roteron If you are interested in lomg term flights you might want to have a look at MADcomponents. The MAD5008 weights just 130 g and can swing a 24“ prop with ease. The MAD5010 can do even more at a weight of just 150 g.
Yesterday „Possi“ who lives near my home broke his own world record using those motors - 190:06 mins with a single charge.
As it comes to the double-tricopter it just looks a bit like a conventional quad. A quad-p or quad-x has props spinning in one direction on one axis and props spinning the opposite direction on the other axis.
My concept depends on big main rotors generating all the lift and two small rotors which add control. So the cg has to be between the main rotors. If i would build it like a quad, two small propellers would have to cancel out the torque of two large rotors.
So if going the conventional way i would have to scale all of the rotors to the same or at least similar size.
I previously built a quadcopter with big main rotors, small tail rotors and the CG moved almost complete to the front.
My fault was to expect this to work on a tricopter too. The previous built quad is variable pitch so it can provide negative thrust. The tricopter cant so it needs gravity to stabilize itself.