Last evening I took a late flight it was still light but would be fading within half an hours so I thought there was time for a 2O minute flight to a local hill I was about 1.3 km away when the FPV was breaking up quite badly and I was near the steep face on the left so I decided to climb to maximum height 120M and as I'd lost FPV I pulled home lock to fly home. In A brief flash of FPV I saw a grassy hill top approaching so I left to sticks to hover. Sadly it seems I did this too late as the last thing I saw was tumbling video. I drove to the hill and climbed in the fading light and with my FPV gear switch back on I picked up video from the gopro and was able to find it quickly I was relieved to see it all in one piece with no obvious damage to be seen but the motors were still running with the props stuck in the grass. On returning home I checked a local map and realised the hill was 121m higher than the take off point so it looks like I lucked out by a few feet as the quad was set to max out at 120M (400 ft) Today a spent time to check it over and recalibrate everything from scratch IMU, compass, RC alone and again through the Phantom. Then too a short flight. gimbal seems fine though it seems to be off level slightly but the flight and hover seemed a little erratic I had 10 satellites but the quad seemed to drift more than ever before and the blades seemed to out of balance to I changed them back to a set I'd used before a knew to be ok the next flight was quieter but the quad still drifted more while hovering than I'd experienced before. There seems to be more imbalance between the four motors so I suspect the time on its back has damaged one or more as the motors were still live when I picked it up last night and the motors sped up till I shut the battery off. I guess it was on its back like this for about 20 minutes before I found it So what are your thoughts? Is there anyway to confirm a faulty motor or are there other possible causes maybe a damaged gps? Though it does still report 10 or more satellites Any suggestions?