Hi! I was testing the prop rotation on my quad in my garage, with just enough throttle to hop along the ground a bit, and suddenly it launches up into the air. I didn’t increase the throttle or hit any switches. I pushed the throttle to 0 and nothing happened, so I switched off the controller to activate the failsafe. It took about ten seconds and dropped out of the air and hit the floor. Luckily, only the props broke and some bends is my frame (which I already ordered a new one) resulted from the crash. I don’t want to lose control like this again! What happened? Log is attached, Thanks!
At log line 1701, you can see APM enter RTL due to battery failsafe you configured to do that.
you got ECode 1: “battery voltage dropped below LOW_VOLT or total battery capacity used exceeded BATT_CAPACITY”
your RTL_ALT was 15meters, and APM planned to fly “back” - due to bad GPS inside, your position moved at least 15m between the time you got a fix, and when it got even more sats, and managed to get more accurate.
Lesson; do not allow RTL if you are indoors 
Thank you, it is definitely a learning experience.