Document Type

Thesis - Open Access

Award Date

2025

Degree Name

Master of Science (MS)

Department / School

Mechanical Engineering

First Advisor

Todd Letcher

Abstract

This thesis presents the design, implementation, and validation of the Mid Scale Rover Gravity Offloader (MRGO), a terrestrial testbed developed to simulate partial-gravity conditions for planetary rover testing within a three-dimensional environment. The MRGO enables consistent, user-defined offloading force as a rover drives freely within a 20 by 18 ft test area, while a stepper motor rail gantry autonomously tracks the rover’s motion and maintains overhead alignment. Mounted to the moving gantry is a vertical carriage column that houses the offloading mechanism, which accommodates up to 5 ft of vertical displacement without loss of force accuracy. This configuration allows realistic evaluation of rover traction, suspension dynamics, and terrain interaction under reduced gravity conditions analogous to those on the Moon or Mars. At the core of the system is a counterweight-based offloading mechanism integrated within the gantry’s vertical column. The mechanism consists of a guided weight stack connected to the rover through a steel cable routed over pulleys at the top of the column. As the rover traverses the test area, the gantry follows to remain directly overhead, while the counterweight assembly moves vertically within the column to maintain a constant upward force that offsets a controlled fraction of the rover’s weight. The five ft vertical travel of the weight stack provides the necessary range to sustain constant tension during elevation changes such as ramps or uneven terrain. System control is achieved through a hybrid OptiTrack based tracking architecture. Infrared cameras continuously infrared tracking markers attached to both the gantry and the rover, and their three-dimensional positions are processed in real time using a control scheme that combines velocity feedforward with position based feedback. This approach enables the gantry to maintain alignment within plus or minus ten centimeters and offload force within plus or minus ten percent of a fifty pound target during mobility trials. Developed by repurposing existing South Dakota State University infrastructure, including an industrial gantry and OptiTrack motion capture system, MRGO provides a scalable, reliable, and cost-effective platform for Earth-based partial-gravity simulation and robotic systems validation.

Library of Congress Subject Headings

Roving vehicles (Astronautics) -- Testing. 
Roving vehicles (Astronautics) -- Design and construction.
Space vehicles.      

Publisher

South Dakota State University

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Rights Statement

In Copyright