Publication Date

2024

Document Type

Dissertation/Thesis

First Advisor

Coller, Brianno

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Mechanical Engineering

Abstract

The work proposed in this thesis is motivated by observations of one-wheel vehicles called monocycles. Whereas the unicycle has the rider sitting on a seat above the wheel, the monocycle’s rider sits inside a large circular hoop that serves as the wheel. Due to the position of the rider inside the wheel, it lowers the overall center of mass of the vehicle below the center of the wheel. For this reason, the uncontrolled longitudinal (forward/backward, or drive axis) dynamics are stable. For modest speeds above a certain threshold, the lateral (side-to-side, or lean axis) dynamics of the monocycle are also stable. This lateral stability comes from the same gyroscopic effect that causes a rolling disk to become increasingly stable at higher speeds. Monocycles are typically powered by a motor, so it is rather easy for the rider to quickly pass through the stability threshold and experience steady forward motion. Video evidence suggests two observations of monocycles and their dynamics that appear to be particularly interesting.

1. At least two different designs of the monocycle experience a similar wobble instability at relatively high speed. Once these instabilities occur, the wobble oscillation grows and eventually leads to the monocycle crashing. As the speed of a stable wheel increases, it gets farther from the stability boundary [1][2]. This raises two questions. Why does instability occur? And can these dynamics be controlled to avoid such an instability?

2. The rider typically controls the lean axis dynamics of the monocycle by a combination of leaning side-to-side, and by dragging one’s feet on the ground and providing pushes against the ground, causing tilting moments about the drive axis. Such actuation appears to be highly ineffective and impractical. As a result, the monocycle is much less maneuverable than a motorcycle, and it seems unlikely to have sufficient authority to counteract instabilities encountered in observation 1.

From these two observations, the research team has designed a small-scale monocycle-like robot. It is worth noting that this thesis is primarily concerned with the design (mechanically and electrically) of the robotic device. The following stepsafter the construction would be the development of the control algorithms to attempt stabilizing the monocycle and comparing results to full-scale monocycles. In any case, the hope is to explore the dynamics and control of rolling wheel locomotion through monocycles and more generally. The design and construction of the robot is just the first step of the larger project and will continue beyond this thesis.

The main wheel of the robot is 58 cm in diameter. There are three DC brushless motors to run this robot. One provides a torque about the drive axis to propel the wheel forward and backward. The other two are positioned on a hanging carriage that does not rotate with the wheel. These motors are positioned such that their rotational axes are perpendicular to each other inside the wheel to take advantage of the moment vectors these motors can generate. These inertia disks amplify the magnitude of the moment vectors by creating a resistive torque to the motors to be able to manipulate the wheel asdesired from the user using a wireless gamepad. If manipulated correctly, these moment vectors can cause rotations in the lean and steering axes. Finally, this hanging carriage has an on-board computer coupled with an Inertial Measurement Unit (IMU) in order to process orientation of the wheel and compute motions for the three motors in order to maintain stability of the robot.

Extent

83 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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