over the last 5 years I had 2 quadcopter as a gift. the first one was basic, manual, I had to manually set the 4 motor speed for it not to crash during take off and I was alway controlling the amount of thrust myself.
1/ Why was that necessary? if you send the same thing to the 4 motor they should spin at the same rate and thus provide the same thrust no?
The second one was a smartphone controlled drone, you just hit the take off button and the thing fly and stay at the same place/altitute.
To do that I could see an ultrasonic sensor below the drone. if I made it fly above a mattress it would crash.
2/ Ok that nice but what about high altitude? what if my drone is hovering a 500m, what kind of sensor can I use to make him stay at the same place and altitude.
I already fiddled with GPS and I don't think it's fast/precise enought.