Hello, new member. I have searched the site a lot about this without any luck. I'm using apm2 in a Great Planes Stick 60 airplane. The software version is very recent, no more than a week or so old ( you can assume early July 2012 version on everything). Stabilize mode seems to work fine. FBW A seems ok as well. My problem is with the achieving and maintaining the altitude settings in AUTO mode.
In auto mode the aircraft does not seem to attain the height it has been set for in the mission planner. When switched into auto mode the airplane does a shallow dive and the motor (nitro motor) throttles down to a very low idle setting. At that speed the airplane can barely maintain altitude and it is certainly not the altitude I have set it for..it flies at around 80 feet even though the mission is set for 200 feet for all legs. I have to bail out into manual mode after about 30 seconds to avoid a crash.
The APM2 is inside the airplane. Do you think that the barometer sensor is not able to make good readings or is there something else I should try? Should I consider using the GPM to control the altitude?
Any help or advice is greatly appreciated!
Replies
I am curious...is this still an open issue ?
http://code.google.com/p/ardupilot-mega/issues/detail?id=569
BEcause I had today the same phenomen:
With Airspeed-Sensor enabled (why would you otherwise want one ? Buy it, build it in and than discable it ???):
Manual, Stabilize, FBWA: All sweet.
Cruise: Immediately Speed up and pitch the plane down, needed to Switch back to prevent Crash.
Loiter: Starts to Speed up in faster and faster circles and loosing height.
RTL: I was today not brave enough to test this after I nearly lost the plane...
I will check throttle tomorrow for Auto...but it does not explain why I loose height so much. And I do not understand how throttle can be reversed for Auto and non-reversed for FBWA...
problem solved. throttle was reversed. I must have done 20 flights in auto mode with it reversed, trying to understand why the throttle was going as low as it could. Of course it did, it thought that it was increasing the power! In fairness, how else do you tell if your throttle is reversed? Before each flight, I check the airplane in stabilize mode to make sure the flight controls move the right way, but how do you check throttle? However, it was a real pleasure to see the plane fly its mission successfully this evening. Hope this helps someone. If you read my July 29th reply, now I'm not sure why the throttle seemed to work when it was loitering around the home position during that flight.
I have the same issue in my tests with APM 2.4, When goes to AUTO the engine (electric) goes to 0. I reset the APM several times until i get the desired answer on AUTO.
Tomorrow is the next test day. Should I update to 2.5 ?
Tim, last month I flew an APM2 in an 80" Cub with a Saito .56.
I don't think the issue is the nitro engine, as my 4 stroke probably shakes considerable more than your... well I assume you're using a 2 stroke? But that brings up the point, how well have you vibration damped the APM? I used my cheap and easy to make rubber hose dampers and they worked very well.
I think it's extremely unlikely that your fuselage is sealing out air pressure. Sealing out air pressure intentionally, is very difficult. The idea that you've accomplished it accidentally in a balsa box is a bit of a stretch.
I also had the similar experience as you. As soon as I switched to auto mode, it would throttle back and start falling. Well, it would start to pull up to maintain altitude, but it throttled back to an idle. I also had to take manual control back.
I'm not an expert in Arduplane, I just tried it one day. But I was told there are a few likely reasons:
1) An airspeed sensor would actually help.
2) The default Arduplane settings are more suited for a small, electric, slow, foam airplane. Most importantly, the target airspeed is too low. I can't remember what the settings were called, but have a look around. I remember one of them was something like "minimum throttle in cruise" or something like that. But really, the target airspeed is what we need to deal with, and I'm not sure how to do that. The issue is I think that my airplane happily cruises at 70-80km/h, but the default cruise speed is more like 40 km/h.
First, make sure Absolute Altitude isn't checked in the Mission Planner.
Second, are you using an airspeed sensor? If so, try disabling it.
I don't think the nitro engine is the issue, but I've never used one so I'm not sure.