Configuring Telemetry Rates in Ardupilot

This post is an explainer on the telemetry datarates in ArduPilot, plus information and data on how to configure the datarate to fit in lower-bandwidth radio systems.

Typical Datarates

Telemetry radios used in Ardupilot

All datarates in this article are averages and are rounded to 1 decimal place. Does not include actions such as downloading parameters or waypoints. All datarates are in the Vehicle → GCS direction.

ArduPilot telemetry is a series of MAVLink messages output from a UART (or serial) port on the flight controller.

The MAVLink messages may be a streamed message (message is emitted at some regular rate), such as the vehicle’s GPS position or hardware status. Other messages are emitted in response to a command or query from the ground station, such as downloading parameters or a confirmation of a flight mode change.

The following table shows the average datarate of the default streamed messages from the different ArduPilot firmwares at the default rate of 4Hz. Note the datarate whilst the vehicle is armed is slightly higher, as additional streamed messages (such as NAV_CONTROLLER_OUTPUT) are active. The datarate will vary depending on the vehicle hardware and configuration, as additional sensors (such as a 2nd GPS) will increase the datarate.

FirmwareDatarate when disarmedDatarate when armed
Plane3.5 kbytes/sec4 kbytes/sec
Copter3.5 kbytes/sec3.7 kbytes/sec
Rover3.4 kbytes/sec3.9 kbytes/sec

On a typical 57600 baud RF telemetry radio, this equates to 59%-69% of the available radio datarate being used.

Lowering the Datarate

If you are using a lower baud RF link, then ArduPilot’s streaming datarates may need to be trimmed down. There are several methods to do this.

The easiest method is to lower the rate of the streams. By default, a GCS will ask ArduPilot to stream at 4 Hz. This can be changed in Mission Planner in Config→Planner→Telemetry Rates or in MAVProxy via the --streamrate=n commandline option.

So, lowering the streamrates down to 1Hz gives the following average datarates:

FirmwareDatarate when disarmedDatarate when armed
Plane0.9 kbytes/sec1.0 kbytes/sec
Copter0.9 kbytes/sec0.9 kbytes/sec
Rover0.9 kbytes/sec1.0 kbytes/sec

Taking this further, streams can be disabled. For example, you may not want raw sensor readings or RC channel values. In that case, set the “Sensor” and “RC” streams to “0” in Mission Planner. At this time, MAVProxy does not support setting individual streamrates.

If preferred, these streamrates can be set on ArduPilot instead of the GCS 3.

The average datarates are now:

FirmwareDatarate when disarmedDatarate when armed
Plane0.7 kbytes/sec0.8 kbytes/sec
Copter0.6 kbytes/sec0.7 kbytes/sec
Rover0.6 kbytes/sec0.8 kbytes/sec

Individual Message Control

If finer grained control of which MAVLink messages are streamed is desired, the individual messages and rates can be controlled. There are a few methods for doing this.

For this example, a file containing the message ID’s and rate (in milliseconds) is placed in the SD card’s root directory:

message-intervals-chan0.txt

33 200
1 1000
74 2000

The above file tells ArduPilot that chan0 should stream

APSync

To assist users in getting up and running with their Pi-Connect boards, I’ve built a customised build of the APSync software. APSync is a web-based interface for managing an Ardupilot-based flight controller. It also includes low-latency videostreaming and a Wifi hotspot. It has been customised to include the Pi-Connect specific configuration for the Raspberry Pi (although it can be run without the Pi-Connect attached).

It’s easy to install – just go to the software page and download the APSync disk image. Load the image onto an SD card using an image writer and you’ll be good to go. No extra configuration required!