Hi everyone,
 
I am currently building up my first FPV drone using the O3 Air Unit, the Goggles 2 and the SpeedyBee F7 V3 stack. So far, I managed to activate the Air Unit and to make the video transmission from the Air Unit itself to the Goggles 2 work. However, I made an interesting and, to me, also concerning observation: I want to use as a controller the Futaba T6K with an R3001SB T-FHSS receiver. When the flight controller is connected and powered via USB, the status command of the CLI in Betaflight says the RX connection is fine. But when I plug in the battery, which also powers up the air unit (because via USB the air unit is apparently not powered up), it says RXLOSS in the Arming disable flags. At first, I thought it must be something with the flight controller or the receiver, but I could not find anything. But at some point, I plugged out the air unit before I powered up the flight controller with the battery and now, without the air unit actually running, there is also no RXLOSS disarming flag in Betaflight anymore.
 
I did some further testing and it looks like the issue is somewhere in the Betaflight configuration, respectively the flight controller (I am using the SpeedyBee F7 V3). The problem mainly is that as soon as I power up my DJI O3 Air Unit, the flight controller reports “RXLOSS” in the “Arming disable flags”, while everything is fine when the DJI O3 is not running, which is the case when the flight controller is only powered via USB and not via the battery or the air unit not plugged into the flight controller. However, it is not that the connection between radio and receiver is lost, it is more that something is wrong with the connection between receiver and flight controller. I tested it with FASSTest too and observed there the same problem as well. Probably I misconfigured the flight controller. Do you have any ideas what the issue here might be? I basically followed the wiring guide provided on the SpeedyBee website and did the configuration according to tutorials I found on the internet. I tried to export my settings from Betaflight, you can find the file in the attachments.
 
 
Best regards,
Thomas

If you followed their wiring diagram, I think you need to remove the sbus wire from the dji plug.

The sbus wire from the dji plug is running to pad r2. Their wiring diagram also has the receiver running to r2.

The sbus wire on the dji plug is only necessary if you are using the dji controller, at which point you wouldn’t also be wiring in a separate receiver.

I think what’s happening is: when both air unit and your receiver are powered up, you’re sending two different signals to the same pad.

Another option would be to move the sbus wire from your receiver to the rx pad of an unused uart, and change your port settings to match.

However, if you’re using the plugs on the Speedybee, I think simply removing the sbus wire from the dji wiring harness would be the simplest solution.

(20-Mar-2023, 10:25 PM)Lemonyleprosy Wrote: I think what’s happening is: when both air unit and your receiver are powered up, you’re sending two different signals to the same pad.

Yes exactly, SBUS pad is the inverted signal of the respective RX pad, and share the same processor pin, so you cannot run two different devices on it. When powered by USB, the air unit remains dormant so the receiver signal gets through fine. I just had the same thing happen on a vista/ELRS build, it wouldn't arm with lipo plugged in but everything worked on the bench... the ELRS receiver was previously giving me a lot of trouble, so I didn't even want to deal with it, but after several days it suddenly dawned on me I forget to disconnect the air unit sbus wire...

(20-Mar-2023, 10:45 PM)mstc Wrote: …but after several days it suddenly dawned on me I forget to disconnect the air unit sbus wire...

I feel that manufacturers could do a better job of clearly stating that the dji sbus wire needs to be removed when using an external receiver (if their wiring diagram shows both receiver and dji sbus connected to the same uart).

One simple line of text with an asterisk on the wiring diagram could save a lot of folks some needless frustration.

So what you mean is that I should pull out the cable for pin 6, right?

   

(20-Mar-2023, 11:01 PM)Racetom Wrote: So what you mean is that I should pull out the cable for pin 6, right?

Correct.

Ok, I will give it a try, many thanks for your support.

(20-Mar-2023, 10:54 PM)Lemonyleprosy Wrote: I feel that manufacturers could do a better job of clearly stating that the dji sbus wire needs to be removed when using an external receiver (if their wiring diagram shows both receiver and dji sbus connected to the same uart).

One simple line of text with an asterisk on the wiring diagram could save a lot of folks some needless frustration.

They kind of mention it in the iflight manual that I was trying to setup, but hey who reads manuals these days... Pretty soon we can just ask chat-gpt to setup our drones for us and add whatever features we can think of...

Alright, iFlight gets a thumbs up for that.

I’m still all analog, so I don’t pay a whole lot of attention to digital notes.

I pulled out the cable for pin 6 and tested it, now it works as expected, again many thanks for your support.

Awesome!

Happy flying.