Discussions

Today I learned a lot, and I know that I likely made some stupid mistakes.  What was intended as a simple test flight, got way out of control, and had the potential to end very badly.  I am doing my best to dissect the logs, but I am still new with a lot of this. I would appreciate your help to figure out what went wrong and figure out what happened, and most importantly I want to learn from this and make sure it NEVER happens again.

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Let me give you some details on what happened….

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I recently completed a DJI 450 ARF build with a TBS Discovery Plate and a Pixhawk FC with GPS Module.  I spent months researching the build and decided on using the Pixhawk. I completed a few basic test flights in the backyard, keeping it eye level and just some basic movement.  Everything seemed in order despite more drifting then I had expected.  So, today I decided to take it to a local park to do another test flight.  The plan was to keep it under 15’, practice some basic flight movement and test out its stability.  I connected the battery, made sure it had a solid GPS lock, armed the copter and took off.  Everything was going as planned, it still wasn’t as stable as I had hoped but in stabilize it was fairly easy to control. Next I tested out loiter which performed pretty well, it didn’t hold position as well as the pixhawk videos online but it was decent.  Then I went to Alt Stabilize mode.  It seemed to have trouble maintaining a constant altitude, nothing crazy but drifting up and down 4’ or so.  Then, out of the blue it shot skyward! I watched in horror as it went straight up in the air, higher, higher and higher.  As you can see in the logs I immediately cut the throttle, but there was no result.  I then switch modes out of Alt Stabilize, I intended to switch to Stabilize but instead switched to Loiter.  Either way this did not have any effect. It still continued to clime, and then drift out of the area of the park and over houses!!  Then in what seemed like an eternity, I watched it start to fall from the sky. I tried switching modes and throttling up, but couldn’t do a thing except watch in horror as it came crashing down.  By the grace of God it landed in a tree in someones yard, and did not do damage to anything but itself.  I was able to quickly and easily find it from the beeping of the pixhawk.  All 4 props broke, one arm snapped, the GPS mast broke, lost the telemetry module and the rest of it is pretty banged up, BUT I have it, and that is the only damage that occurred. I ignorantly did not consider the risk of it throttling up and going skyward, I figured that if I went to  a local park kept it close and low I would be responsible and safe, boy was I wrong! 

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I downloaded the logs and have been trying to make heads and tails of them to figure out why this happened, and most importantly make sure it NEVER happens again. I know for sure I will have to go way farther out than a local suburban park for my next test flight.

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Here is a graph showing altitude, throttle in, throttle out, and mode. You can clearly see what I described above.  It shows that a failsafe fence kicked in, which I assume was the altitude and luckily i think that kept if from getting any higher