frsky xsrf40 review

FrSky XSRF4O Flight Controller Review and LUA Setup

FrSky XSRF4O Flight Controller Review

I freaking love the FrSky XSRF4O flight controller.  It has so many features crammed on a 36x36mm board.  Because it has an integrated XSR built in the flight controller, you can build your stack super low and clean.

  • F4 processor
  • Built in XSR receiver with SBUS and Full telemetry
  • BetaFlightOSD
  • SD card slot
  • Configurable LED pad
  • Easy to replace antenna wires

See the full specifications on the FrSky XSRF4O product page.

2018 Race Season


I get ask all the time what parts I’d recommend.  The FrSky XSRF4o will be the flight controller I’ll be using in the majority of my race builds.  It will be the flight controller EnvyAstro and SedHendo will be using in their race rigs for 2018 also.  If a component can stand up to the abuse these two dish out then you know it’s freaking tough.  In fact, we’ve been using this flight controller for the past 3 – 5 months and we’ve yet had one fail on us.

There are a lot of F4 flight controllers out there with built in BetaFlightOSD.  There aren’t many that have a built in receiver.  I love that because cause it eliminates one extra component that I have to worry about when building and anytime you can eliminate a component that just reduces the amount of solder points, one less component I have to find a way to mount and one less thing that can fail in a crash.  It makes it able to build super clean also.


frsky xsrf40 reviewI won’t go into too deep on the build of the FrSky XSRF4O cause I’ll be using this flight controller in a PROton race build soon.  I’ll just hit the highlights here.

The first time I used the XSRF4O I didn’t like it.  It needs to be powered by a 5v source and VBAT needs to be connected to the battery so you can monitor your voltage.  I wish they would have just made it be able to be powered directly off the battery.  It’s more of an annoyance than a deal breaker.  If you use an ESC with a 5V BEC and VBAT wire like the Spedix IS30 it’s perfect.  What makes this ESC perfect to use with the XSRF40 is that the wire harness has wires for the 5V and a VBAT.  This makes building super easy and clean.

LUA Script and TBS SmartAudio


I have the most badass readers.  One of my readers Ringo showed me where UART3 is on the board.  To enable the VTX portion of the LUA script, all you have to do is connect the SmartAudio wire from the TBS Unify to TX3.  Then in the ports tab, enable SmartAudio under Peripherals for UART3.  No need to remap the LED.

frsky xsrf40 review


Because this board has so many features built into it, there’s not a lot of room for extra peripherals, or spare UARTS. The XSRF40 doesn’t have any but no worries.  Having the built in XSR it takes up two UARTS, UART1 is SBUS and UART6 is the SmartPort.  It supports LUA script but to get the TBS SmartAudio working you gotta do a simple hack.  You can reconfigure the LED pad to be used for the SmartAudio.

frsky xsrf40 review

Enable Serial and Telemetry on the Configuration tab:

frsky xsrf40 review

In CLI enter these commands:

resource LED_STRIP 1 none

resource SERIAL_TX 11 B06

frsky xsrf40 review

type “save” and enter

In the Ports tab, set UART6 under Telemetry Output “SmartPort” and for SOFTSERIAL under Peripherals select “TBS SmartAudio”

frsky xsrf40 review

frsky xsrf40 reviewIf your Taranis is set up with the LUA scrip, you can get full telemetry, PID tuning and VTX channel/band from the Taranis.  To be able to change the VTX channel/band/power from your Taranis you need to be using the TBS Unify or ImmersionRC Tramp.

The retail price of the XSRF4O is about $50.  I know what you thinking, 50 bucks for a flight controller?  But if you break it down it’s actually not that expensive.  It’s an F4 flight controller with a built in XSR.  Compared to similar setup, a F4 flight controller such as the BetaFlight F4 which is $42 then you add a R-XSR receiver for for $20, that’s $62.  So for less money and a much cleaner install, the FrSky XSRF40 is a hit in my book.  Go try it out and let me know how you like it.

Check back soon as I’ll be using the FrSky XSRF4O in a PROton build post/video.

If you found this post helpful, it would be super cool if you purchased the components from my store or purchase items from my Amazon links.  These posts are expensive and take a loooong time to make so the purchases make it possible for me to keep making them.  Thanks in advance, I greatly appreciate it 🙂






19 responses to “FrSky XSRF4O Flight Controller Review and LUA Setup”

  1. ringo.harrison Avatar

    Hey Mike! I love the frame and the FC so much that I bought two! Hah. I just wanted to let you know I finished wiring mine up and I was able to use UART3. FrSky’s manual doesn’t actually show it, but if you look on the board between the SD card reader and the sport pad you’ll see tiny holes for RX3 and TX3. I am actually using the Matek VTX which allows a Tramp style setup. I connected it to TX3 and configured UART3 in BF for IRC Tramp. I’m able to use the LUA script as well as change the VTX settings in the OSD.

    Figured I’d give you a heads up so you don’t have to jump through the softserial hoop as well as use up your LED pad.

    1. Mike Tseng Avatar
      Mike Tseng

      sweet man! thanks for showing me this. I’m building a quad for UAVfutures right now. I”ll try that on this build.

  2. ZzyzxFPV Avatar

    I’m confused. If the XSRF4O has s.port on UART 6, why does it use channel 8 for RSSI, and not send it with all the other telemetry via the SmartPort?

  3. Rick Avatar

    So you remapped your motors since you flipped the ESC right?

    1. Mike Tseng Avatar
      Mike Tseng

      no, i remapped the LED to be a UART for smart audio but then a customer showed me where UART3 is on the board. no need to remap, see the note on the post.

  4. Luke patterson Avatar
    Luke patterson

    Hi mike what pads are you using to power the flight controller? Also do recommend using a 5v filtered regulator for the vtx? I planned on using the t motor F40 Pro v2 2400kv

    1. Mike Tseng Avatar
      Mike Tseng

      I’m using the spedix is30 which has a v5 out wire coming out of the harness. the power pad for the camera is filtered so there’s no need for an external 5v.

  5. Luke patterson Avatar
    Luke patterson

    Ok, so then does 5v wire coming off the 4in 1
    Get soldered on the the 5v in pad on the flight controller?

    1. Mike Tseng Avatar
      Mike Tseng

      yes sir

  6. Drew Hampton Avatar
    Drew Hampton

    What are the pids for this build? Please

  7. ezequiel lopes Avatar
    ezequiel lopes

    I have two of these boards but one says tx3 and rx3 but the other board says sd and sc on the same pads is this a typo

  8. Dave A Avatar
    Dave A

    I’ve standardised on these boards too – 5 quads so far. Love the simplicity of soldering them up. Thanks for the tip on Smartaudio – I hadn’t notices the TX3 pin before, given the print size and no mention in the doco.

    1. Mike Tseng Avatar
      Mike Tseng

      yeah that tx3 is hard to find. i was remapping the led before i found that!

  9. gerds Avatar

    Anybody tell if “SD” = TX3 / “SC” = RX3 ? …or vice versa? (my XSRF4O has print SC / SD)

    1. Mike Tseng Avatar
      Mike Tseng

      i’m not sure. i’ve never seen that before

  10. Jamie Hall Avatar
    Jamie Hall

    I am brand new to drone building. I have a pdb that sends 5v to my controller, then I wired the ESCs and motors. I still haven’t done vbatt or any camera stuff. Is there a video that I can reference for the camera setup with this FC so that I get the betaflight odd?

    1. Jamie Hall Avatar
      Jamie Hall

      OSD… Not odd

    2. Mike Tseng Avatar
      Mike Tseng

      you can connect the camera and vtx like how it’s wired in this post and you’ll have betaflight osd. just enable it on the configurations screen

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