I started putting Nexus-XR with INAV into my Freewing jets and wanted to report on my observations.
Flashing INAV works with the INAV Configurator and the only things that need to be changed is to enable the PWM outputs, and add/reorder channels as needed. For example by default the airplane config uses two aileron channels, so with the F-22 90mm V2 I only needed one. This can easily be changed in the "Outputs" tab. The default settings in ELRS work fine, I'd keep it at the 333Hz mode. I recommend against using F500 or F1000, those modes are no better than DSM-X while the normal modes (150, 250, 333, 500Hz) are using CSS (Chirp Spread Spectrum), like LoRa. You won't notice a difference with a fixed wing aircraft.
Physical installation notes:
F-22:
No special considerations needed. I reversed the direction, if you also do this then go into Alignment and add 180 degrees to the Yaw offset
F-16:
The F-16 has a downward slope (regardless of whether you put it onto the platform where the blue box sits, or below that) so you will need to add a few degrees of offset.
I also installed at a 90 degree yaw offset. Extend your gear, place the airplane on a level surface, and adjust the alignment offset until you get 0 degree pitch and 0 degree roll. Note that these offsets are relative to the stock FC orientation, i.e. pitch will always offset the pitch as seen on the axis from the antenna ports to the servo ports, with the servo ports being "forward". If you install at a 90 degree angle like me this can be a bit confusing.
Channel Setup:
You'll need to add a few servo output channels in the INAV controller. You do this via the Mixer, and "Add mixer rule". I set up both the F-22 and the F-16 identically:
On the transmitter, I set up arming via channel 9: Model/Internal RF/Arm using.../Switch, then go to Mixes and set up channel 9 as source=MAX, switch=your arming switch
In INAV, go to Modes and set up arming via channel 9 too.
Channel 5 is used for Airbrakes (F-16) or Flaps (F-22)
Channel 6 is for sending various commands to the FC, in my case switching between manual mode, ACRO mode (note: ACRO is active if no other mode is selected), and AUTOTUNE.
Channel 7 is gear, Channel 8 is ESC Reverse.
Physical connections:
S1 = Aileron
S2 = Elevatpr
S3 = Flaps (F-22) or Brakes (F-16)
TAIL = Rudder
ESC = ESC
RPM = Not connected
TLM = Not connected
AUX = Landing Gear
SBUS = ESC Reverse
Note: I tried having throttle come out on physical connector number 3 (S3) but that didn't seem to work right. So I just had it come out on the ESC port (output 5)
INAV Version: 9.0.1
Gains/PIFF: In the F-22 90mm V2 I started out with the standard gains, which were flyable. The plane was sluggish, but that's preferable to oscillation. Thanks to good physical trim I didn't have to do autotrim, but you should definitely make sure your plane doesn't require any TX trim before continuing. Once you have your transmitter trims set to 0 and the plane flies straight in manual mode without any intervention, do Autotune.
So far I performed three flights with autotune and found that the responsiveness got better and better.
Expo: REMOVE the expo setting from your transmitter, and configure those values inside INAV instead. There's two sets of expo values in INAV, one for stabilized modes, and one for manual (RC) mode. I just set mine to the same values. Default is around 30 which, if you forget to do this step, isn't unflyable but obviously doesn't feel great.
Servo neutral: Everything has to be centered on the transmitter. Set neutral via INAV only. I had to adjust elevator neutral on the F-16.
Max Servo Travel: Make sure you set your max travel for aileron, elevator and rudder inside INAV, not on your transmitter. Also, it's normal if your control surface throw is reduced a bit if you're not in manual mode. I had to adjust max travel on the F-22 since I had set reductions on my transmitter. The F-16 was 100% so no changes were needed.
TLDR: Start with default values, set Ail/Elev/Rud neutral, travel and expo in inav instead of via your transmitter, use Autotrim or physically trim your aircraft so transmitter trim is at zero, use Autotune at half or 2/3rd throttle.
Remember to read the documentation on how to perform autotrim and autotune. It's not difficult but if you disarm before saving your autotune settings, the improvements are lost.
How does it compare to a regular gyro, or why should you consider a Nexus-XR? Well, if you're using ELRS, this is a no-brainer. This is a extremely well built piece of kit with tons of extensibility, there's many free UART ports that you can use for GPS, Pitot tube, etc.
This opens up the possibility of changing the stabilization depending on speed - you have high gains when flying slow, and lower gains when flying fast.
The ELRS receiver is 2.4GHz only, but since you can easily get tens of kilometers of range with CSS, and most ELRS transmitters support dynamic power output of 250mW, 500mW or even 1W, I don't really miss Sub-GHz for a jet like this.
NOTE: I haven't flown the F-16 with this setup yet. Will update after the first few flights.
Flashing INAV works with the INAV Configurator and the only things that need to be changed is to enable the PWM outputs, and add/reorder channels as needed. For example by default the airplane config uses two aileron channels, so with the F-22 90mm V2 I only needed one. This can easily be changed in the "Outputs" tab. The default settings in ELRS work fine, I'd keep it at the 333Hz mode. I recommend against using F500 or F1000, those modes are no better than DSM-X while the normal modes (150, 250, 333, 500Hz) are using CSS (Chirp Spread Spectrum), like LoRa. You won't notice a difference with a fixed wing aircraft.
Physical installation notes:
F-22:
No special considerations needed. I reversed the direction, if you also do this then go into Alignment and add 180 degrees to the Yaw offset
F-16:
The F-16 has a downward slope (regardless of whether you put it onto the platform where the blue box sits, or below that) so you will need to add a few degrees of offset.
I also installed at a 90 degree yaw offset. Extend your gear, place the airplane on a level surface, and adjust the alignment offset until you get 0 degree pitch and 0 degree roll. Note that these offsets are relative to the stock FC orientation, i.e. pitch will always offset the pitch as seen on the axis from the antenna ports to the servo ports, with the servo ports being "forward". If you install at a 90 degree angle like me this can be a bit confusing.
Channel Setup:
You'll need to add a few servo output channels in the INAV controller. You do this via the Mixer, and "Add mixer rule". I set up both the F-22 and the F-16 identically:
On the transmitter, I set up arming via channel 9: Model/Internal RF/Arm using.../Switch, then go to Mixes and set up channel 9 as source=MAX, switch=your arming switch
In INAV, go to Modes and set up arming via channel 9 too.
Channel 5 is used for Airbrakes (F-16) or Flaps (F-22)
Channel 6 is for sending various commands to the FC, in my case switching between manual mode, ACRO mode (note: ACRO is active if no other mode is selected), and AUTOTUNE.
Channel 7 is gear, Channel 8 is ESC Reverse.
Physical connections:
S1 = Aileron
S2 = Elevatpr
S3 = Flaps (F-22) or Brakes (F-16)
TAIL = Rudder
ESC = ESC
RPM = Not connected
TLM = Not connected
AUX = Landing Gear
SBUS = ESC Reverse
Note: I tried having throttle come out on physical connector number 3 (S3) but that didn't seem to work right. So I just had it come out on the ESC port (output 5)
INAV Version: 9.0.1
Gains/PIFF: In the F-22 90mm V2 I started out with the standard gains, which were flyable. The plane was sluggish, but that's preferable to oscillation. Thanks to good physical trim I didn't have to do autotrim, but you should definitely make sure your plane doesn't require any TX trim before continuing. Once you have your transmitter trims set to 0 and the plane flies straight in manual mode without any intervention, do Autotune.
So far I performed three flights with autotune and found that the responsiveness got better and better.
Expo: REMOVE the expo setting from your transmitter, and configure those values inside INAV instead. There's two sets of expo values in INAV, one for stabilized modes, and one for manual (RC) mode. I just set mine to the same values. Default is around 30 which, if you forget to do this step, isn't unflyable but obviously doesn't feel great.
Servo neutral: Everything has to be centered on the transmitter. Set neutral via INAV only. I had to adjust elevator neutral on the F-16.
Max Servo Travel: Make sure you set your max travel for aileron, elevator and rudder inside INAV, not on your transmitter. Also, it's normal if your control surface throw is reduced a bit if you're not in manual mode. I had to adjust max travel on the F-22 since I had set reductions on my transmitter. The F-16 was 100% so no changes were needed.
TLDR: Start with default values, set Ail/Elev/Rud neutral, travel and expo in inav instead of via your transmitter, use Autotrim or physically trim your aircraft so transmitter trim is at zero, use Autotune at half or 2/3rd throttle.
Remember to read the documentation on how to perform autotrim and autotune. It's not difficult but if you disarm before saving your autotune settings, the improvements are lost.
How does it compare to a regular gyro, or why should you consider a Nexus-XR? Well, if you're using ELRS, this is a no-brainer. This is a extremely well built piece of kit with tons of extensibility, there's many free UART ports that you can use for GPS, Pitot tube, etc.
This opens up the possibility of changing the stabilization depending on speed - you have high gains when flying slow, and lower gains when flying fast.
The ELRS receiver is 2.4GHz only, but since you can easily get tens of kilometers of range with CSS, and most ELRS transmitters support dynamic power output of 250mW, 500mW or even 1W, I don't really miss Sub-GHz for a jet like this.
NOTE: I haven't flown the F-16 with this setup yet. Will update after the first few flights.
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