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!
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.
Thanks for the reply, Chris. Absolute altitude is not checked. No airspeed sensor. Do you think that having the APM2 unit completely enclosed in a fuselage could be preventing the barometric sensor from seeing changes in air pressure?
Is anyone using a nitro motor in conjunction with APM? -Thanks.....Tim
I'm sure others are using nitro motors, I've just never encountered them myself. You might want to check your logs and see what altitude it thought it was flying at.
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.
Thanks to all. I will try a faster cruise setting. I am glad to hear that having the apm2 unit inside a fuselage should not be an issue. -Tim
more of the same today. two more questions.
1. If I fly in manual mode and switch to auto, I assume it begins whatever mission is stored right? What happens if I switch to auto mode, fly for say 30 seconds and bail out to manual mode. If I continue flying and flip the switch back to auto mode, does the mission restart from the beginning or does it try to begin where it left off?
2. When starting in manual mode, what should the throttle be set at prior to switching to auto mode? I'm beginning to think that I need to put the throttle at its lowest setting prior to switching to auto mode. When I do that, switching into auto mode causes the throttle to increase (which is good), but after reaching a waypoint it begins to decrease again. (bad).
3. I'm really in the dark about downloading and reviewing the logs. I'd like to understand what altitude it thinks it is at during auto mode. Does the tlog contain this info? Is there a link to some documentation on downloading and reviewing mission logs?
As always, thanks for your help - Tim
sure could use some advice -
When you're airborne in manual mode, switch to auto, bail out after 30 seconds and switch back to manual mode, what happens if you switch back to auto after a while? Does it restart the mission or try to continue where it left off?
In manual mode, where should the throttle be set prior to switching to auto mode?
I wish I could help you, I'd like the answers too!
got an idea. In the mission planner, when you set the home position lat/long, how does the absolute altitude get filled in? Mine seems to show unusual values. Should this be set at the same altitude that you see higher-up in the right-hand panel when you move the mouse around? For example, my flying area shows a typical altitude of 358 m. I confirmed this with google maps and it seems to be the altitude above sea level. Should this be the absolute altitude for my home setting in the lower right-hand corner of the screen? Or should that value be zero, i.e. the reference point for ground-level altitude.
One more thing. The help dialog on setting the home position suggests hooking up the mission planner to the APM2 after power-up and gps lock at the flying field. Should I be doing that instead? I usually load the mission into the APM2 at home before leaving for the flying field.
Going to test this Saturday morning. Stay tuned. I will check this site before I leave in case anyone has a comment about this. -Tim
I'm new to this myself, but if I understand correctly...
Your airfield is 358m above sea level.
In the mission planner if you have "Absolute Altitude" checked then all your waypoints need to have a minimum altitude of 358. If you want the plane to be 50m off the ground you need to set the waypoints altitude to 408m.
If "Absolute Altitude" is not checked, then 0m is the altitude your plane was at when you turned on the APM. So for the same 50m off the ground waypoint, you'd set the altitude to 50m.
As you can see, problems arise if you are 358m above sea level, have "Absolute Altitude" checked and set a waypoint for 50m altitude.
No idea about hooking up the mission planner at the field. I'm going for my 2nd maiden attempt on Monday. (First one aborted with GPS issues)
Thanks for the reply Eddie. I understand the 'absolute altitude' checkbox. What I am asking about is the absolute altitude value that is in the lower right-hand corner of the mission planner screen, part of the home position setting. It seems to be asking for the absolute altitude of the home location. I do not know whether to put zero there or 358 there. I do not have the 'absolute altitude' checkbox checked. If you use notepad to look at the file that mission planner saves, the value that you put for the absolute altitude is in the first line of the file; it appears that line has the information regarding the home location; I see the same latitude and longitude values in that line of the file as I have for my home position. I tried both values (0 and 358) for the absolute altitude today and continue to have the same issue of the plane not maintaining altitude.
update for those who are interested. updated to the latest arduplane firmware (2.5). Flew Saturday 7/28/2012) Same issue when going into auto mode, engine goes to idle and loses altitude. I bailed out to manual mode, regained altitude, left the throttle at full high and re-enabled AUTO mode. The plane maintained altitude and airspeed and kept the throttle setting at an appropriate speed. The plane wanted to loiter around the launch point rather than going into the waypoints I had set. It did a good job of maintaining altitude and speed while loitering. This is why I would like to know what happens when (during the same flight) you switch from auto to manual and later back to auto. Does the autopilot try to continue where the mission left off; does it start over, or something else? Anyway it was more enjoyable this time out, still a lot to learn.