Yep, you can do a quadcopter on an 18F chip with PBP. I found this question in a post from a long time ago, but that thread is now closed. I'd been working a quadcopter on and off for maybe the past year and a half and finally got it all put together. It's obviously not as sleek as most of the commercial drones out there, but my main goal wasn't really aesthetics. I'm in the process of tweaking controller gains to make it more stable.

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All the piece parts were under $4 (including the custom PCB) except for the RC receiver (12$). Most of the structure is just 3D printed PLA or homemade carbon fiber parts (center plate and arms).

It runs a 200Hz complimentary filter at 64Mhz and the program code is just under 18k, although there's some fat in the code I could cut out and make more efficient. I'll go out on a limb and say that I think you could do a drone on a higher-end 16F chip if you left off the magnetometer and/or went with a 100Hz filter (if it didn't affect controllability).

Also a big thanks to Darrel Taylor. I didn't know him, but his instant interrupt contributions were invaluable to getting all the functionality needed to service the RC receiver inputs and the motor duty cycles. I can also tell from his posts he was generous with his knowledge and time to help others.

Dave