Hello everyone! 

I got my hands on a brand new SpeedyBee F405 V3 + BLS 50A Stack and I've run into my first obstacle! 

I haven't upgraded my Radio system yet and I'm still using my FlySKY CT6B Tx and R6B Rx. Since the F405 flight controller doesn't take in PWM RC Input, I bought an 8 channel PPM encoder. 
Link: https://robu.in/product/pixhawk-ppm-enco...lQQAvD_BwE

I connected the R6B's channels 1-4 to the PWM inputs 1-4 of the PPM encoder and the PPM output to R2 on my flight controller. 
I enabled Serial RX on UART 2 on the betaflight configurator.
Under the RECEIVERS tab, I selected the receiver type as PPM/CPPM and selected the default channel mapping (AETR1234) 

Here's what I'm observing: 

Case1) All 4 channels connected between the PPM encoder and Receiver:
Only the right gimbal movements (Roll and Pitch) are recognized by betaflight
Left gimbal movements (Throttle and Yaw) don't work and are always at their lowest position (around 1050)
3D model of the quad keeps spinning left because of this   

Case2) Only channels 1,2 and 4 are connected between the PPM encoder and Receiver: 
All the three stick movements (Roll, Pitch and Yaw) are recognized by betaflight 

Case3) Only channel 3 is connected between the PPM encoder and Receiver:
Throttle stick movement is recognized by betaflight 

I am using DigitalRadio with the Tx connected to my PC to check the RC Output simultaneously and everything seems to be working fine there! All the stick movements and the auxiliary channels (5 and 6) are recognized! 

I have also tested the same on the latest betaflight firmware (4.4.2) and the problem still persists  

I did an extensive search on the internet and couldn't find a single person facing the same issue! Most of the videos/threads talk about absolutely not getting the receiver to work with betaflight. 
This issue has been eating up my head for a good couple of hours now and it's starting to get really frustrating! 
Any help regarding this would be much appreciated as investing so much money in a new stack would end up being useless if I can't even get the radio link setup properly! Maybe I should try using an S BUS receiver and compatible transmitter but I can't afford a new radio system right now! 

Everything else like the baro, accel, gyro, current and voltage sensors are working just fine! I just want to get the receiver up and running so I can get back in the air!

(07-Jul-2023, 12:50 AM)SuryaKK Wrote: I enabled Serial RX on UART 2 on the betaflight configurator...

That's probably the problem right there... unlike sbus and crsf, ppm is not a serial protocol. Disable that serial port and it should work as expected. This used to be a common mistake when ppm was more popular... since many fc manufacturers would label some pin as "ppm/uartX", which can lead to confusion. Note, there may be a jumper you have to change to switch from serial to ppm. Here's a discussion about setting up ppm on another fc, including jumpers etc... it should give a general direction to head with your fc:

https://forum.flitetest.com/index.php?th...ppm.37573/

edit: Trying to wrap my head around how even the first 2 channels work the way you had it setup. I'm guessing serial port activity interferes with latter pulses on the ppm stream... so only the first few channels get resolved, and the rest are cutoff. Maybe if you changed AETR with this bad setup, it would change what channels betaflight can see (roll and pitch are the first 2 in the stream for AETR). I digress, I remember the good ole days when ppm was the new 1-wire magic that made the ratsnest disappear on everyone's rig, lol.

Hi truglodite! 
This might sound weird after going through your reply because I actually got the PPM signal to work with the Serial RX enabled on UART 2! The PPM encoder that was delivered to me was the one probably at fault. I verified this by making a simple PWM to PPM converter using an Arduino pro mini and it's working flawlessly! 
I decoded the PPM signal coming from the PPM encoder using the same arduino and found that it was in fact only reading the first 2 channels if channel number 3 and 5 were connected! It had no problem reading 4 channels if channels 3 and 5 were not plugged in (both on the arduino decoder and Betaflight) 
Before using the Arduino method, I tried using the PPM encoder on my Holybro mini APM 2.7.2, I shorted the SJ4 jumper and connected the PPM output to RC IN 5 as mentioned on the instruction sheet but I couldn't get it working. 

Haha yes, I have to agree with PPM being a "one wire magic", it surely helps with my OCD of having to achieve the best possible cable management! 



Anyways, I've attached the latest picture of my build. Can't wait for the replacement PPM encoder to arrive so that I can get rid of the Arduino and get a cleaner looking setup! 



I'll soon be writing a post about this build and maybe discuss a few issues I'm facing with it. As of now, it flies pretty well with slightly tweaked PID settings and RPM filtering!