Takeoff Mode

The Takeoff flight mode causes the vehicle to take off to a specified height and wait for further input.

  • This mode requires GPS.
  • The vehicle must be armed before this mode can be engaged.
  • This mode is automatic - no user intervention is required to control the vehicle.
  • RC control switches can be used to change flight modes on any vehicle.
  • RC stick movement in a multicopter (or VTOL in multicopter mode) will by default change the vehicle to Position mode unless handling a critical battery failsafe.
  • The Failure Detector will automatically stop the engines if there is a problem on takeoff.

The specific behaviour for each vehicle type is described below.

Multi-copter (MC)

A multi rotor ascends to the altitude defined in MIS_TAKEOFF_ALT and holds position.

RC stick movement will by default change the vehicle to Position mode unless handling a critical battery failsafe.

Takeoff is affected by the following parameters:

Parameter Description
MIS_TAKEOFF_ALT Target altitude during takeoff (default: 2.5m)
MPC_TKO_SPEED Speed of ascent (default: 1.5m/s)
COM_RC_OVERRIDE If enabled, stick movement on a multicopter (or VTOL in multicopter mode) gives control back to the pilot in Position mode (except when vehicle is handling a critical battery failsafe). This can be separately enabled for auto modes and for offboard mode, and is enabled in auto modes by default.

Fixed Wing (FW)

The aircraft takes off in the current direction using either catapult/hand-launch mode or runway takeoff mode. The mode defaults to catapult/hand launch, but can be set to runway takeoff using RWTO_TKOFF. RC stick movement is ignored in both cases.

Catapult/Hand Launch

In catapult/hand launch mode the vehicle waits to detect launch (based on acceleration trigger). On launch it ramps up to full throttle (RWTO_MAX_THR) in about 2 seconds and then performs a full throttle climbout, with minimum 10 degree takeoff pitch. Once it reaches FW_CLMBOUT_DIFF it will transition to Hold mode and loiter.

In addition to the behaviour discussed above there is also a launch detector that may block the launch sequence from starting until some condition is met. For catapult launch this is some acceleration threshold.

Runway Takeoff

The runway takeoff mode has the following phases:

  1. Throttle ramp: Clamped to the runway (pitch fixed, no roll, and heading hold) until reach the minimum airspeed for takeoff (FW_AIRSPD_MIN x RWTO_AIRSPD_SCL).
  2. Takeoff: Increase pitch and continue until vehicle altitude > navigation altitude (RWTO_NAV_ALT).
  3. Climbout: Climb until altitude above ground level > FW_CLMBOUT_DIFF. In this phase roll and heading restrictions are removed.

Fixed Wing Takeoff Parameters

Takeoff is affected by the following parameters:

Parameter Description
RWTO_TKOFF Runway takeoff with landing gear. Default: disabled.
RWTO_MAX_THR Max throttle during runway takeoff.
FW_CLMBOUT_DIFF Climbout Altitude difference. This is used as the target altitude if taking off without a takeoff altitude setpoint (there is no setpoint in takeoff mode, but there is in missions).
FW_AIRSPD_MIN Minimum Airspeed, below which the TECS controller will try to increase airspeed more aggressively.
RWTO_AIRSPD_SCL Min. airspeed scaling factor for takeoff. Pitch is increased when the airspeed reaches: FW_AIRSPD_MIN * RWTO_AIRSPD_SCL
RWTO_NAV_ALT Altitude above ground level (AGL) at which we have enough ground clearance to allow some roll. Until RWTO_NAV_ALT is reached the plane is held level and only rudder is used to keep the heading (see RWTO_HDG). This should be below FW_CLMBOUT_DIFF if FW_CLMBOUT_DIFF > 0.

The vehicle always respects normal FW max/min throttle settings during takeoff (FW_THR_MIN, FW_THR_MAX).

VTOL

VTOLs default to MC mode on boot, and it is generally expected that they will take off in multicopter mode (and also safer).

That said, if transitioned to Fixed wing before takeoff, they will takeoff in Fixed Wing mode.

© PX4 Dev Team. License: CC BY 4.0            Updated: 2020-10-23 00:56:02

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