High-accuracy Dead-reckoning

System (HADRS) for Manned

and Unmanned Ground Vehicles

PI: Johann Borenstein* Research Professor at the University of Michigan

* 28 years experience in GPS-free position estimation for mobile robots and pedestrians

Mobile Robotics Lab

High-accuracy Dead-reckoning System (HADRS)

HADRS works on any wheeled or tracked ground vehicle.

Works on any terrain, including rugged, steeply inclined terrain.

Requires only a power connection and

wheel/track encoder data from the host vehicle, or our proprietary, retrofittable add-on encoders.

Optional components:

retrofittable add-on

encoders

can be mounted to almost any vehicle in less than one hour

no need to access vehicle’s own odometry system

Trajectory-plotting OCU for tele-operator support.

HADRS installed on a Packbot. HADRS fits neatly into 1/3 of the

payload bay of a Packbot, but can be mounted on any vehicle

Features

Works without GPS, computer vision, beacons, or any other external references

but can accommodated and integrate optional external GPS.

Is indifferent to environment: indoors, outdoors, urban, or rural.

Is small-sized (fits into 1/3 Packbot payload bay).

Is designed for minimal power consumption.

Outputs JAUS compatible, time-stamped X, Y, Z, and heading data stream at 10 Hz.

Outputs data via Ethernet, WiFi, RF, or long-range data modem.

Is unaffected by extreme operating temperatures.

Performance For missions of up to 30 minutes duration:

average position error: 0.5% of distance traveled even on rugged terrain;

maximum position error: 1% of distance traveled

Average heading error: 1°

Errors may be larger on deformable terrain (sand, mud) or any other terrain that promotes excessive track slippage.

For longer missions

Position errors increase at ~1% for every 30 minutes of operation.

HADR Description – Main Components Controlled by a Gumstix computer-on-module.

Sensor modalities:

NavChip inertial measurement unit (IMU)

KVH single-axis fiber optic gyro (FOG)

Host’s odometry OR our add-on encoder system.

Active temperature stabilization for FOG and IMU.

Optional:

Integration with external GPS receiver.

Operator console unit

Version 1: Text only

Version 2: trajectory plotter to support tele-operation

GumstixComputer-on-Module

USB Hub

External

GPS (optional)

Ethernet

or WiFi

Optional OCU(For convenience only, not needed at runtime)

Initialization, mode

selection, debugging

Optional WiFi,

USB, or RF modem

HADR System

Add-on

encoders(optional)

KVH FOG

Closed-loop

temperature

stabilization

IMU

Closed-loop

temperature

stabilization

Host

ComputerComputed pose

Streaming at 10 Hz

Main components of the HADRS

Retrofittable Add-on Encoders

Add-on encoder sub-system comprises two encoders.

Each encoder consists of

1. a pair of latching hall-effect sensors mounted to the robot’s chassis next to a track sprocket or wheel,

2. a laser-cut plastic encoder disk sized to fit inside the sprocket

Each encoder disk has between 4 to 18 press-fit neodymium magnets arranged in alternating north-south orientation.

Function:

As the sprocket turns, alternating magnetic poles pass over the hall-effect sensors, generating quadrature signals.

Retrofittable add-on encoder system, here

fitted to a Packbot track drive sprocket

Experimental Results with HADRS – Run 1

Red curve: Trajectory produced by HADRS

Faint orange curve: Trajectory from consumer-grade GPS used for ground truth. (GPS got a “fix” only at Point ‘A’, therefore the GPS trajectory starts only at ‘A’. )

Total travel distance: 976 m

Total travel time: 23.5 min

Return Position Error: 1.5 m (= 0.15% of total distance)

Largest position error anywhere during this run (near x = -190 m, y = -270 m): ~3 m (= 0.3% of total distance)

Steepest slope traversed: ~17° on grass (see photo inset taken near Point A)

Challenges in this run:

partially sloping terrain,

zig-zagging south of ‘A’,

traverse of several curbs.

Trajectory of Run 1 with the

HADR system installed on a Packbot. To visualize the slope of the terrain, the photo inset

shows the experimenter standing near Point ‘A’ -270

-250

-230

-210

-190

-170

-150

-130

-110

-90

-70

-50

-30

-10

10

-230 -210 -190 -170 -150 -130 -110 -90 -70 -50 -30 -10 10

Y [

m]

X [m]

HADRS Position

A

Experimental Results with HADRS – Run 2

Red curve: trajectory recorded by the HADR system

Total travel distance: 676 m

Total travel time: 28.5 min

Return Position Error: 1.04 m (=0.15% of total distance traveled)

Largest position error anywhere during this run: ~2 m (=0.3% of total distance traveled)

Steepest slope traversed: 10°-15° on grass

Challenges in this experiment:

partially sloping terrain,

traverse of several curbs

Trajectory of Run 2 with the HADR

system installed on a PackBot -140

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

-230 -220 -210 -200 -190 -180 -170 -160 -150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10

Y [

m]

X [m]

HADRS Position

Slope down ~10-15o

Acknowledgements and Disclaimers Acknowledgements

Parts of this Project Agreement Holder (PAH) effort was sponsored by the U.S. Government under Other Transaction number W 15QKN-08-9-0001 between the Robotics Technology Consortium, Inc, and the Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon.

Some parts of this effort were supported by the Ground Robotics Reliability Center (GRRC) at the University of Michigan, with funding from government contract DoD-DoA W56H2V-04-2-0001 through the Joint Center for Robotics.

Disclaimer

The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the U.S. Government.