Date of Award

Fall 11-21-2025

Document Type

Dissertation

Degree Name

Ph.D. in Mechanical Engineering

Organizational Unit

Daniel Felix Ritchie School of Engineering and Computer Science, Mechanical and Materials Engineering

First Advisor

Siavash Rezazadeh

Second Advisor

Mohammad Mahoor

Third Advisor

Peter Laz

Fourth Advisor

Paul Rullkoetter

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Keywords

Electromechanical systems, Embedded systems, Legged-robots, Optimization, Real-time control, System dynamics

Abstract

This dissertation presents a framework for simultaneous optimization of motors, transmissions, and mechanisms across the joints of robotic legs, with the goal of achieving energy efficient, precisely controllable, and stable locomotion in dynamic environments. Within this framework, two novel performance metrics are introduced for separate evaluation of stability during stance and swing. The metrics are first tested in simulation with a reduced order model, which motivates an extended forced-oscillation based reduced-order model that includes an ankle joint and a finite sized foot. The model aligns more closely with human-like gait characteristics, and its human-inspired ankle push off strategy maintains stability against small perturbations, as observed in humans.

A case study demonstrates the importance of considering the two stability metrics together with an energy metric. The study is extended to a multi objective constrained optimization for a 3-D leg mechanism, yielding an anthropomorphic articulated leg with 6 actuated degrees of freedom and an optimal actuator design. Using this leg design, which has mass and inertia distributions similar to those of humans, a humanoid robot, Mithra, was designed and realized. Mithra is 1.75 m tall, has a total mass of 75 kg, and provides leg motion in the three principal planes. Its development included engineering analysis of structural components, sensor system development, real time communication, embedded programming for real time control and motor control, and battery management system development.

Preliminary experiments indicate that Mithra achieves human-like kinematic and dynamic characteristics and provides sufficient actuator and structural strength for tasks such as stair ascent and descent, squatting, and running. Results also show performance that closely matches the elegance of human locomotion and outperform other state-of-the-art humanoid robots. The actuators of Mithra appear capable of supporting human inspired control paradigms and may enable the first electrically actuated humanoid to achieve human-like running at 3 m/s.

Copyright Date

11-2025

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Chathura Lakshan Semasinghe

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

184 pgs

File Size

8.4 MB

Supplementary File Description

Support for Figure 3.4(a) - Stable walking after large external perturbation
File Format: video/mp4
Language: English (eng)
Extent: 0:20 minutes
File Size: 425 KB

Support for Figure 3.4(b) - Unstable (fall) after large external perturbation
File Format: video/mp4
Language: English (eng)
Extent: 0:20 minutes
File Size: 250 KB

Support for Figure 3.7(a) - Stable walking after small external perturbation
File Format: video/mp4
Language: English (eng)
Extent: 0:10 minutes
File Size: 277 KB

Support for Figure 3.7(b) - Unstable (fall) after small external perturbation
File Format: video/mp4
Language: English (eng)
Extent: 0:10 minutes
File Size: 212 KB

Support for Figure 5.7(a) - Free swing of hip flexion (no power)
File Format: video/mp4
Language: English (eng)
Extent: 0:02 minutes
File Size: 78 MB

Support for Figure 5.7(b) - Free swing of knee flexion (no power)
File Format: video/mp4
Language: English (eng)
Extent: 0:01 minutes
File Size: 62.6 MB

Support for Figure 5.9(a) -  Ankle backdrivability test on passive response
File Format: video/mp4
Language: English (eng)
Extent: 0:02 minutes
File Size: 42.1 MB

Support for Figure 5.9(b) -  Ankle backdrivability test on active control
File Format: video/mp4
Language: English (eng)
Extent: 0:01 minutes
File Size: 46.5 MB

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Available for download on Thursday, December 09, 2027



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