Brief Summary
This video provides a comprehensive overview of radio control protocols used in the hobby, focusing on how receivers communicate with other components in a model, such as servos, speed controllers, and flight controllers. It explains various protocols, including PWM, PPM, SBus, and CRSF, highlighting their advantages, disadvantages, and suitability for different applications. The video also touches on Telemetry and recommends CRSF and SBus as the go-to protocols for new builds.
- PWM is the most basic protocol, widely used in cars, boats, and planes without flight controllers, but requires individual wiring for each component.
- PPM improves upon PWM by sending signals one after another down a single wire, but is still an analogue signal and not particularly fast.
- SBus is a digital protocol that sends channel values in a packet, offering faster speeds, no need for calibration, and the ability to send extra information like error checking and fail-safe status.
- CRSF is a modern, fast, and robust protocol that supports both radio control and Telemetry, making it a preferred choice for newer systems like ExpressLRS.
Introduction
The video introduces a discussion on radio control protocols, specifically focusing on how the receiver communicates with other components inside a model, such as servos, speed controllers, and flight controllers. The presenter aims to consolidate information on these protocols, addressing common questions from pilots, especially those new to flight controllers like INAV, Betaflight, and RUDPilot. The video serves as a companion to a previous one on ESC protocols, acknowledging the rapid innovation in this area over the past 8-10 years.
Caveats and Overview of Protocols
The presenter notes that radio control protocols are constantly evolving, with current standards potentially changing in the near future. The focus is primarily on digital protocols like SBus, CRSF, and MAVLink, which are designed for use with flight controllers and stabilisers. A key advantage of modern protocols is their two-way communication, allowing Telemetry data to be sent back to the radio, providing pilots with crucial information like speed, altitude, and battery status.
PWM (Pulse Width Modulation)
PWM is described as the foundational protocol, commonly used in the hobby. It involves three wires per output: ground, +5V, and a signal pin. The length of the pulse sent along the signal wire determines the signal size. A significant drawback is the need for precise measurement of these pulses by the receiver, servo, or speed controller, often requiring calibration. PWM is relatively slow, with standard speeds of 50Hz for analogue servos and up to 150Hz for digital servos, and it only supports one-way communication. Each component requires its own set of three pins, leading to a large number of connections for multiple servos and speed controllers. Despite its limitations, PWM remains widely used in cars, boats, and planes without flight controllers.
PPM (Pulse Position Modulation)
PPM is presented as an improvement over PWM, especially for systems with flight controllers. It sends signals one after the other down a single signal wire. While this reduces the number of wires, PPM is still an analogue signal, requiring accurate pulse measurements. The need to wait for all signals to be sent before the cycle repeats makes it a slower protocol.
SBus
SBus is highlighted as a significant innovation and a widely supported open standard for digital signals. It uses the same three wires as PPM (ground, 5V, and signal), but instead of sending pulses, it sends a digital packet containing all channel values. This allows for much faster communication, as the signal transmission time is consistent regardless of channel values. SBus eliminates the need for calibration, as discrete values are sent for each channel. Additionally, SBus packets can include extra information like error checking and fail-safe status, enhancing reliability and functionality.
Proprietary Protocols
The presenter briefly mentions other protocols like IBus, FPort, DSM, and DSM2, noting that these tend to be proprietary. While they may offer improvements over SBus, their limited support across different manufacturers can lead to compatibility issues. The presenter prefers sticking to open standards for broader compatibility and ease of use.
Telemetry Protocols: SmartPort, MAVLink, and CRSF
The discussion shifts to Telemetry protocols, which enable data transmission from the model back to the radio or PC. SmartPort, developed by FrSky, is a common method where the SBus connection is used for control signals, and Telemetry is sent back via a separate SmartPort pin. MAVLink, used in Pixhawk and U Pilot systems, employs a robust two-cable system (receive and transmit) for both radio control and data transmission, allowing live Telemetry display on a computer. CRSF, popularised by Team Black Sheep and adopted by ExpressLRS, uses four wires (ground, 5V, transmit, and receive) for fast and reliable two-way communication, making it a preferred choice for modern systems.
CRSF in Detail
CRSF is further emphasised as a go-to standard, with the presenter expressing gratitude to Trappy for allowing ExpressLRS to adopt the protocol. Most modern flight controllers have specific ports for CRSF receivers. Connecting the four wires and configuring the flight controller for CRSF provides a robust system.
Recommendations for New Builds
For new builds, the presenter recommends using CRSF with ExpressLRS, TBS Crossfire, or the Tracer system. This setup offers Telemetry, reliable radio control signals, and advanced features. SBus is also recommended as a widely supported open standard, particularly useful for flight stabilisers and older equipment. The presenter suggests using up spare SBus receivers but opting for ExpressLRS with CRSF for new setups.
Conclusion
The video concludes by summarising the benefits of CRSF, which allows both Telemetry and radio control through a single UART, compared to SBus, which requires separate connections for Telemetry. The presenter encourages viewers to ask questions and expresses hope that the information provided clarifies the complexities of radio control protocols.
