Was landing and it stood up on two legs rolled over in its back, and continued to run. "A-B" combination didn't shut it down at first. I had to hit pause and then fly, after that the "A-B" combination shut it down. I lost one prop blade, one prop hub was loose, the other two prop hubs were beat up a little, and the blades had scratches. All four blades will be tossed out. Before removing the blades all four motors turned well. While taking the props off engine pod 4 must have had a little dirt fall between the housing and motor, It turned rough for a turn or so and the dirt seemed to flow through. I started the motors without the props on and tested, didn't notice any bearing noise. I am tempted to re-lubricated the bearings (What is good lub for this?) or replace the bearings (where do I get?) I sent in a crash report. Anyone think of something I may be missing?