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This page provides an overview of the basic operation of the ROSflight firmware and the concepts behind the behaviors.

Companion Computer

ROSflight is primarily intended to be used with a companion computer running ROS. The ROS interface is provided by the rosflight_io node. All configuration of the flight controller is done through the ROS service API provided by rosflight_io (see the parameter configuration documentation page). Sensor data such as IMU measurements are streamed from the flight controller to the companion computer and published as ROS topics. Control setpoints can also be sent to the flight controller by publishing to the appropriate ROS topic (see the autonomous flight documentation page).


To avoid confusion, we try to consistently use the following terminology:

  • Flight controller: The embedded board (such as a Revo or Naze32) that runs the ROSflight firmware and performs I/O with sensors and ESCs
  • Companion computer: A Linux computer, running ROS, that is mounted on the vehicle and has a physical, serial connection with the flight controller
  • Offboard control (setpoints): The control setpoints passed from the companion computer to the flight controller. The control is "offboard" from the perspective of the flight controller, even though the computer providing those commands is mounted onboard the vehicle. Perhaps this is not the greatest terminology, but hopefully this helps clear up potential confusion.

The following figure illustrates the interactions between the major components of the system:

System Components

RC Safety Pilot

ROSflight is designed for use with offboard control from experimental and research code. As such, it provides several mechanisms for an RC safety pilot to intervene if something goes wrong with the control setpoints coming from the companion computer:

  • RC override switch: The safety pilot can flip a switch on the transmitter to take back RC control. Attitude and throttle override can be mapped independently, meaning you can choose one or the other, put them on separate switches, or put them both on the same switch. Details on these switches are provided on the RC configuration page.
  • Stick deviations: If a stick is deviated from its center position, then that channel is overridden by RC control. This allows the safety pilot to take control without flipping a switch. This may be useful to provide a momentary correction on a single axis. The fraction of stick travel needed to activate the RC override is controlled by the RC_OVRD_DEV parameter. The OVRD_LAG_TIME parameter controls the amount of time that the override remains active after the sticks return to center.
  • Minimum throttle: By default, the flight controller takes the minimum of the two throttle commands from RC and offboard control setpoints. This allows the safety pilot to drop the throttle quickly if needed. This behavior can be turned on or off with the MIN_THROTTLE parameter.

Arming, Errors & Failsafe

The flight controller can only be armed and disarmed via RC control. Two mechanisms are provided: sticks (left stick down and right to arm, down and left to disarm) and switch. Only one of these options can be active at a time. Details on configuration are given on the RC configuration page.

The firmware runs a number of error checks before allowing the flight controller to arm. Completing the configuration checklist on the Getting Started page should avoid these errors. In addition to a few internal health checks, the following conditions are checked:

  • Mixer: Valid mixer must have been selected (see the Hardware Setup documentation page)
  • IMU calibration: The IMU must have been calibrated since firmware was flashed (it is recommended that you recalibrate often)
  • RC: There must be an active RC connection

In addition to the error checking before arming, the flight controller enters a failsafe mode if the RC connection is lost during flight while armed. While in failsafe mode the flight controller commands level flight with the throttle value defined by the FAILSAFE_THR parameter.

The following is a simplified version of the finite state machine that defines logic used for the arming, error checks, and failsafe operations:

Arming FSM

The state manager also includes functionality for recovering from hard faults if one were to occur, although this is unlikely with unmodified firmware. If a hard fault occurs while the flight controller is armed, the firmware has the ability to immediately rearm after rebooting to enable continued RC control of the vehicle for recovery.


The meaning of the various LEDs is summarized in the following table. The colors of the LEDs may change depending on your specific board:

LED On Off Slow Blink Fast Blink
Power (Blue) Board powered - - -
Info (Green) RC control Offboard control - -
Warning (Red) Armed Disarmed Error (disarmed) Failsafe (armed)