I have been building a variable pitch tricopter and wanted to share my results so far.
Basically - I chose a tri and not a quad, because the tri geometry is the same as a traditional heli 120 deg swash plate. Since I can't write a firmware on my own, I wanted to use an off the self solution.
I used a home made simple frame
3 e-flite park 370 hollow shaft motors with their variable pitch props
3 castle ESCs that I had laying around.
Here is a picture of the motor and blades on rear arm