17-04-2012, 05:14 PM
Design and Implementation of a Robotic Lawnmower
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INTRODUCTION
The objective of this paper is to describe the design of the Wright State University Autonomous
Lawnmower, built by undergraduate students. The team is comprised of members from the
Mechanical and Materials Engineering Department, the Computer Science and Engineering
Department, and the Electrical Engineering Department. Each department has their own
individual team and tasks. The mechanical engineers focused on the frame and material to
mount the electronics, the batteries, the electric motors, the touch sensor and the fiberglass shell.
The computer engineers focused on the computer programming and worked with the electrical
engineers to integrate all of the electronics into the computer. The electrical engineers focused
on providing power for all of the electrical systems and helped the computer engineers to
integrate the hardware with the software.
LAWNMOWER DESIGN
The lawnmower frame is composed of 80/20 T-slotted aluminum framing [4], which was chosen
for ease of fabrication. The outside of the frame is covered with 1/32 inch aluminum plating and
a custom fiberglass shield to protect internal components from the weather. Outside the robot, a
custom electric mower deck made from 1/4 inch MIC6 aluminum is suspended from the main
body. The mower deck is comprised of a three blade system, that has a cutting width of 22.5
inches, and a weed eater for trimming.
Frame
In order to minimize cost and weight of the frame, the decision was made to design the frame
using T-slotted extruded aluminum purchased from 80-20. While a steel frame may have been
stronger, the extruded aluminum is strong enough to handle the needs of the lawnmower. The
extruded aluminum also does not require any welding, the pieces are held together with
connectors that are designed for the 80-20 material.
Mower Deck
After considerable research concerning the possibility of purchasing a pre-manufactured deck
and blade system, it was determined that the best choice would be to purchase just the blades and
motors from the Robomower distributor and fabricate a custom deck so that a string trimmer
could be added to one side [5]. A custom deck was designed in SolidWorks with a ¼”
overlap between the blades. A string trimmer was added to the end of the deck so that the mower
can get close to the obstacles without damaging them.
Motors and Rear Wheels
The drive motors are an integral part of the lawnmower. Along with pushing the lawnmower,
they are also responsible for turning. A motor with a 90-degree gearbox was desired to save
space and to allow for mounting the motors external to the main frame.
CONTROL SYSTEMS AND SENSORS
The control system obtains input from the GPS, IMU, ultrasonic sensors, touch sensor, and laser
range finder. This input is processed by the navigation algorithm on the laptop computer. The
computer then sends commands to the controller to change the individual wheel speeds.
CONCLUSION
Mowing a field of grass is a tedious task that the average person prefers to avoid. There are two
options to eliminate this task from a person’s schedule. One is to pay someone else to perform it;
the other is robotics. There is a simple robotic lawnmower on the market, but it is unable to
perform well in fields that are of complex shape or substantial size. The robotic mower proposed
in this paper is a more sophisticated approach using GPS navigation and is capable of mowing
fields of large size and complexity. It is equipped with a motor controller that drives two motors
based on commands sent by the computer.