I tried storing the data in the interrupt handler and writing it to serial separately in the loop function. I had actually tried that before, but only with a very small buffer. This time I tried it with a 1kb buffer and it helped a lot to figure a few things out:
- the "7 0 " sequences are still there, but with enough consistency now that I've decided they are supposed to be there
- a data 'packet' is actually 25 bytes long, but a lot of the content seems to be fixed and never changes
- when moving the control sticks, the resulting control values now make perfect sense
- trim values are included in the packet
- there is a checksum byte in the packet calculated from all control values and trim values
- one byte of the packet seems to be a timer of sorts, it is always different between consecutive packets even when nothing else changes
- the first 194 bytes sent after turning the transmitter on is a fixed sequence of data
So after many hours of staring at a wall of numbers, some small progress has been made Now I'm kinda stuck again...
I have set up a second arduino as a master, and programmed it to send the same sequence of data as I got from the RC transmitter. Judging from the serial output from the slave arduino, the data it sees looks the same and it cannot tell the difference between the real transmitter and the master arduino. But unfortunately, when connecting the master arduino to the RF module, the heli just sits there and blinks, unable to detect any signal.
I must be missing something, still a lot more head-scratching to come with this I think...