Octocopter trouble.....………Please help !!!!
 

I am planning a 16 rotor Octocopter with contra-rotating setup for each arm. I plan to do thisby fixing one motor prop CW in normal orientation and another motor prop CCW in upside down orientation in each arm. Is it feasible ?? I plan to have separate ESC and battery for each of the motorsbut can I connect 2 ESCs of each contra-rotating setup of each arm into a single plug of the flight controller essentially fooling it to believe the contra-rotating setup as a single motor propconfiguration making the whole setup a basic octocopter. Please comment on the feasibility of the idea !!!

I'm probably overstepping my KSAs here; my experience with multicopters is limited to a couple of toy-style little quads. But it's been a couple of days.

As I understand them the controllers for multicopters take the rotational torque of the props into consideration, and in fact rely on it. That's one reason they require both CW and CCW rotations on alternate arms. So it probably isn't necessary to use contra-rotating props on each arm, and may in fact not work well (that's where I'm guessing.) Would love to see what you build.

That brings up another issue- how are you going to control it? The setups that are possible are limited by the programming in the controller board. In the early days when builders just used a HH gyro on each arm to keep the vehicles stable you could do whatever you wanted, but those machines didn't fly nearly as well as those with the dedicated controller boards do. Then the other obvious issue is why? Y8 setups are so stable that there doesn't seem to be a need to move beyond that. You are adding considerable complexity to an already complex machine. That makes for 16 sets of connections that need to be checked, 16 props to inspect for damage and keep tight, 16 sets of motor bolts to vibrate loose, 16 motors to vibrate and play havoc with your controller board, and so on. If a currently produced Y8 setup isn't going to meet your needs, maybe it's time to start looking at the high end single rotor type aerial photography platforms?

Now, why 16 connections ?? I want to generate maximum thrust from the smallest possible setup and a contra-rotating setup provides the maximum thrust possible. Moreover, I experiment a lot with quadrotor or octorotor types so wanted to try out the new configuration. If this is succesfull I will build a 16 rotor with about 180kg of thrust and an hour of flight time to carry a person with it.

Actually, the counter rotating props make less thrust than a flat multi rotor machine. And going with more rotors means going bigger, not smaller. If the goal is to get the most weight carrying ability with the smallest vehicle, a quad with really big props would be the way to go. As for making a man carrying vehicle, you might want to look into the FAA certification procedures for making such a contraption legal. I think you'll find that past experience in experimental aviation has convinced them that backyard tinkerers shan't be allowed to bring a crazy new idea to fruition without a significant amount of research and testing. Of course, if you have a Ph.D in aeronautical engineering and a couple million dollars in grant money, I don't see why you shouldn't give it a try.

I'm with Jester and Alan on this one... in particular, the counter rotating props aren't going to work.
specifically, all multi rotor aircraft depend on the torque produced to make the vehicle yaw.
you'd need to set it up so that both props on a particular arm spin in the same direction.
with no motors producing usable torque, you'll have no way of controlling yaw.

Actually Jim, the coaxial setups do work fine. There are Y6 and Y8 setups that have coaxial props on 3 and 4 arms. I don't know how they handle torque though. The Y8 setups can do it the same way a quad does. Maybe the Y6 ones have the tops and bottoms spinning in different directions? The value of the Y setup opposed to the flat setup is better wind handling. Pilots accept that there is a small weight capacity loss (can be a considerable loss if the right prop combinations aren't chosen) in exchange for the better stability.

ah... you're exactly right Jester (as usual I might add ;) ) did a little research during lunch...
I knew there are coaxial multi rotor aircraft out there now, I had ASSUMED ( :D ) both props on a given axis rotated the same way, but it turns out they are typically counter rotating.
yaw control is handled by speeding up or slowing down ONE of the two motors on a given axis... so they do work exactly like a traditional multi copter,
except for yaw control.
that does add another layer of complexity ;)