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Overview

The PLDP parameter group configures the Autonomous Payload Placement (Payload Place) feature. This mode allows the drone to descend over a target, detect when the payload has touched the ground (e.g., via slack in the winch or a weight-off-hook sensor), and autonomously release it.

Key Concepts

1. Touchdown Detection (PLDP_THRESH)

The system monitors the motor thrust required to hover. When the payload touches the ground, the drone becomes "lighter," and the required thrust drops.

  • PLDP_THRESH: The percentage drop in thrust required to trigger the "Touchdown" state.

2. Descent Speed (PLDP_SPEED_DN)

Defines the slow, controlled speed used for the final drop-off.

Parameter Breakdown

  • PLDP_THRESH: Thrust change threshold.
  • PLDP_DELAY: Time to wait after touchdown before releasing the gripper.
  • PLDP_RNG_MAX: Maximum altitude allowed to start the placement procedure.

Developer Notes

  • Library: libraries/AC_PayloadPlace.
  • Mission Item: Triggered by the NAV_PAYLOAD_PLACE waypoint.

PLDP_RNG_MAX

m
Default 0
Range 0 100

Payload-Place Max Range (PLDP_RNG_MAX)

Description

PLDP_RNG_MAX is a configuration setting for the Payload Place autonomous mission command.

In "Payload Place" mode, the drone descends until it detects that the package has touched the ground. This detection relies on a rangefinder (Lidar) to see how far away the ground is. This parameter tells the autopilot: "Only start looking for the ground when the rangefinder says we are closer than this height."

  • 0: Disabled.
  • Value (m): The height threshold (e.g. 5.0m) to begin the final placement phase.

Tuning & Behavior

  • Safety: This prevents the drone from misinterpreting rangefinder "noise" at high altitudes as a landing event.
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PLDP_SPEED_DN

cm/s
Default 50
Range 10 500

Payload-Place Descent Speed (PLDP_SPEED_DN)

Description

PLDP_SPEED_DN sets the vertical speed of the drone as it lowers the package to the ground.

View Source

Payload Place climb delay

PLDP_DELAY: Payload Place climb delay

Description

Delay after release, in seconds, before aircraft starts to climb back to starting altitude.

Values

  • Range: 0 to 120
  • Units: s
  • Default: 0.0

Description

This parameter is used during the "Payload Place" mission command.

  • Function: After the drone detects the payload has touched down (via thrust loss or rangefinder check) and the gripper has released, the drone will wait for this many seconds on the ground (or hovering low) before ascending to return to the mission altitude.
  • Usage: Useful to ensure the load is fully detached and the hook is clear before lifting off.
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Payload Place thrust ratio threshold

PLDP_THRESH: Payload Place thrust ratio threshold

Description

Ratio of vertical thrust during descent below which payload touchdown will trigger.

Values

  • Range: 0.5 to 0.9
  • Default: 0.9

Description

This parameter sets the sensitivity for detecting when the payload has touched the ground.

  • Mechanism: As the drone lowers the payload, the weight on the motors decreases. When the throttle output drops to this percentage of the average hover throttle (while descending), the autopilot assumes the load is now supported by the ground.
  • Example: If hover throttle is 50% and PLDP_THRESH is 0.9, detection triggers when throttle drops to 45% (0.9 * 50%).
  • Lower Value: Harder to trigger. Requires more weight off-loading (slacker line) before release.
  • Higher Value: Easier to trigger. Risk of premature release if the drone descends quickly.
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Pitch Axis Configuration (PITCH) Precision Landing Configuration (PLND)