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Trainer (Head Tracking) Input

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Overview

The ExpressLRS TX backpack has the ability to receive channel data from external sources/backpacks e.g. the HDZero VRX backpack. This channel data can be sent back to EdgeTX as trainer inputs, which can then be mixed into output channels or can be configured to directly override channels before they are sent to a receiver.

Requirements

  • ExpressLRS V4 (minimum)
  • TX Backpack 1.5.2 or later
  • EdgeTX 2.11 or later

Handset Setup

In the ExpressLRS Lua script, go to the select the "> Backpack" menu entry

Backpack menu entry

Ensure the Backpack is turned on

Backpack enabled

Scroll down to "HT Enable" and set this to "On"

HT Enable

Direct Channel Output

As mentioned above ExpressLRS can override channels directly being sent to the receiver. To achieve this, set the "HT Start Channel" to a value from "Aux1" to "Aux10".

HT Start Aux6

As an example if you choose AUX6 then the channel overrides will be channels 10 upwards, depending on the number of channels sent via the backpack. The HDZero goggles output 3 channels for a Pan/Tilt/Roll head tracker so if "Aux6" is selected for the "HT Start Channel", channels 10, 11, & 12 will be overridden when sent to the receiver.

NOTE

It is important to remember that if you must also select a packet rate and switch mode that will actually send all the channels you need to the receiver. e.g if you are selecting "Aux6" then you will need to be using either 12ch or 16/2 channel modes.

EdgeTX Trainer Input

To pass the channel information from the backpack back to EdgeTX as trainer port data, set the "HT Start Channel" to "EdgeTX" as in the screenshot below.

HT Start EdgeTX

To make the trainer channel data available to EdgeTX for using in mixes go to "Model Setup" and select "Trainer" and set the Mode as "Master/CRSF".

Trainer Master CRSF

Once this is done you can go to the Mixes tab and set source as a trainer input such as TR1, TR2 etc.

Mixes

With all this configured, channel 1 coming across the backpack should be mapped to channel 10 on the receiver.

NOTE

Again, it is important to remember that if you must also select a packet rate and switch mode that will actually send all the channels you need to the receiver. e.g if you are mapping TR1 to channel, TR2 to channel 11 etc., then you will need to be using either 12ch or 16/2 channel modes.

Example Usage

HDZero Goggle head-tracking

This applies to the HDZero Goggle, HDZero Goggle 2 and HDZero BoxPro+ (not the BoxPro as it does not have the backpack)

  • Make sure that the goggles backpack is updated with the latest version of the HDZero VRX backpack firmware Backpack On
  • In the goggles menu system, go to the "ELRS" section and ensure that the Backpack is "On" Mixes
  • In the "Head Tracker" menu ensure that "Tracking" is set to "On" Mixes

That should be all that is required to get head-tracking with the HDZero goggles.

Boost Pedal

An easy to construct wireless pedal that can send a single channel high/low through the ExpressLRS backpack. This is used for Street League and Underground Drone League RPM BOOST race features, or a Velocidrone Combat weapons trigger.

For more details, see backpack PR https://github.com/ExpressLRS/Backpack/pull/201.