Safe? Depends on the math. Exciting? Sure could be! :black_eyed:
Need to add up the max amperage loads of everything you're looking to string together and make sure the wiring and connectors give you a decent safety margin so the magic smoke doesn't come out. There are folks in here much better able to give you advice in this area, but more details would be helpful - what props/motors/esc are you trying to use?
I will assume you mean in parallel.. as series would put you well over 100 volts and there would be spectacular and really dramatic happenings the instant you plug it in.
As far as motor wiring are you planning on full out 12 or 16 motors running or are you planning on 6 - 8 motors with redundancy for safety?
A lot more info would have to be put forth before any real answers could be given. Making 12 or 16 motors spin is easy.. controlling them is where the fun starts. How they will be used is a huge part in figuring that out.
Ease of setup depends on layout, two FCs tuned a little mushy on their own, would probably work well together on a counter rotating design with likelihood of other oddities; But only IF one controls upper, and the other controls lower, and you can change the direction that one of the flight controllers wants the motors turning in the settings. Or perhaps offset the rotational axis of one FC so all motors are in the same level plane, but still have to tune the flight controllersto wierd, and likely super low numbers.
I'm sure with enough messing around one could program a flight controller to do it alone, but I do not believe there are any with enough signal outputs, the poor tiny little processor on the board would probably be taxed.
I know for a fact that an Arduino can be home made for the set purpose you want, and little added weight. This can be used with the right firmware to then link with OpenFlight(?) or other software. I believe this last option is your most likely, as well as being the least plug-n-play.
4x6S LiPo in series is fine, whether you can attach it to anything however.. probably not.
Connecting batteries in series increases the voltage, 4 6S batteries is 100.8V fully charged. I doubt you are going to find multirotor ESC's or motors that can take that kind of voltage. Connecting batteries in parallel increases capacity, and therefor C rating, which is probably what you're after. It is possible to connect the ESC signal wires in parallel as well, both motors will get the same signal. This is only useful if the 2 motors are on the same arm.
ya, some suggest a Parallel hook up , other go for inter mesh while the more extreme is dual FCs well 12-16 motors are over redundancy but the point is to push as much lift as possible.
as for the FC I have options , NAZA Wookong or Lite , PX4 / Pixhawk , Or the humble Arduino with sensors attach on it. (not alot of my Fellow RC buddies are comfortable Flying the Big one on this) Reason Idunno