Navigation Team

Indy Robotics Racing

Mission• Inputs from sensors

– GPS, heading, distance, speed, time• Compute position using multiple methods

– DR (primary)– GPS (secondary – primary for correction)– Visual (secondary – secondary for correction)

• Determine when DR position correction is appropriate • Output

– Current position– Vector to next waypoint– CDI (course deviation indication)– Distance traveled, distance remaining– Time elapsed, time remaining– ETE (est time enroute), ETA at projected speed– Avg speed, +/- from planned speed, avg speed to complete, +/- from

planned

Definitions

• CDI=Course Deviation Indication=lateral distance off centerline course

• ETA=Estimated Time of Arrival at the finish line• ETE=Estimated Time Enroute to the finish=sum

of remaining leg times• ATE=Actual Time Enroute for the course

traversed to date• Expected time=sum of reference leg times

traversed to date

What questions does the navigator answer?

• Where are we?– Lat/long/error estimate– CDI (course deviation indicator = lateral distance offset from current vector)

• Where do we go next?– Direct course from current position to next waypoint– Next vector: Heading, distance, reference speed from nxt wpt to nxt wpt+1– Second vector: Heading, distance, reference speed from nxt wpt+1 to nxt wpt+2

• How are we doing?– Elapsed time, elapsed time expected, delta– Average speed, expected average speed, delta– Distance traveled, distance to go– Time remaining to deadline, estimated travel time remaining, delta– ETA, delta to deadline– Average speed required, projected avg speed, delta

Position definition

• Primary method: Dead Reckoning (internal reference calculations) – Computes position 4 times per second– Heading-speed or heading-distance as input

• Error correction: Progressive error of DR is corrected from GPS, inertial navigation, other– No time delay if external reference systems are lost or

delayed

Data Flow

Dead Reckoning Calculator

Current Position/error

CDINext Wpt VectorSecond Wpt vectorETE/ETAAvg/Required speed

Wpt DB

Past Position DB

Heading, distance, speed, time

GPS Position

Position and error comparator

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Error Correction Process

• Error calculator reports that at time t-x the position determined was in error.

• In the past position database, the position at time t-x is corrected

• All subsequent DR vectors and end positions are recalculated and updated in the past position database

• DR calculator re-computes the output series

• Sensors:– GPS (Lat/Long/error): Navcom– Heading (magnetic course): Garmin – AHRS– Speed: TBD– Time: Internal clock– Distance: Odometer or other

Polling and Compute cycles

• GPS: 1 second (or device standard)• Heading: 1 second intervals• Speed: 1 second intervals• Time: na• Distance: 1 second• DR Position computation: 4 Hz • Error comparator: 1 minute

External Reference

• GPS• Visual ID of waypoint• Visual ID of surface features• Visual or other ID of structures like towers.

– Cellphone– Power grid

GPS

• Best accuracy in motion: assume 1 foot• Update cycle: 1 second• Messaging method:

Internal Position Reference

Heading Reference

• Garmin AHRS (primary)– Inertial reference for both heading and attitude (pitch

and roll)

• Aircraft gyrocompass (secondary)– Slaved w/ magnetic correction for precession

• Open Issues– Initial reference setting prior to the race

Odometer

• Trailing or wheel based

• Other

Speed

• GPS speed input

• Direct speed input from the vehicle

Data Management

• Waypoint database and Past Position database• Telemetry database during testing• Ancelus v1.3/Linux • Totally memory resident• Fast

– Lookups @ 5 mil TPS, insert/delete @ 360,000 tps.• Minimum footprint

– About 20kb + dataspace– Dataspace compression of about 5:1 vs typical

relational.• The price is right