Configuring INAV on a fixed wing

[Palkina]

This topic is related to our experiences configuring and testing INAV 1.7.2 on a fixed wing. We expect to make it informative and useful for other members of the community.

Quick Background

INAV https://github.com/iNavFlight/inav/wiki is a fork of CleanFlight with a heavy focus upon GPS features for both airplanes and multirotor models.

iNav is being actively developed and currently supports RTH (Return To Home) with a predefined climb height, position hold, waypoints, "follow-me" and many more features.

Objective

To effectively re-use existing resources and electronics on an easy to fly plane.

• Naze32 (10DOF) a control board with iNAV 1.7.2 version
• GPS based on Ublox Neo M6N.
• Radio receiver based on Lemon Rx DSMX Compatible PPM 8-Channel diversity antenna receiver
• Orange DSMX DSM2 Compatible 2.4Ghz Transmitter Module V1.2 on FrSky Taranis X9D Plus Radio.
• The Apprentice

Challenges

Radio
The radio has proven to be a point of failure.

• The use of Spektrum receivers was discarded due to incompatibilities with other Lemon receivers.
• All Spektrum receivers as well as the Lemon ones present a different pulse width ranges when compared to the ones used by FrySky modules. Approximately 1.0 to 2.0ms, compared to 1.1 to 1.9ms for Spektrum or similar. The initial test was made using the Spektrum receiver and the outcome was a run away
• An improper configuration of the Taranis Radio may enable both Radio Transmitters, the original FrySky and the Orange DSMX DSM2 module

Flight Controller

• Firmware upgrade
• Sensor Calibration
• Setting up endpoints for used channels
• Configuration settings for Fixed Wing
• Board alignment. Adjust to the leveled position of the plane in the air
• Especial configuration to support RTH
• Test preparation

Current status

• Pass-through mode tested
• Angle mode tested
• Horizon mode tested
• Navigation Altitude Hold (NAV ALTHOLD) tested.

Pending

• Navigation Altitude Hold and Navigation Position Hold (NAV POSHOLD) combined.
• Test Return To Home (RTH) flight mode
• Configure an adaptive Failsafe
• Test adaptive failsafe
• Add and test FPV
• Configure and test waypoints tasks

Lessons learned

• Follow the KISS principle. Reduce complexity. Avoid mixing different radio links.
• Keep focused on a single pit task and avoid distractions.
• Make small changes and document.
• Avoid rushing.
• When things appear to be too easy, be aware. Take a step back and check and re-asses the potential points of failure.
• Have a companion. Do not discard a second opinion and/or a way of assessing situations, tasks or outcomes.
• Always find the root cause of failures and learn from past mistakes.