Skip to main content

Channels

The channels subprotocols allows the UAV to transmit the input (received from RC) and output (sent to motors/control-surfaces) channel values to the GCS.

Input Channels​

The input channels subprotocol allows the UAV to send the values of its input channels (received from the RC) to the GCS at at fixed intervals.

Messages​

  1. INPUT_CHANNELS_RAW

Sequence​

sequenceDiagram
    participant GCS
    participant UAV

    UAV->>GCS: INPUT_CHANNELS_RAW
    GCS->>GCS: Start/reset timeout
  1. The UAV transmits the raw values of the RC channels at a fixed rate through INPUT_CHANNELS_RAW messages, each containing a complete frame (all channel values)
  2. After receiving an INPUT_CHANNELS_RAW message (while a connection exists), the GCS starts a timeout of a fixed duration. If a timeout was already started, it is reset.
  3. If the timeout expires before the UAV can send the next set of values, the current values are considered stale.

Notes​

  • The INPUT_CHANNELS_RAW message does not require an acknowledgment from the GCS because it is a periodic message sent at a considerable frequency. Acknowledgments can overload the buffer and in case of the GCS not receiving the values, the UAV can still be flown and landed without catastrophic failure (the GCS will report that the values are stale so that the Operator/Pilot are aware of the issue).

Output Channels​

The output channels subprotocol allows the UAV to send the values of its output channels (sent to the motors) to the GCS at at fixed intervals.

Messages​

  1. OUTPUT_CHANNELS_RAW

Sequence​

sequenceDiagram
    participant GCS
    participant UAV

    UAV->>GCS: OUTPUT_CHANNELS_RAW
    GCS->>GCS: Start/reset timeout
  1. The UAV transmits the raw values of the Motor channels at a fixed rate through OUTPUT_CHANNELS_RAW mesages, each containing a complete frame (all channel values).
  2. After receiving an OUTPUT_CHANNELS_RAW message (while a connection exists), the GCS starts a timeout of a fixed duration. If a timeout was already started, it is reset.
  3. If the timeout expires before the UAV can send the next set of values, the current values are considered stale.

Notes​

  • The OUTPUT_CHANNELS_RAW message does not require an acknowledgment from the GCS because it is a periodic message sent at a considerable frequency. Acknowledgments can overload the buffer and in case of the GCS not receiving the values, the UAV can still be flown and landed without catastrophic failure (the GCS will report that the values are stale so that the Operator/Pilot are aware of the issue).