Greetings All,
Just a couple of observations I made from a relatively recent waypoint mission of mine. The mission was impossibly long and SmartRTH was enabled. The vehicle returned safely to its start point with 13% power remaining.
First, the cruising speed for the mission was set to a rather leisurely 23mph. When SmartRTH kicked in, the quad maintained this speed throughout its 3.4 mile trek back to the home point. This might have been disastrous had the speed been even a bit lower.
Second, when SmartRTH engaged, the craft had been climbing sharply from 145ft to 300ft. The climb was aborted and the craft headed for home at 235ft AGL. It DID NOT climb to its set RTH altitude but maintained the altitude it happened to be at when SmartRTH took over. It wasn't a serious issue in this case but it would have been fatal for the quad had SmartRTH kicked in just a few seconds earlier at 145ft and the quad had taken the same route it went out on.
Just a couple of things to be aware of if you're relying on SmartRTH to keep your quad safe. It may not behave quite like you think it should.