The principle goal of utilizing a PWM receiver is to drive servos and ESCs straight with PWM alerts with out an FC. However do you know that ExpressLRS PWM receivers also can output serial protocols like SBUS and CRSF, identical to an ordinary serial receiver? On this tutorial, I’ll present you tips on how to allow it. This makes PWM receivers way more versatile throughout completely different fashions, opening up many new prospects.
New to ExpressLRS? Begin right here with our ELRS fundamentals tutorial: https://oscarliang.com/setup-expresslrs-2-4ghz/
What’s Required?
Nothing—simply your ExpressLRS PWM receiver!
Up to now, should you needed digital sign like SBUS or CRSF from a PWM receiver, you’d want an exterior serial converter. However with ExpressLRS, no extra {hardware} is important. These ELRS receivers are so highly effective they’ll generate serial protocols straight.
When to Use SBUS or CRSF
PWM outputs are very best should you’re not utilizing a flight controller (FC)—for instance, in lots of fixed-wing fashions the place servos and ESCs join straight to the receiver (for instance I did that in my Heewing T1: https://oscarliang.com/hee-wing-t1-ranger-no-fc/).
However when utilizing a flight controller, serial protocols like SBUS or CRSF are higher:
- SBUS makes use of only one wire and helps as much as 8 channels.
- CRSF is bi-directional, requiring two wires, helps extra channels in addition to telemetry.
For PWM Receivers With out Devoted Serial Output
Some ExpressLRS receivers—don’t have a devoted serial port. In these circumstances, you may re-purpose PWM channels to behave as serial outputs. These receivers embrace: the Radiomaster ER3Ci, ER4, ER5A, ER5C, ER5Ci, ER5V2, ER6G and ER6GV.
Right here’s how:
Energy on the receiver.
Allow WiFi mode (both by way of the ExpressLRS LUA script in your radio or by ready 60 seconds).
Join your laptop computer/cellphone to the receiver’s WiFi community (ExpressLRS RX) and open the Net UI by getting into 10.0.0.1 in your browser.
Underneath PWM Output, set Channel 2 to “Serial TX”. CH3 will routinely be assigned as Serial RX by default. This implies PWM outputs 2 and three turn out to be your serial port.
Underneath Serial Protocol, choose CRSF or SBUS (common or inverted). You’ll additionally see different choices like MAVLink, HoTT Telemetry, DJI RS Professional, and SUMD, making this characteristic extraordinarily versatile.
Click on Save, and also you’re executed.
Right here I configure my receiver to output SBUS and ensure it’s working utilizing my SBUS tester. In case you’re curious, the instrument I’m utilizing is the ToolKitRC MC8 Battery Checker. It might probably double as a sign generator and reader for PWM, PPM, and SBUS—very helpful for troubleshooting and testing RC-related gear: https://oscarliang.com/toolkitrc-mc8/
Be aware: The remaining PWM channels will nonetheless work as regular. For instance, if CH2 and CH3 are reconfigured for serial output, CH1 will nonetheless output throttle, and CH4 will nonetheless output yaw (assuming your channel map is ready to TAER).
For PWM Receivers with Devoted Serial Output
Some ExpressLRS PWM receivers embrace a devoted serial output port (with RX and TX pins labelled), such because the ER6, ER8, ER8G, and ER8GV.
With these receivers, you don’t should repurpose PWM channels for serial output. Nevertheless, if you’d like, you may nonetheless configure two PWM outputs to behave as a serial port—the flexibleness is there.
Energy on the receiver.
Allow WiFi mode (by way of the ExpressLRS LUA script in your radio or by ready 60 seconds).
Hook up with the receiver’s WiFi community (ExpressLRS RX) and open the Net UI at 10.0.0.1.
Underneath Serial Protocol, choose CRSF or SBUS (common or inverted).
Click on Save. That’s it!
For Non-PWM Receivers (Serial Receivers) to Output SBUS
By default, all ExpressLRS serial receivers output CRSF. If you would like SBUS output as a substitute, comply with this full tutorial: https://oscarliang.com/how-to-output-sbus-from-an-expresslrs-receiver/
The good factor is you may configure whether or not the receiver outputs inverted or uninverted SBUS:
On F4 flight controllers:
- In case your board has a devoted SBUS pad, it’s more likely to have an built-in exterior inverter, on this case, choose inverted SBUS.
- If it doesn’t have a SBUS pad, and you’re solely utilizing an ordinary UART (RX pad), choose uninverted SBUS.
On F7 flight controllers, it doesn’t matter—they assist each natively.
Conclusion
Enabling SBUS or CRSF on ExpressLRS PWM receivers makes them way more versatile, letting you adapt to completely different setups without having to purchase a separate serial receiver. Due to the highly effective and versatile ExpressLRS {hardware}, the method is easy and simple, but unlocks enormous potential.
