I starting to work on a new multicopter (quad, hexa, or octa) focused on achieveing longer flight times. I'm not expecting anything impossible, just curious what is the best combination of frame/motors/propellers/batteries that maximizes flight time. My payload will consist of the APM, normal sensors, a lightweight camera (less than 100g) on a lightweight 2-axis mount, and a couple extra circuit board about the same size and weight as the APM. Since I have a fairly small payload I could go with a quad design, but I'm assuming I could go hexa or octa and add more batteries. But the question is how much does this help the flight time, since you're adding a lot more weight, and possibly more motors, ESCs, etc. I suspect there is a point of diminishing returns, but where is that point?
More propellers help increase payload lift capacity, but at the cost of efficiency so you loose flight time. Large propellers has more efficient lift, but makes it harder to get stable flight. Higher voltage (6S) batteries are more energy/weight efficient, but low KV motors able to drive large propellers at that voltage are difficult to find and inefficient.
Not trying to scare you, but as you can see there is no fixed "ideal" solution to get long flight times. Experimentation IS required. :) Only thing I can tell you for sure is that less weight equals longer flight times.
Have you made any progress on this project? Looking for the same things only I need it to be able to lug around a giant camera if need be. I've only been able to find one site with the actually motor efficiency listed, I will give you the links to the 3 motors I was looking at, they are a little more pricy but since I'm going for efficiency I figured these we're probably close to the best.
but they look super efficient >75% at 5-15 amps, it says they can make about 30 oz of lift at 15 amps so I think most of the time they would be the butter zone but I'm not sure if I need more power than that? I assume mine would weight almost 4 Kg with the Cannon at that rate I need about 23.5 oz of lift per prop. They also have more powerful versions, does anyone know if the props they recommend can be used for a hexacopter? This subject is difficult to get help on.