Dead Reckoning Lua Script Not Working with Recent ArduPilot

BHAVIK_BHARDWAJ · June 23, 2026, 12:58pm

I am currently working on a Dead Reckoning project using ArduPilot and have been trying to test the available Dead Reckoning Lua script in SITL.

However, the script appears to have been written for an older ArduPilot version and is no longer functioning correctly with recent versions of ArduPilot and Mission Planner. When running SITL, the script either fails to load or encounters compatibility issues due to changes in the Lua API and firmware updates.

Could you please advise on:

Whether there is an updated version of the Dead Reckoning Lua script available.
Any API changes that need to be incorporated to make the script compatible with current ArduPilot release

I would appreciate any guidance, documentation, or example scripts that can help migrate the existing implementation to the latest firmware versions.

Yuri_Rage · June 23, 2026, 3:36pm

Lines 159 and 160 need updating to:

local wp_speed_up = Parameter("WPNAV_SPEED_UP")        -- maximum climb rate in m/s from WPNAV_SPEED_UP
local wp_accel_z = Parameter("WPNAV_ACCEL_Z")          -- maximum vertical acceleration in m/s from WPNAV_ACCEL_Z

Yuri_Rage · June 24, 2026, 6:01am

I made an error in my previous post and associated (now closed) PR. The current script actually has the correct parameter names for the master branch (4.8-dev).

The changes noted above are a reversion to the 4.6 stable branch, and the script for that branch can be downloaded here:

github.com/ArduPilot/ardupilot

libraries/AP_Scripting/applets/copter-deadreckon-home.lua

ArduPilot-4.6

-- Copter attempts to fly home using dead reckoning if the GPS quality deteriorates or an EKF failsafe triggers
--
-- CAUTION: This script only works for Copter 4.3 (and higher)
-- this script checks for low GPS quality and/or an EKF failsafe and if either occurs, flies in the last known direction towards home
--
-- DR_ENABLE : 1 = enabled, 0 = disabled
-- DR_ENABLE_DIST : distance from home (in meters) beyond which the dead reckoning will be enabled
-- DR_GPS_SACC_MAX : GPS speed accuracy maximum, above which deadreckoning home will begin (default is 0.8).  Lower values trigger with good GPS quality, higher values will allow poorer GPS before triggering. Set to 0 to disable use of GPS speed accuracy.
-- DR_GPS_SAT_MIN : GPS satellite count threshold below which deadreckoning home will begin (default is 6).  Higher values trigger with good GPS quality, Lower values trigger with worse GPS quality. Set to 0 to disable use of GPS satellite count.
-- DR_GPS_TRIGG_SEC : GPS checks must fail for this many seconds before dead reckoning will be triggered.
-- DR_FLY_ANGLE : lean angle (in degrees) during deadreckoning.  Most vehicles reach maximum speed at 22deg
-- DR_FLY_ALT_MIN : min alt (above home in meters) during deadreckoning. zero to return at current alt
-- DR_FLY_TIMEOUT : timeout (in seconds).  Vehicle will attempt to switch to NEXT_MODE after this many seconds of deadreckoning.  If it cannot switch modes it will continue in Guided_NoGPS.  Set to 0 to disable timeout
-- DR_NEXT_MODE : flight mode vehicle will change to when GPS / EKF recovers or DR_FLY_TIMEOUT expires.  Default is 6=RTL, see FLTMODE1 parameter description for list of flight mode number.  Set to -1 to return to mode used before deadreckoning was triggered

-- How to use:
--   1. set SCR_ENABLE = 1 to enable scripting (and reboot the autopilot)
--   2. set SCR_HEAP_SIZE to 80000 or higher to allocate enough memory for this script
--   3. set DR_ENABLE = 1 to enable dead reckoning
--   4. optionally set DR_GPS_SACC_MAX and/or DR_GPS_SAT_MIN parameters to adjust how bad the GPS quality must be before triggering

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