Control architecture for the X Tailed Neptune.

[TuptubBuilder]

My reasons for using a frsky R9mm ota 900 mHz receiver paired to a SpeedyBee F405 flight controller using INAV:
My objective is to optimize the receiver antenna location in order to maximize reception.
I am not qualified to go down the “antenna theory” rabbit hole, so suffice it to say: don’t mess with the antenna and mount it vertically with a minimum of surrounding obstructions.
First, the frsky R9mm ota.

1. Long Range: according to Frsky, it has an operating range of 10 km.
2. Compact form factor: 10 x 16 mm
3. 16 channels available via F. Port.

The SpeedyBee F405 Wing APP

1. Low cost, great value
2. 12 pwm outputs
3. Stability control
4. Telemetry

INAV:
Admittedly, using a flight controller is overkill. However, its value is in allowing optimal locations for the receiver antenna and stability hardware (accelerometers and gyros). I also prefer a computer user interface to that of a Transmitter for setup.
Also, having all those channels allows for customization by using INAV programming and transmitter switches. One example is three bow plane operation modes: independent, synchronized and opposed to the x tail. The left slider on the Frsky Tx operates the bow planes independently. Switch SA low works the bow plane and x tail in tandem. This would raise or lower the boat with minimum pitching. Switch SA high operates the bow planes opposed to the x tail. This would provide maximum pitch control.

[TuptubBuilder]

More details on “how to”…

• Update Frsky Tx and Rx to Ethos 1.6.3
• Install INAV 8.0 on WINDOWS OS.
• Install SpeedyBee Driver on WINDOWS OS using ZADIG.
• R9MM: solder wire leads to V_in, GND & Inverted S.Port.
• SpeedyBee: Rx power and ground go to respective SBUS pins. The Rx ‘Inverted S.Port” connects to a Tx pad on any free UART. I used “Tx5” on UART5.
• Follow the SpeedyBee manual to connect ESC and servos. Make sure to NOT connect the ESC power wire.
• INAV values to follow (probably a word doc)
• Useful references: GitHub, You Tube channels: Painless360, Joshua Bardwell, FPV University, FrSky Rc and Mr.D – Falling with style.

[RCENGR]

Interesting. That FC certainly has a lot of capability, I'm curious how easy it will be to set up. Are you going to use it to stabilize pitch or an other axis?

I'm looking at playing with Ardupilot for an autonomous (surface) boat. I think I'll get an F405 Wing Mini though, since I won't need all the power outputs that the full size version has.

[TuptubBuilder]

First, thank you for your response. I’ll try not to ramble on here but I would just like to acknowledge and sing the praises of the Open Source Communities that developed Betaflight, INAV and ardupilot. I also need to thank sub Ed for his pioneering work of using 900 Mhz radios on RC Subs.
Here comes the “but”. Setup was challenging and frustrating and I gave up numerous times.
The first order of business is hardware selection. My first choice was radio gear that ran expressLRS but I had already invested in Frsky equipment and I want just one Tx for all of my boats. The problem with Frsky is the serial communication protocol. It’s based on the original Futaba system. The Frsky S.Bus output needs to be inverted for the SpeedyBee FC. Fortunately, the Frsky R9mm receiver has an inverted S.Bus output. To use it, you must patch into a Tx input on an unused SpeedyBee UART. I chose the SpeedyBee based on reviews and price point. The R9mm and SpeedyBee F405 Wing cost me around 66 USD with tax.
Next is the FC software. INAV is a derivative of Betaflight. Betaflight is really intended for quads whereas INAV includes RC planes, boats and cars. Ardupilot was my first choice but at the time, I was under the impression that it could not be loaded on the SpeedyBee. At this point in time, I’m not sure that’s still true.
I’m using Pitch and Yaw stabilization with “X” tail mixing. That setup is super easy in INAV. The one feature that I don’t like the FC’s arming requirement. I don’t like it and don’t trust it, it has given me a lot of grief. I plan to post the INAV setup values as soon as I get around to documenting it.
Disclaimer: While I have succeeded in getting this setup to work on the bench, I haven’t gone to lake trials. I’ve diverted my efforts in order to build a rescue boat before launching the Neptune due to Bob Martin’s loss of the TEXAS.

[RCENGR]

How easy was it to get the FC telemetry on the transmitter? Which connection did you use?

[TuptubBuilder]

Once you establish the S.Bus connection, telemetry is transmitted back to the Tx. Be aware that battery voltage is not displayed per LiPo cell, just the total.

[TuptubBuilder]

Set up document for INAV

[TuptubBuilder]

Attached is the FrSky setup. It contains the "Mixes" and "RF" pages as well as snap shots of the Telemetry output. "Mixes" just assigns channel and source. "RF" is the usual setup. I was not going to rebind the Rx for the sake of documentation so I hope my memory holds up the next time around. This is all new to me and I haven't explored how to better display the telemetry output. At the present, voltage and current reads are most useful to me. The compass (GPS) and accel values will hopefully serve at some point in the future.