Land Mode

LAND Mode attempts to bring the copter straight down and has these features:

  • descends at LAND_SPD_HIGH_MS, if non-zero, (or WP_SPD_DN if zero) using the regular Altitude Hold controller.

  • the pilot can reposition the vehicle using the pitch and roll sticks unless the LAND_REPOSITION parameter is changed to “0”. The throttle stick has no effect by default, although high throttle can cancel landing if enabled via PILOT_THR_BHV.

  • if a rangefinder is being used, or TERRAIN_ENABLE =1 and terrain data is available, the descent speed will then switch to LAND_SPD_MS at LAND_ALT_LOW_M altitude (default is 10m) above ground until landing occurs. If neither terrain data or rangefinder data is available, then altitude above HOME will be used for the speed switch point (if reached).

    ../_images/Land_DescentSpeed1.png

  • below 10m the copter should descend at the rate specified in the LAND_SPD_MS parameter which defaults to 50cm/s.

    ../_images/Land_DescentSpeed2.png

  • Upon reaching the ground the copter will automatically shut-down the motors and disarm the copter if the pilot’s throttle is at minimum.

Note

Copter will recognise that it has landed when ALL of the following are true for approximately one second:

  • Motors are commanded to their lower limit by the vertical position controller

  • Throttle is at minimum

  • No large angle is being requested (roll/pitch target < 15°)

  • No large angle error exists (attitude error < 30°)

  • The airframe is not accelerating downward > 1m/s/s ( >2 m/s/s if Weight on Wheels feature is enabled)

  • Vertical speed is within 1 m/s of zero ( within 2 m/s if Weight on Wheels feature is enabled)

  • If a healthy rangefinder is available, and rangefinder altitude is below 2m

  • Weight-on-Wheels (WoW) sensor (if present) confirms contact or is unknown

Altitude above home is not used as a motor shutoff condition (except when a rangefinder is used,see above). The LAND_ALT_LOW_M parameter (default 10m) only controls the descent speed transition from LAND_SPD_HIGH_MS to LAND_SPD_MS — it has no role in landing detection or disarming.

Note

For Traditional Heli, the low motor check in the above landing detection algorithm is replaced with a check that Collective output is below mid-position (controlled by the vertical position controller, ie in descent). The rotor still may be at governor speed up until Motor Interlock is removed and disarming occurs.

Note

Using a Weight on Wheels (WoW) switch will increase the descent rate and accelerometer ranges that are acceptable for landing detection. This feature is enabled anytime the LGR_WOW_PIN is not disabled.

  • If the copter appears to bounce or balloon back up a couple of times before settling down and turning the props off, try lowering the LAND_SPD_MS parameter a bit.

  • If the vehicle has GPS lock the landing controller will attempt to control its horizontal position, but the pilot can adjust the target horizontal position just as in Loiter mode, unless the LAND_REPOSITION parameter is set to 0.

  • If the vehicle does not have GPS lock the horizontal control will be as in stabilize mode, so the pilot can control the roll and pitch lean angle of the copter, unless the LAND_REPOSITION parameter is set to 0.

Warning

In any Alt Hold based mode including: Alt Hold, Loiter, Auto, Auto NAV_Land or RTL if your copters operation becomes erratic when you are close to the ground or landing (and also if any auto landing procedure results in bouncing or failure to turn off motors properly after landing) you probably have the autopilot situated such that its barometer (altimeter) is being affected by the pressure created by the copters prop-wash against the ground.

  • This is easily verified by looking at the Altimeter reading in your logs and seeing if it spikes or oscillates when near the ground.

  • If this is a problem, move the autopilot out of prop wash effect or shield it with an appropriately ventilated enclosure.

  • Success can be verified by flight test and by log results.