Tiny Quadcopter (Part 4)

I've got the two radios talking to each other, and I've written a trivial implementation of sumd, which I haven't tested yet. See https://github.com/davidji/rust-rc

A bunch more stuff has arrived in the post, including:

  • Tiny form factor NRF24L01+ modules, w/o LNA
  • Combined Arduino Nano NRF24L01+ boards

This is rather quicker than I expected, which makes me regret cobbling together an STM32F4 board, NRF24L01+ with LNA and buck boost converter.

The trouble with the STM32F4 board is it's too long for the quadcopter frame. More annoyingly, so is the combined Arduino board. It's probably time to go back to the Arduino pro micro with Tiny NRF24L01+ module and LDO regulator.

It would be interesting to know, when considering the energy efficiency of various things I might put on a quadcopter, how much power the quadcopter needs to hover and how that relates to it's weight. It's pretty likely that almost all the power goes to hovering, and weight is very important.

This article goes into the physics:

https://www.wired.com/story/the-physics-of-why-bigger-drones-can-fly-longer/

but if I just assume a flight time of 5 mins or so, on a 500mAh battery, then it's about 6A * 4V = 24W, and that is proportional to weight, and the weight is about 50g, that works out to 500mW/g.

So something that weights an extra 1g needs to save 125mA to be worth it. The  buck boost converter I used doesn't satisfy that requirement. Also, it's the LNA in the NRF24L01+ module I'm using, which draws up to 120mA that means I need the buck/boost converter at all, so it's expensive too.

So everything points towards the Arduino pro micro. It might even be possible to program it in Rust, via the avr-hal crate.

I had a bit of a go at using avr-hal, which looks promising, but compiling rust for AVR takes quite a lot of setting: It's a fork of rust. It doesn't seem like its far away, however if the transmitter sends sumd packets I could just write a sketch to dump the packets as they arrive onto the serial port, so it's not much code.

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