You said yourself that you're new to this, so listen to people who aren't new to it.

You're going to drive yourself crazy troubleshooting this thing as long as you have voltage cutoff enabled. That may not be the entire problem, but it's part of the problem. NiMH and NiCad batteries don't need voltage cutoff -- in fact, they don't work properly if they are never drained completely. That's why good chargers have a NiMH discharge/recharge cycling mode, to rehab NiMH batteries that have sat around for too long.

The receiver and servo are not going to be damaged by undervolting if the battery gets too low. Why do you think they would be?