85 lines
3.3 KiB
Markdown
85 lines
3.3 KiB
Markdown
# QuadMeUp Crossbow
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_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_
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# Current state
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Works:
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* Getting data from OpenTX radio using SBUS protocol
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* Transmitting 10 channels to RX modules
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* Frequency hopping
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* Getting basic telemetry from RX module
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* Sending 10 channels using SBUS to flight controller
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Needs implementation:
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* Binding
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* TX module configuration
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* Allowing to use OLED on TX to get basic data
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* RX configuration from TX module
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* Sending telemetry from TX to OpenTX radio
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# Protocol
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| Byte | Description | Notes |
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| ---- | ---- | ---- |
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| 1 | Frame type & used radio channel | bits 7-5 defines frame, bits 4-0 current radio channel |
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| 2 - 33 | Payload | lenghth defined by frame type |
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| payload length + 2 | CRC | using crc8_dvb_s2 method |
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## CRC
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CRC is computed using `crc8_dvb_s2` method. Initial CRC value for each frame CRC is equal to CRC of 4 bind bytes (unique for transmitter module).
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## Frame types
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| Value | Value hex | Description | Direction | Payload length |
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| ---- | ---- |---- | ---- | ---- |
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| 0000 | 0x0 | RC channels data `RC_DATA` | TX -> RX | 9 |
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| 0001 | 0x1 | Receiver health and basic telemetry `RX_HEALTH` | RX -> TX | 6 |
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| 0010 | 0x2 | Request receiver configuration | TX -> RX | no used |
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| 0011 | 0x3 | Receiver configuration | RX -> TX | no used |
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| 0100 | 0x4 | Set receiver configuration | TX -> RX | no used |
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| 0101 | 0x5 | PING frame, uses 9 byte payload | TX -> RX | 4 |
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| 0110 | 0x6 | PONG frame, the same payload as PING | RX -> TX | 4 |
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### `RC_DATA` frame format
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Protocol allows to send 10 RC channels in total encoded as following
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* channels 1 to 4 encoded using 10 bits each (5 bytes)
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* channels 5 to 6 encoded using 8 bits each (2 bytes)
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* channels 7 to 10 encoded using 4 bits per channel (2 bytes)
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Total length of `RC_DATA` payload is 9 bytes
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### `RX_HEALTH` frame format
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| Byte | Description |
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| ---- | ---- |
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| 1 | RX RSSI |
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| 2 | RX SNR |
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| 3 | RX supply volatage, sent in 0,1V |
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| 4 | RX analog input 1 sent in 0,1V |
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| 5 | RX analog input 2 sent in 0,1V |
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| 6 | Flags |
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#### Flags
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| Bit | Meaning |
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| ---- | ---- |
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| 00000001 | Device in Failsafe mode |
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### `PING` and `PONG` frames
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`PING` and `PONG` frames are to determine packet roundrip between **TX** and **RX** module.
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**TX** sends `PING` frame with curent `micros`. If **RX** receives `PING` frame, it respons
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its payload as `PONG` frame.
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# TX module connection diagram
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# RX module connection diagram
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