QuadMeUp Crossbow is a DIY project that gives 5km (at least) of RC link for UAV (airplanes and drones) for a price below $40. I uses SX1278 (LoRa 868MHz/915MHz) compatible (like HopeRF RFM95W) radio modules connected to Arduino compatible boards. It can be regular Arduino connected via SPI to SX1278 or dedicated board like Adafruit Feather 32u4 RFM LoRa or LoRa32u4 II

Current state

Development, ready for testing

Protocol

Byte	Description	Notes
1	Channel ID	channel used for comunication between TX and RX
2	Frame type & Length	bits 7-5 defines frame, bits 4-0 payload length
3 - 34	Payload	32 bytes max
payload length + 3	CRC	using crc8_dvb_s2 method

Frame types

Value	Value hex	Description	Direction
0000	0x0	RC channels data `RC_DATA`	TX -> RX
0001	0x1	Receiver health and basic telemetry `RX_HEALTH`	RX -> TX
0010	0x2	Request receiver configuration	TX -> RX
0011	0x3	Receiver configuration	RX -> TX
0100	0x4	Set receiver configuration	TX -> RX
0101	0x5	PING frame, uses 9 byte payload	TX -> RX
0110	0x6	PONG frame, the same payload as PING	RX -> TX

`RC_DATA` frame format

Protocol allows to send 10 RC channels in total encoded as following

channels 1 to 4 encoded using 10 bits each (5 bytes)
channels 5 to 6 encoded using 8 bits each (2 bytes)
channels 7 to 10 encoded using 4 bits per channel (2 bytes)

Total length of RC_DATA payload is 9 bytes

`RX_HEALTH` frame format

Byte	Description
1	RX RSSI
2	RX SNR
3	RX supply volatage, sent in 0,1V
4	RX analog input 1 sent in 0,1V
5	RX analog input 2 sent in 0,1V
6	Flags

Flags

Bit	Meaning
00000001	Device in Failsafe mode

`PING` and `PONG` frames

PING and PONG frames are to determine packet roundrip between TX and RX module. TX sends PING frame with curent micros. If RX receives PING frame, it respons its payload as PONG frame.

RX module connection diagram

README.md

QuadMeUp Crossbow