Frsky Flight Controllers Comparison: XSRF3O, XSRF4O, XSRF3PO, XSRF4PO

Following our review of the XSRF3O flight controller with integrated Frsky XSR RX, FrSky provided us with the other 3 flight controllers of the same FC line up to check out: the XSRF4O, XSRF3PO and XSRF4PO.

Check out this post to learn more about How to choose flight controller. This review is written by Artur Banach. Check out our review of the XSRF3O.

These flight controllers are available from the following vendors:

A feature comparison table between these Frsky FC’s.

XSRF3O XSRF3PO XSRF4O XSRF4PO
Processor F3 F3 F4 F4
IMU (Gyro) MPU6050-I2C MPU6050-I2C MPU6000-SPI MPU6000-SPI
PDB Integrated? No Yes No Yes
MicroSD for Blackbox? Yes Yes Yes Yes
Number of PWM outputs 8 8 6 6
Operating Voltage 4V-10V up to 6S 4V-10V up to 6S
Betaflight OSD Yes Yes Yes Yes
Dimension 36mm x 36mm 60mm x 36mm 36mm x 36mm 60mm x 36mm
Weight 6g 14g 6g 14g
Price $40 $50 $50 $60


XSRF3PO

The XSRF3PO flight controller is basically the XSRF3O but with PDB integrated.

Inside the XSRF3PO box:

  • XSRF3O Flight Controller
  • Set of pins for soldering
  • Instruction manual

 

Specs

  • STM32F303 – F3 Processor
  • MPU6050 Gyro
  • Built in Power Distribution Board up to 6S
  • Built in current sensor
  • Built in Betaflight OSD (compatible with Betaflight configurator)
  • Integrated full range XSR radio receiver with Smart Port telemetry
  • Built in Micro SD card slot for BlackBox
  • 60mm x 36m with 30.5mm mounting holes
  • 12.8g in weight

The choice of MPU6050 Gyro is a poor decision in our opinion, because it’s limited to I2C BUS (no SPI) and therefore it can only run a maximum gyro sampling rate of 4KHz.

The board is in rectangular shape due to the amount of components soldered on it. Solder pads for ESC power and signals are in the four corners corresponding to the Betaflight motor order. Solder pads for video section are located at the front, next to the smart port connector (for flashing the built in receiver) and buzzer port.

MicroSD card slot is facing outwards for easy card removal. XSR built in receiver antennas are fitted to the board with W.FL connectors, so they can be easy replaced if needed. Antennas are directed outwards by default. Exposed antenna element is just under 33mm long and both antennas have a total length of 145mm.

Betaflight Settings

The board comes flashed with Betaflight 3.2 (FRSKYF3 Target) and the ports are all pre-configured specifically for SmartPort and receiver and it works out of the box.

XSRF3PO has the same gyro as the XSRF3O and can only do 4K/4K gyro refresh rate and loop time without maxing out CPU load.

Great things about XSRF3PO

  • Integrated RX for cleaner builds and better convenience
  • Good value for money considering it’s basically 3 components in 1 board: FC, PDB and RX
  • MicroSD card logger available for Blackbox
  • Good pads layout
  • Supports up to 8 PWM inputs and supports hex and octo configuration
  • Betaflight is already configured and ready to use

Things to be aware of

  • Bad choice of Gyro
  • Unusual shape might not be possible to use with very tight racing frames
  • With default orientation antennas are sticking side way

XSRF4PO

XSRF4PO is very similar to the XSRF3PO above, with the main difference of F4 processor and MPU6000 SPI gyro.

Specs

  • STMF32F405 – F4 Processor
  • MPU6000 SPI Gyro
  • Built in Power Distribution Board up to 6S
  • Built in current sensor
  • Built in Betaflight OSD (compatible with Betaflight configurator)
  • Integrated full range XSR radio receiver with Smart Port telemetry
  • Built in Micro SD card slot for BlackBox
  • 60mm x 36m with 30.5mm mounting holes
  • 13.6g in weight

XSRF4PO shares the same shape and dimensions as the Frsky F3 PDB board. It can support hexacopter configuration by having 6 PWM outputs. Solder pad arrangement is similar to F3 version.

The board comes flashed with Betaflight 3.2 (with target OMNIBUSF4 for some reason).

Gyro refresh rate and loop time can be set to 8K/8K safely thanks to the MPU6000 gyro and F4 processor.

One common problem with F4 boards is the lack of UART inverters, where you either need built-in inverters or getting the uninverted signal to use SBUS or SmartPort. With the XSRF4PO this isn’t a problem any longer as both SPort and SBUS are working right out of the box.

The rest of the features are identical to the XSRF3PO.

Great things about XSRF4PO

  • Integrated RX for cleaner builds and better convenience
  • Very good value for the price considering it’s basically 3 components in 1 board
  • MicroSD card logger for Blackbox
  • Good pads layout
  • SmartPort and SBUS pre-configured
  • Good gyro choice and plenty of CPU power with the F4 processor

Things to be aware of

  • Unusual shape might not be possible to use with very tight racing frames
  • With default orientation antennas are sticking out sideway

XSRF4O

Last but not least is the XSRF4O board that shares a lot of common features with XSRF3O. It’s basically the XSRF4PO above without the PDB capability.

Inside the box, it comes with:

  • XSRF3O Flight Controller
  • Set of pins for soldering
  • Instruction manual

Specs

  • STM32F405 CPU – F4 Processor
  • MPU6000 SPI Gyro
  • Built in Betaflight OSD
  • Integrated full range XSR radio receiver with Smart Port telemetry
  • Built in Micro SD card slot for BlackBox
  • Operating Voltage Range: 4-10V (it can’t be powered directly from LiPo battery)
  • 36x36mm with 30.5mm mounting holes
  • 7g in weight

The board we have received, unlike other ones, came pre-flashed with Betaflight 3.1.7 (with target OMNIBUSF4) and the receiver and port weren’t setup properly.

Gyro refresh rate and loop time can be set to 8K/8K with the MPU6000 SPI gyro and F4 processor.

Again, despite being an F4 board, you don’t need to worry about UART inverters for SmartPort and SBUS as they work out of the box.

Great things about XSRF4O

  • Integrated RX for cleaner builds and better convenience
  • MicroSD card logger – useful for tuning with Blackbox
  • Good pads layout
  • Supports up to 6 PWM inputs (as opposed to 8 on F3 version)
  • Good gyro choice and plenty of CPU power with F4 processor

Things to be aware of

  • MicroSD card slot orientation on the board is facing inwards making it more difficult to access inside the frame
  • Additional 5V voltage regulator or PDB is required to power this FC

Conclusion

FrSky’s new flight controller line-up is quite interesting because for the first time we have XSR radio receiver incorporated into the main board. It saves hassle of having a separate component to wire up and leaves more space for the build. Each of the boards have different features and prices making it very flexible for different situations.

10 thoughts on “Frsky Flight Controllers Comparison: XSRF3O, XSRF4O, XSRF3PO, XSRF4PO

  1. James

    Is it possible to add GPS to these? If so, what are the options? There doesn’t seem to be any general purpose I/O pins for this.

    Thanks,

    Reply
    1. Oscar Post author

      These FC have limited number of UART’s, and they are really designed for racing and mini quad’s. You should be looking at iNav if you plan to use GPS, they actually have a list of suggested FC you can use.

      Reply
  2. Mark

    It is worth mentioning that the XSRF40 (and possibly the other F4 boards) do not have an exposed UART available. For folks who want to use things like TBS Smartaudio you can’t. No place to solder the wire! I had ordered XSRF40 for a new build and had to send it back. I confirmed the lack of a connection point with FrSky support. Very disappointing.

    Reply
    1. Artur

      I checked with FrSky as well. XSRF4O doesn’t have that but rest of the board do. I was told that XSRF4O will be revised to address this issue.

      Reply
      1. Henri Schomäcker

        Hi, thanks for that hint.
        Do you know of any resources where enabeling TBS SmartAudio via softserial on the led strip is explained?

      2. Henri Schomäcker

        I viewed a lot of videos now, unfortunately without an exact hnit how to achieve it but finally managed it by searching the betaflight docs and reading github.com/betaflight/betaflight/wiki/Single-Wire-Software-Serial

        Now I had an idea how it should work and this is how it’s done:

        Just for the search engines: How to enable Smart Audio with Software Serial (softserial) on the led strip pin on FrSky XSRF4O

        * Solder the SmartAudio cable from the VTX to the LED signal solderpadd on the FC
        * Connect the FC to the BF GUI
        * Dump your BF cli and save it on your harddisk (but you shouldn’t need it)
        * Enable the SOFTSERIAL feature on the Configuration tab
        * Save and reboot into the GUI again
        * Go to the CLI tab
        * Enter the following into the CLI:

        resource
        # …will tell you:
        # …
        # resource LED_STRIP 1 B06
        # …

        # Free pin B06 from LED_STRIP 1:
        resource LED_STRIP 1 NONE

        # Assign pin B06 to the softserial serial_tx 11
        resource serial_tx 11 B06

        # …and save
        save

        * Open the Ports tab in the BF GUI: Now you should see the additional identifier SOFTSERIAL1
        * In the column Peripherals enable TBS SmartAudio with speed on Auto
        * Save and Reboot

        Now check your configuration in your goggles
        You’ll find the VTX config options under: FEATURES -> VTX SA

  3. Stephen Wright

    Hi Oscar…thanks for summing these up. Im not a huge fan of AIO but if you team up the XSRF4PO with the Matek VTX-HV you would get a very lightweight and streamlined build I expect…shame about the antenna sticking out the side! Steve

    Reply

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