UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB

, An Improved Line-of-Sight Guidance Law for

UAVs

R. Curry, M. Lizarraga, B. Mairs, and G.H. Elkaim

University of California, Santa Cruz

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Accelerating UAV Demand

Military Civilian

Forestry Marine Fisheries Photography Border surveilance

New Missions New Autopilot Designs

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SLUGS Put in your descriptio n

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Line-of-Sight Guidance

Originally proposed by Amidi (1991) for robots

Park, Deyst, How (2007) made significant contributions Theory

Linear Analysis Asymptotic stability

Flight demonstrations A form of pursuit guidance originally

used in air-to-air missiles

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Line-of-Sight Guidance

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Acceleration

Geometry

Kinematics

Combined L1 constant

UAV Bank angle

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Linear Model (Park, Deyst, How)

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Linear Model (cont)

System Response

where

Note: wn increases with Vg

Let

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Linear Model with Roll Dynamics

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Root Locus with Roll Dynamics

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Summary of Guidance

Asymptotically stable assuming instantaneous acceleration response

Reduced stability with increasing ground speed

not specified in operational situations Errors larger than (track acquisition) If desired track does not exist (go direct)

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Guidance

Look ahead distance depends on ground speed

T* is constant Poles independent of ground speed

ALWAYS define an aim point Limit intercept angle (reduce overshoot) Limit down track aim point distance

Large errors and track acquisition

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Guidance2L

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Simulations

6 DOF nonlinear rigid body model of Rascal UAV Hobby aircraft, wing span of 1.2m Inputs: throttle, elevator, aileron, rudder Outputs: 12 state variables

Dryden model wins Constant wind Gust levels depend on height above ground

and mean wind

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and on Waypoints2L1L

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and Circle Tracking2L1L

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Homing Mode

What if there is a destination but no path?

Point ground track from current position to objective Aircraft use “direct to” everyday

uses one guidance law in all conditions

Automatic “Return To Base” if comm failure

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Homing Mode—Return To Base

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Moving “Base”

The homing mode only requires a line of sight to the objective

There is no requirement that the objective be stationary

Useful for tracking moving objectives We used the L2+ homing mode on

moving base without any modification

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RTB with Moving “Base”