2018-07-28 RFM69 radio module working (driver needs some polishing) + (1) ESC control ok
Bad luck, I started with a dead ESC (which I was convinced was working), and, since it was my first shot at PWM with ChibiOs, it took me a few hours to understand where the problem was exactly. However, it's working now. The 1st motor is a Turnigy DST 700. I'm using a Spider ESC for now, but I'm gonna get a few Blue Robotics Basic ESCs (they're working out of the box).
By the way, the DST 700 can only absorb 14.4V, while the solar panel can go as high as 21, so my plan is to use switching regulators (!) between the solar panel and the ESCs to lower the voltage to 12V. I just hope that regulators will degrade gracefully (that is, will output power with a lower voltage) when the voltage goes below 13V.