First I want to say that I hope I put this in the right category. Second this is not something I am going to do right away. Its probably going to be 6 months before I put this into action. Just planning now so I can get a good design down and get everything together.
What I have now is a modified X650F frame from hobbyking X650f.
By modified I mean I have installed longer arms on it. The total size at this moment is a little over 750mm. I am running 4114 330KV motors on it with Afro 30a ESC's. Pixhawk controls all of it.
So my plan is to purchase a second frame kit and use a few pieces out of the kit. Namely the Motor mounts and some of the different decks. My current configuration has the mounts flipped so they are on top of the arm. X8 Coxial would be accomplished by removing bottom esc plate and installing another motor mount. My plans for the few other pieces would be to make a battery platform underneath the mounting rails. Using some long standoffs to make the deck that will fit the batteries. Then I would install short mounting arms for a set of retracts. I could also add a deck for a companion for future projects.
I would use 4 more of the 4114 330kv motors for the bottom, What would be the prop I would want to use though. I am using 15x5.2 currently. Would I move to a 13x8 or what? How do you find out the optimal prop size for the lower prop? I am hoping for a formula or something other than buy a bunch and figure it out.
What are your guys thoughts on this. I could just buy another frame and do an octo I know that but it take the fun out of building something that is truly yours.