Michael Dunn @ edn.com did a quick tear-down of his drone.
The main processor is an ST STM32F031K6, an ARM Cortex-M0 with the usual cadre of peripherals, as well as a motor-control block (the leftmost large chip in Figure 2). Although at the lower end of the ARM continuum, it’s doubtless more than powerful enough for this application. Amazing what $1 will buy you in a microcontroller these days.
FPV drone teardown – [Link]