Can you please verify that altitude hold with the recommended MaxBotix XL-EZ4 sonar sensor should work indoors without a GPS lock. Everything I have researched including the source code implies that it should (I think).
I have an APM 2.5 with firmware version ArduCopter 3.0.1.
This is the situation. I have recently installed the sonar sensor and tested it outside in altitude hold mode. I tried the application of flying it over a trashcan to see it auto correct the altitude change. It registered a change, but reacted so strongly that my quadcopter crashed. I know this can be fixed by tuning certain gains. I have constructed a rig that I connect the quadcopter to indoors so that I can tune gains without fear of crashing if I tune incorrectly. However, so far indoors it seems that the sonar sensor is not reacting properly. I can arm the quad, begin to hover, switch to altitude hold mode, and pass something under the sonar sensor and there is no reaction. This is what makes me wonder if the GPS lock is necessary even though I know it should not be for the barometer/sonar readings.