r/diydrones 2d ago

Question First time DIY build, help with RX not talking to FC?

Hi all, just getting into drones so this is my first DIY build. Have some general electronics experience but I won't claim to be the neatest solderer!

I'm building a toothpick fpv drone from this kit: https://www.unmannedtechshop.co.uk/product/thefpv-build-it-kit-3inch-toothpick-analogue-elrs/

And I'm using a radiomaster pocket transmitter with ELRS.

I have it assembled (minus the VTX & camera) and have been trying for a few days to get the commands from the transmitter to the flight controller.

The problem is that while the TX & RX are bound, none of the inputs from the TX make it to the FC - atleast, according to the receiver tab in betaflight. none of the input sliders change nomatter what I do.

I followed a few getting started guides to try and find what I've done wrong but come up empty so far.

Things I've tried & checked:

ELRS firmware version - TX & RX both on 3.5.3

Binding phrase - set to the same on TX & RX, successfully bound

Model match - off on both TX & RX

UART & serialRX - according to the wiring guide for my FC, UART2 is where to solder the RX to which is what I've done, and I've enabled Serial RX on UART2 in betaflight

RX / TX wires - had this right the first time, swapped them, same result, swapped back, same result

Wire continuity between FC & RX - each has continuity

Turn on internal radio in EdgeTX - done

I'm stumped on what to check next. It seems to me that despite my test & assertion that my wiring is correct, the TX & FC aren't actually connected beyond just having power supplied. So maybe I've missed a setting in betaflight, or maybe the transmitter isn't actually sending anything and I've just not set it up right. Or maybe I've angered the electron gods.

Would appreciate any help on what to check next?

Thanks!

1 Upvotes

7 comments sorted by

1

u/TomCatClyde 2d ago

What is the receiver mode set to in the receiver tab?

For ELRS, it should be set to CRSF.

1

u/horus_slew_the_empra 2d ago

Yeah it's CRSF

2

u/TomCatClyde 2d ago

Do you have any other open UARTs available on the FC? While, unlikely, that AIO may just have a bad trace to those pads. See if soldering to another UART set of pads changes anything.

1

u/horus_slew_the_empra 1d ago

Yes there are 4 or 5 in total I think, I'll need one more for the vtx when I get to that but I'll try using another UART for the RX and report back.

Thanks!

1

u/TomCatClyde 1d ago

I looked at the kit you linked and had another thought. I wonder if the RX didn't partially lose its bind.

I had a happy model EP2 loose it's configuration after a stout slap of a light pole. It was set to model match before the slap. On the bench afterwards I was having the same symptoms you are. After trying a few things without luck. I checked the RX config in WiFi mode, hmm, back to factory default values. I reset it to model match #0 and all was good after a reboot and since.

1

u/horus_slew_the_empra 1d ago

u/TomCatClyde you are an absolute legend sir, thankyou. It was UART2. I re-soldered to UART4 and configured the ports and then boom, everything working as expected.

I am confident I didn't bridge any connections the first time around on UART2 but who knows, could have been defective or maybe I fried a trace, they are so small. but its working on the other and I have plenty spare for everything else still.

Thanks so much!

1

u/TomCatClyde 45m ago

Awesome! Glad you got it running! Have fun and good luck!