Add Gyro feature documentation

docs/hardware/gyro-receiver-mod.md

@@ -0,0 +1,134 @@
+---
+template: main.html
+description: A guide on how to add an IMU / gyro to an ExpressLRS receiver.
+---
+
+![Hardware-Banner](https://raw.githubusercontent.com/ExpressLRS/ExpressLRS-Hardware/master/img/hardware.png)
+
+## Overview
+
+ExpressLRS receivers that are equipped with an _inertial measurement unit_ (IMU) / gyro can provide stabilization for aircraft without a flight controller. See [Gyro](../software/gyro.md) for details.
+
+This guide explains how to attach a <abbr title="Do It Yourself">DIY</abbr> board to an existing receiver.
+
+## Supported hardware
+
+### IMU / gyro boards:
+
+- MPU6050: very common, supports 5V.
+- LSM6Dxx: not that common. Only supports 3.3V and will need a voltage regulator.
+
+### Receivers
+
+Any supported receiver based on the ESP32 chip, with an accessible I2C or SPI bus. Example: BetaFPV Super-P, RadioMaster ER6, ER8, even ER6GV (via PWM pins).
+
+??? Info "Finding supported ESP32 receivers. (click/tap to expand)"
+    In the [official targets list](https://github.com/ExpressLRS/Targets/blob/master/targets.json), the field `"platform": "esp32"` indicates that the receiver is based on an ESP32 chip.
+
+    If the receiver has PWM pins or multiple UART pads, those may be remapped as I2C or SPI pins.
+
+## Receiver configuration
+
+=== "WebUI"
+
+    TK
+
+=== "Target file"
+
+    TK
+
+## Wiring
+
+
+=== "I2C"
+
+    - The `SCL` pad on the <abbr title="Inertial Measurement Unit">IMU</abbr> board must be connected to the `SCL` pin on the receiver.
+    - The `SDA` pad on the <abbr title="Inertial Measurement Unit">IMU</abbr> board must be connected to the `SDA` pin on the receiver.
+    - The `VCC` pad on the <abbr title="Inertial Measurement Unit">IMU</abbr> board must be connected to a `+` pin on the receiver.
+    - The `GND` pad on the <abbr title="Inertial Measurement Unit">IMU</abbr> board must be connected to a `-` pin on the receiver.
+
+=== "SPI"
+
+    TK
+
+### Wiring examples
+
+<figure markdown>
+  ![TX Binding Tab](../assets/images/gyro/BetaFPV-Super-P-MPU6050.jpg)
+  <figcaption>BetaFPV Super-P with MPU6050 over I2C</figcaption>
+</figure>
+
+<figure markdown>
+  ![TX Binding Tab](../assets/images/gyro/RadioMaster-ER6GV-MPU6050.png)
+  <figcaption>RadioMaster ER6GV with MPU6050 over I2C via PWM pins</figcaption>
+</figure>
+
+## Testing
+
+=== "WebUI"
+
+    Start the WebUI on the receiver and go to the `Gyro` tab.
+
+    Image TK
+
+=== "Lua script"
+
+    TK
+
+=== "Serial console"
+
+    The IMU detection and gyro initialization is logged to the serial monitor.
+
+    1. Connect the receiver equipped with the IMU board to a computer, using an FTDI adapter (USB/Serial converter).
+    2. Open a serial monitor at 115200 baud.
+       Example: `sudo minicom --device /dev/ttyUSB0 --baudrate 115200`
+    3. Restart the receiver to capture the gyro initialization.
+       Example output:
+       ```
+         [...]
+         Starting wire on SCL 18, SDA 23
+         SPI: gpio_sck :-1, gpio_miso: -1, gpio_mosi: -1, gpio_nss: -1, gpio_int -1
+         Initializing PWM output: ch: 0, pin: 14
+         Initializing PWM output: ch: 0, pin: 1
+         Initializing PWM output: ch: 0, pin: 3
+         Initializing PWM output: ch: 3, pin: 15
+       > Starting I2C Gyro on SCL 2, SDA 4
+       > Detecting MPU6050 (Address 0x68)
+       > Gyro Id returned = 0x38
+       > Gyro Init
+       > Gyro Config Load
+       > Gyro Config: version 9
+         Detected baro: SPL06
+         UID=(11, 22, 33, 44, 55, 66) ModelId=255
+         Primary Domain ISM2G4, 80 channels, sync=40
+         Hal Init
+         SX1280 Reset
+         SX1280 Ready!
+         SX1280 Begin
+         RFAMP_hal Init
+         Use TX pin: 26
+         Read Vers sx1280 #1: 43447
+         Enabling DCDC regulator
+         SetPower: 21
+         Config LoRa hwTimer Init
+       > RxPratameters.registerParameters(): Setting up GYRO LUA
+       > RxPratameters.registerParameters(): GYRO LUA Done
+       > Gyro Start
+       > Gyro AHRS Start
+         [...]
+       ```
+
+    TK
+
+## Troubleshooting
+
+??? faq "If the gyro is enabled, why is status not OK?"
+    - Check the gyro [**orientation settings**](../software/gyro.md#orientation-settings), and [**level calibration**](../software/gyro.md#level-calibration).
+    - Check the [**endpoint calibration**](../software/gyro.md#endpoint-calibration).
+    - If using a <abbr title="Do It Yourself">DIY</abbr> board, check that it is connected to the correct I2C or SPI port. (Example: <abbr title="Do It Yourself">DIY</abbr> receivers with an integrated vario may use a distinct I2C bus for the vario and the gyro.)
+
+??? faq "Why do Aileron and Elevator functions seem coupled?"
+    In **Auto-Level** mode, assuming that sticks are centered, if the elevator moves when the aircraft banks, or the ailerons move when the aircraft pitches up or down, the physical **orientation** of the IMU might not be aligned on the aircraft axes of rotation. See known limitations in [Orientation settings](../software/gyro.md#orientation-settings).
+
+??? faq "Two PWM channels are not working!"
+    When the debugging options are used, the pins used by the debug UART are disconnected. Build the firmware again without the `-DDEBUG_LOG` or `-DDEBUG_RCVR_LINKSTATS` options.

docs/quick-start/webui.md

@@ -312,6 +312,10 @@ ExpressLRS 4.0 improves upon this with a new layout allowing for more sections o
     ![Import/Export Tab](../assets/images/webui/import-export.png)
     </figure>
 
+    ### Gyro Tab
+
+    This tab allows users to configure receivers with an _inertial measurement unit_ (IMU) / gyro to stabilize aircraft without a flight controller. See [Gyro](../software/gyro.md) for more information.
+
     ### WiFi Tab
 
     This tab lets you change the device' WiFi network connectivity and how it will behave when it is in WiFi mode.