For those interested in using their multicopters to carry heavy objects you might be interested in the test that I performed today with Assistant Professor Nagatani-san of Tohoku university in Japan and Izu-san of EnRoute (a company that specialises mostly in Radio Controlled vehicles here in Japan and China).
Today was our first attempt at dropping one of the university's semi-autonomous rovers (2.5kg) from an ArduCopter equipped Zion Pro hexacopter (4.0kg not including the rover).
During the first try the copter was under manual control (stabilize mode) and the servo to drop the rover was activated by the tx/rx's channel 8 switch. I was the pilot and although we were all fully expecting the copter to climb I was still surprised by the speed of the leap into the air and I couldn't keep the throttle low enough without cutting the engines completely. You can see the disasterous result 44 seconds in.
The final test (1:24) was back again with the rover but this time using alt-hold and you can see how much better the new 2.9.1 Alt-Hold is than a human pilot (or at least this human pilot!) with the copter only climbing about 10cm or so.
So the moral of the story is sometimes it's best to trust the autopilot.