Hey everyone,

This is my first post as I am trying to get into FPV. I have been flying RC planes for years but recently wanted to get into FPV. I have searched everywhere for a solution but couldn't find it so hopefully someone here can help. I bought a Nazgul5 drone which comes with the iFlight SucceX-E F4 2.1 flight controller. I am trying to install my brand new receiver (Spektrum SPM4650) and connecting it per the wiring diagram attached.
TX-2 connects to my signal wire on the receiver. I have the latest version of Betaflight configurator installed and confirm the firmware on the FC is 4.2.0 as expected. 
In betaflight, I have set UART2 to the serial port (tried all others as well) but its not working. I also have the receiver configuration set to SPEKSAT/serial based with SPEKTRUM SRXL2 as the provider.

I have tried using the command line to enter all the manual settings stated on github and such but none of that worked. 
My transmitter is bound to the receiver correctly as i get the telemetry data on the transmitter screen and the light is solid orange indicating a connection. Yet, I get no response on betaflight. its like it cant see the signal from the receiver. I even tried to bypass the UART port and soilder the wires to the board (based on another forum post I read), soildering the signal wire to T6 or R6....but this didnt work either. I finally gave up, and connected my Turnigy i6s (aka frsky) transmitter and S-bus receiver via UART2 port as shown in diagram....changed configurator to S-bus and it WORKS! So I know my port is right, but for some reason the protocol for the Spektrum SRXL2 doesnt seem to work. I would like to use my spektrum transmitter rather than this cheap turnigy remote. 

Does anyone know what else i can try or has anyone had this issue?

The TX-2 pad on the iFlight SucceX-E F4 V2.1 FC is for an inverted SBUS signal from an FrSky receiver. You need to connect the "S" output from the Spektrum SPM4650 receiver to the T2 pad instead which is for an uninverted signal.

(20-Jan-2021, 03:02 PM)SnowLeopardFPV Wrote: The TX-2 pad on the iFlight SucceX-E F4 V2.1 FC is for an inverted SBUS signal from an FrSky receiver. You need to connect the "S" output from the Spektrum SPM4650 receiver to the T2 pad instead which is for an uninverted signal.

Dude you just saved me such a headache! that worked!

NOTE: On the iFlight SucceX-E F4 V2.1 there is no "pad" for T2. its on the UART port. So i just had to pop the wire jumper our and put it in a different slot. 

I made a drawing real quick for whoever may need it in the future.

No problem. Yes, I meant the pin. Saying "pad" is just habit. I should probably say "connection" so it covers either a pad or a pin

(20-Jan-2021, 03:02 PM)SnowLeopardFPV Wrote: The TX-2 pad on the iFlight SucceX-E F4 V2.1 FC is for an inverted SBUS signal from an FrSky receiver. You need to connect the "S" output from the Spektrum SPM4650 receiver to the T2 pad instead which is for an uninverted signal.

Hello. I read your phenomenal answer!
I have a 'spm4650' receiver and 'CrazyF411 flight controller' on Happymodel Crux35 HD FrySky. How shoould I connect them? Could you advice me please?

(21-Jan-2023, 12:28 PM)sdhg0411 Wrote: Hello. I read your phenomenal answer!
I have a 'spm4650' receiver and 'CrazyF411 flight controller' on Happymodel Crux35 HD FrySky. How shoould I connect them? Could you advice me please?

That flight controller has UART 1 inverted for sbus. im not a spektrum guy but based on the above answers the S wire should go to RX1 on that happymodel board.

(21-Jan-2023, 01:00 PM)matt0725 Wrote: That flight controller has UART 1 inverted for sbus. im not a spektrum guy but based on the above answers the S wire should go to RX1 on that happymodel board.

Thank your for your advice but I can not see RX1. Which one is the RX1??

https://www.multirotorguide.com/news/hap...thpick-fc/

You can't use any RX pad (whether inverted or not) for a Spektrum SPM4650 receiver. It has to be connected to a TX pad. UART2 (RX2 and TX2) is being used for the MSP connection for the HD VTX but there is a TX1 pad on the FC so you can connect the "S" pad of the SPM4650 receiver to that and then configure UART1 for "Serial RX" in the Ports tab the configure the other relevant settings in the Receiver tab to be for a Spektrum receiver.

(21-Jan-2023, 02:43 PM)SnowLeopardFPV Wrote: You can't use any RX pad (whether inverted or not) for a Spektrum SPM4650 receiver. It has to be connected to a TX pad. UART2 (RX2 and TX2) is being used for the MSP connection for the HD VTX but there is a TX1 pad on the FC so you can connect the "S" pad of the SPM4650 receiver to that and then configure UART1 for "Serial RX" in the Ports tab the configure the other relevant settings in the Receiver tab to be for a Spektrum receiver.

Thank you for your advise. I can bind with receiver but it dose not work in betaflight(10.9.0-RC5)
I connected TX1 with "s" on the FC and configured UART1 for "Serial RX"in the port tab. Then I choosed "Serial(via UART)" and "SPEKTRUM SRXL2' in receiver tab. But still not working. Could you advise me please?

(22-Jan-2023, 06:55 AM)sdhg0411 Wrote: Thank you for your advise. I can bind with receiver but it dose not work in betaflight(10.9.0-RC5)
I connected TX1 with "s" on the FC and configured UART1 for "Serial RX"in the port tab. Then I choosed "Serial(via UART)" and "SPEKTRUM SRXL2' in receiver tab. But still not working. Could you advise me please?

did your issue resolve? I see the same issue, betaflight (speedybee F405v3) binds with SPM4650 but does not move those colored bars when the radio stick is moved. It stopped after upgraded to the cloud fw  4.2.2. I did select SRXL2 while flashing and wired 
S. -> Tx2.

(19-Jul-2023, 07:11 PM)Jon_B Wrote: did your issue resolve? I see the same issue, betaflight (speedybee F405v3) binds with SPM4650 but does not move those colored bars when the radio stick is moved. It stopped after upgraded to the cloud fw  4.2.2. I did select SRXL2 while flashing and wired 
S. -> Tx2.

Does it work in Betaflight 4.3.2 and/or Betaflight 4.2.11 with the same wiring setup? If you haven't tried that then please do so which will then enable us to narrow down the root cause of the problem being with Betaflight 4.4.x or the wiring connections.

If it works fine under under Betaflight 4.3.2 and/or Betaflight 4.2.11, try re-flashing Betaflight 4.4.x and if it stops working again under that version then please run the "dump", "diff all" and "status" commands in the Betaflight Configurator CLI tab and copy/paste the results back here.

Please also post some good clear photos of the actual wiring and connections between your receiver and flight controller.

(19-Jul-2023, 10:31 PM)SnowLeopardFPV Wrote: Does it work in Betaflight 4.3.2 and/or Betaflight 4.2.11 with the same wiring setup? If you haven't tried that then please do so which will then enable us to narrow down the root cause of the problem being with Betaflight 4.4.x or the wiring connections.

If it works fine under under Betaflight 4.3.2 and/or Betaflight 4.2.11, try re-flashing Betaflight 4.4.x and if it stops working again under that version then please run the "dump", "diff all" and "status" commands in the Betaflight Configurator CLI tab and copy/paste the results back here.

Please also post some good clear photos of the actual wiring and connections between your receiver and flight controller.

It worked with the factory fw from sppedybee (dont know the version), once I upgraded it has been challenging. Anyway Some imrovement with the current vrsion (4.4.2), the stick bars in the receiver tab moves to the correct position for a second and then moves back to  failsafe values. I addition to RX_LOSS, I see THROTTLE signal pops up and goes away in the first tab.

(27-Jul-2023, 03:26 AM)Jon_B Wrote: It worked with the factory fw from sppedybee (dont know the version), once I upgraded it has been challenging. Anyway Some imrovement with the current vrsion (4.4.2), the stick bars in the receiver tab moves to the correct position for a second and then moves back to  failsafe values. I addition to RX_LOSS, I see THROTTLE signal pops up and goes away in the first tab.

You didn't mention in your other thread (HERE) that the stick bars were moving so I just assumed that communication between the Spektrum receiver and the FC just wasn't working at all.

There are some known issues with the endpoints on Spektrum controller. The endpoints need to go from 1000-2000 when you move the stick to it's maximum throw position on either side. If they don't then you need to adjust them because if they go out of range it can result in an RXLOSS condition (where the values go out of a valid min/max range -> rx_min_usec and rx_max_usec values in the CLI) or a THROTTLE condition (where the throttle value is above the configured min value -> min_check value in the CLI).

As far as I'm aware you can't adjust the endpoint values on a Spektrum controller but they can be adjusted in Betaflight by setting the "rxrange" values in the CLI. See Oscar's article at the link below for how to do that...

https://oscarliang.com/adjust-tx-channel-mid-end-point