arducopter flight problems

I built the a big heavy lift that I have been posting about on here using a Pixhawk. Before i put it in the air i wanted to experiment with something smaller so I built a hex with a ardupilot. 2212-920 motors multistar 20a slim and n8m gps. Got it in the air first try with just a lot of drifting in stable, althold and also in loiter. So I set channel 7 for trim set and proceeded to trim it out until it flew pretty steady in stable and althold. from alt hold I set it down and set trims, zeroed my rx trims. Then took off again. flew pretty steady. Put it in loiter and it started to fly strait up and no throttle control helped. So I flipped the RTL switch and it immediately shut down the motors and fell back to earth-at least it landed!! Probably 30-40 feet up.

    Ill ber putting it back together tonight; Not a lot of damage, just a couple of bent aluminum motor mounts but who knows what unseen damage is there.

Everything was balanced. 

I have been using Naza and P2 so this is my first apm/pixhawk and I want to learn it well before I try to but my big one in the air!

Any ideas? I did hear one or more of the motors race a little a couple times when I was re-positioning it while trimming. 

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  • Something else to check is how well protected your barometer is. I am assuming your pixhawk is still in its case, but even so, make sure it's out of the direct air flow of the props. With a bare board APM mini on a 250 quad I just put some foam over the barometer, but a loose fitting box may also help. Before using the foam I had the same issue as you in loiter.

    Are you using preset PIDs from mission planner or just defaults? I used the 3DR_QUAD_X4_RTF and they worked well. There should be some hex ones, too.

    • Had good gps signal. It did not go into rtl by itself. I did it when loiter started to fly off and the rel switch turned the motors off. 

      I set the hex presets. As I said it was flying fine and had it trimmed pretty steady in stabilize and alt hold. Just switched to loiter and it took off up so I tried to put it back in stable but it still went up, throttle down and it still went up so I centered the throttle and hit the rtl switch and thats when it fell out of the sky. Battery was at 12.4 on a 3s. 

      My failsafe is set to rtl not shut down and fall. 

      If the GPS was poor and it got kicked into RTL automatically it shouldn't shut off the motors??

      Thanks for the replys, I will check the failsafe again, I live in a wide open area with great gps signal, even in my basement I get a gps lock. 

      • How do you know your GPS was good? Just having a 3D lock is not good enough. Did you have telemetry showing your hdop was less than 2.0 at all times? Did you look at the logs for a failsafe RTL during loiter?

        Which failsafe is set to RTL?

        • Mike, you are correct--I don't know if there was a good lock. I do know that I always get good GPS on everything I use here in the boonies where I live, even my 20? year old garmin has less than 15' error .

             But I do know it was human error! I hooked everything back up today to check it out and found that the battery was at 9.6v?  I thought I had just put in a fresh 12.4v one on the hex. So it could have started a RTL battery failsafe when I panicked and  hit the RTL switch-which would make it do?!?!?!?!? I am putting it back together and will be getting it back in the air as soon as the weather breaks. I have never gotten into the logs yet but will tonight. I will have to read up on it and see how to access and read them. I do read want to be as proficient as possible and this is my first apm system! 

            The hdop--in the basement--10 minutes ago with it pouring rain outside was 2.1 with 9 sats and up on my porch right after, it was 1.4 with 12 sats. 

           If I have to worry about gps every time I take it out I don't think I could trust the system with my big Octo. I understand that things happen but it should not be something that keeps me from flying my machine for fear of fly off because my m8n gps does not keep good track of satellites. Never really worried about it with my naza's and p2's. Shouldn't have to with the Apm either.

          I have all fail-safes set for RTL. 

          • Glad you found it. It is easy to assume everything  was checked. Troubleshooting these complicated machines is not easy. The logs are really helpful and you can down load them in mission planner in te tabs under the HUD. Then MP has a built-in analyzer that will tell you a lot.

            Unfortunately GPS hdop can change constantly. The FC needs a much finer GPS signal that is commonly used for cars or hiking. I am going to Pixhawk controllers because they allow dual redundant GPS.

            I think Naza has so many fly-aways because they don't track GPS hdop adequately.

            Check out the parameters for each of the failsafes and what the options are when they are tripped.

            Remember that "normal" RTL it goes up to a height it hopes is above the trees before it returns. You can change the parameter for the height. But it always a surprise when it shoots straight up on your after a failsafe triggers an RTL.

            Well good luck.

  • If you do not have adequate GPS quality Arducopter has a failsafe that will kick you into RTL. Loiter depends on GPS quality. So you loose acceptable GPS lock, arducopter goes into RTL which causes the multirotor to go straight up to clear air for the path back to home. Many people misconstrue this to be a panic situation. There are parameters to tell arducopter what to do in case of various failsafes. Some of those options are to land immediately.

    PS> there are many other things that can cause a failsafe like low battery etc.

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