate until we did a 180 deg turn on the runway before take-off. Maybe I should have calibrated the compass again before flight. Still, I checked the portions during flight when the heading was correct and the roll was still incorrect.
HI Murray,
Do you have logs or at least the parameters you used?
If the GPS velocity information is correct then it should get correct attitude.
Cheers, Tridge
Hi Murray ,
i doing same test 1 years ago , the main problem found was the wrong roll info when plane doing turn in air ... centripetal force i thought that could produce that problem ... Now with new gps correction could be nice to understand if problem solved .
Right, as Pieter is implying, if you have a GPS connected it should use the change in velocity from the GPS to correct for centripetal forces like you're seeing here.
What you've done is a great test though! We tend to dry the APM/Pixhawk around in cars to test rather than Cessnas!
@Gisela & Joe: That is one of the reasons for this blog. I usually use arducopter code, but we loaded Arduplane on the APM (Some version current in November 2013). I'm not familiar with Arduplane, but am surprised to see this fundamental error and was wondering if someone else had noticed it?
@Pieter: yes, there is a GPS in the box and a battery that can be charged through USB.
Does this mean that the APM will show zero bank angle when a fixed wing UAV is circling a point of interest?
I do not believe the developers would make such a fundamental oversite.
The Nampilot
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