Sponsored by: Air Force Research Laboratory

at Eglin Air Force BaseFAMU-FSU College of Engineering

Agenda• Motivation for the project• Scope and needs• Lawnmowing Aspects

– Prototype– Specifications

• Navigation– OOPic– GPS– Wheel Encoders

• Competition Program• Issues Encountered• Conclusions

Project SponsorAir Force Research Laboratory

at Eglin Air Force Base

Contacts: Martin Eilders and Javier Escobar

Autonomous Lawnmower Competition

• Objective– Mow a 150m2 field of grass without

human interaction• Use any available navigation technology

• Must operate safely

• Must be all weather capable

• Judged based on time and accuracy

• Solve the design problems from previous year– GPS not integrated– Excessive motor vibrations– Corroded materials– Hazardous edges

Project Scope

Needs• Integrate GPS technology

• Eliminate vibration problem

• Safe operation

• Compete in the Annual Autonomous Lawnmower Competition

• Use as much existing equipment as possible

• Keep the total cost production under $2000

Final Pro/E Prototype

Actual Prototype

Prototype Specifications• Dimensions = 42” x 31.5” x 14”

• Total Weight = 86 lbs.

• Cutting width = 31”

• Variable cutting height

• Manual and Autonomous Operation

• Speed range = 0 to 6.4 km/hr

Power Specifications• Available power = 13.8 Ahr

• Battery voltage = 25 - 30 volts

• Estimated run time = 25 minutes per charge

• Charging time = 4+ hrs.

• Drive motor specs– 1.6 HP– 13 lbs.

Cutting Mechanism• String trimmers motor assembly

• Trimmer head assembly

Safety Specifications• Kill switches

• Bump switch

OOPic Microcontroller

• All hardware is controlled by same microprocessor• Can multitask hardware objects

– Virtual Circuits are created to link hardware objects together

– Event subroutines can interrupt the regular program when a specified criterion occurs

Global Positioning System• Uses triangulation from satellites to

determine position, speed, and heading of unit

• First used A12 by Thales Navigation

• Switched to DS-GPM since it is built and designed for use with the OOPic

Output from GPS

Wheel Encoder• Track how much each wheel turns

• 10 “Clicks” = 1 Revolution

Competition Program• Main Program

– Uses waypoint guidance– Applies different inputs to drive motors – GPS provides positional information

• Events– If encoder values are not equal

• Will direct mower back to original heading

– If bump switch is depressed• Kills drive motors immediately• Will resume regular program when switch is

released

Issues Encountered

A12 GPS• Output data is not in a consistent format• Speed and time was not accurately captured• A12 Initializes at 600 Baud Rate while OOPic only

allows a choice between 31500, 1200, 2400, or 9600

• Requires special cord– 9-pin to 4-pin– 12 Volts to 5 Volts

• Switch to DS-GPM since it is made for use with OOPic

DS-GPM• Time Constraints

– GPM unexpectedly on backorder

• Data not storing and displaying correctly– Attempted different physical configurations– Attempted different programming options

• Problem pinpointed to I2C connection between GPM and OOPic– Manufacturer recommended returning the GPM

to the distributor for replacement

Lawnmower Path• Drive motor outputs different for same input

– Causing mower to drive in circular path

• Experimentally able to apply different inputs to each motor for same output– Environment affects inputs necessary

– Shorter distances lessen error in path

• Heading output from GPS can be used to correct errors in path

Conclusions• Did we achieve our main goals

• What did we accomplish with the project

• Does the mower go straight