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.
Yes, you should be able to use AltHold mode indoors with a sonar and it should work ok. There are some improvements to sonar based alt-hold in AC3.1. That’s not out officially yet but you can test the release candidate by going to the mission planner’s Firmware screen and clicking on the Beta firmwares link. Just be careful 'cuz it hasn’t completed testing yet.
Alternatively you can wait a few weeks for the official release.
Thanks for the response. I have another question regarding the altitude reported in the flight data tab of the mission planner. Is that value from the sonar, barometer, inertial measurements, or a combination of the three?
For example, I can stabilize my quad in the rig I constructed and the altitude continuously climbs even though it is actually not ascending. I believe this is caused by noise in the inertial calculations, but at that low altitude of 2-3 feet wouldn’t the sonar sensor override other altitude measurements?