Today, I went to an un-named city park in Campbell, CA. with my 16" prop monster quadcopter.
I had previously programmed in some waypoints that would cause it to make a circle around the park.
So, I armed the craft, and gave the throttle a little 'nudge'. It took off just as expected and went straight up to the programmed altitude of 60'. Then it took off at full speed in the WRONG direction! The park is ringed by trees, and by the time I could get the remote set to MANUAL, the craft had hit the top of a tree. It then fell about 20 feet through the branches and got stuck!
I tried to re-arm the craft in an attempt to have the motors break it free, but I saw no movement - either it wouldn't arm because it wasn't level, or else none of the motors could freely turn. Brushless motors of the type used in aircraft have very low starting torque.
My toy was stuck WAY up in a tree that had lots of small branches. Even if I could climb the tree (hard, because there were no branches below the 15' level), I couldn't get far enough out on a limb to grab my toy.
So, I went to Home Depot and bought a 100' length of clotheline and a large, heavy steel hook (the type you normally screw into wood). I wrapped the cord around the lag-screw end of the hook and tied it tightly. I went back to the park and started throwing the hook up into the branches. I first thought that if I broke it free, I would try to run underneath it and catch my precious toy, but decided against it. It weighs about 5 lbs, and has lots of sharp edges. A 40' fall would give it enough velocity (if it didn't get slowed by the branches on the way down) to do some real damage. So I decided to let if fall to the ground if I could break it free.
I am not the best when it comes to throwing hooks into the air, and getting it that high took some real force. Several times, I caught branches with the hook that were almost too big to break by pulling on the rope. In that case, I would have to leave my hook in place and try another method. Fortunately, I got the hook back every time. After about 10 minutes of trying, I hooked on to the branch very near the quadcopter and gave a hard pull. The craft broke free and fell to the sidewalk under the tree. It hit on one arm VERY hard.
Inspection shows that I bent one of the 4 arms - only. My construction technique of using 13mm thinwall square aluminum tubing stuffed with a 7/16" hardwood dowel proved itself. The arm was bent and the dowel inside was broken, and there was a crack in one of the plastic brackets, but virtually nothing else was damaged!
I don't like to leave things broken for long, and I had another length of 13mm square tubing and another length of dowel. I printed a new plastic bracket, and put the craft back together. Now, 2 hours later, it is ready to fly again!.
So why did it take off in the wrong direction?
I checked my setups and realized that there was no "waypoint #1 OR "takeoff point", only waypoints 2, 3, 4, & 5. I don't know how that happened, or exactly what effect that would have, but right now, that is the only explanation I can think of.