[blt]

Do you want to carry a payload or fly in wind? otherwise, I strongly recommend the Crazyflie, it is a good product with a vibrant community. It has an STM32F405 with FPU that is surprisingly powerful - nontrivial math in the fast control loop is no problem.

[ChuckMcM]

I have three of them :-) And I would like something with just a bit more payload. In particular I have been fascinated by the papers on cooperative work by multiple quad copters when driven by a supervising computer vision system.