About

Our nationally recognized faculty, researchers and professional staff are dedicated to excellence in research, education, innovation and service. Learn more about the individuals who make up the Department of Mechanical Engineering by visiting their profiles.

Research topics

• Computer Science
• Geology
• Engineering
• Mechanical engineering
• Artificial Intelligence
• Ecology
• Geography
• Biology
• Simulation
• Marine engineering
• Cartography

Selected publications

• Novel Robotic Fleet for Sample Recovery in Lunar Craters: A Concept of Operations

  IEEE transactions on field robotics. · 2025-01-01

  articleSenior author

  Exploration of extraterrestrial surfaces, such as the lunar surface, can prove treacherous for humans and robots alike, and requires highly specialized mobility platforms to ensure the success of a mission and the safety of any operators. However, these specialized machines may limit the overall scope of a mission by limiting performance outside a particular environment. Thus, for maximum capabilities, a team of distinct but complementary specialized robots and vehicles may be used to expand mission capabilities in lunar environments. In this paper, a concept of operations for exploration of a lunar crater from utilizing a collaboration between a wheeled rover, represented by the RAD Exploration Vehicle (REV) and a non-traditional spherical robot, represented by RoboBall II, is introduced. These robots are used as an analog for mission-capable robots such as NASA’s Chariot rover and the larger RoboBall III. Design of these robots, along with collaborative features and intended operational environments, is discussed. A controller for RoboBall to attempt controlled descent on slopes is presented. Further, a ballistic sample return module for collection and ex situ analysis of a sample from the bottom of a lunar crater, along with potential navigational mechanisms to facilitate efficient recovery, is presented. Finally, a mission analog using RoboBall III and the ballistic sample return conducted in a former quarry is demonstrated.

  PublisherDOI

• Design of Soft Outer Shells for Control of Large Spherical Robots

  IEEE Robotics and Automation Letters · 2025-10-02

  articleSenior author

  While soft-shelled spherical robots offer promising mobility and robustness for planetary exploration, large-scale, mission-capable robots present several design challenges. This paper presents the design, manufacturing, and performance evaluation of multiple soft outer shell iterations for RoboBall III, a large, pendulum-driven spherical robot. Shell geometry, material properties, and fabrication processes are systematically examined to understand their effects on mobility and control authority. Empirical results, including sphericity analysis, contact patch behavior, passive response, steer compensation fingerprinting, and agility demonstrate that minimizing shell asymmetry significantly improves steering performance. The final shell design achieves near-ideal sphericity and passive angle retention, enabling more predictable control with reduced input effort.

  PublisherDOI

• A Platform for Autonomous Lunar Rover Rescue

  2025-03-01

  articleSenior author

  When NASA's Artemis astronauts return to the Moon, they will bring Lunar Terrain Vehicles (LTV) to help explore and set up a permanent presence on the Moon. The astronauts will pilot multiple LTVs to help transport supplies, collect research samples, and survey the lunar surface. Each LTV is expected to do these same tasks autonomously while the astronauts are away. If an LTV was entrapped in lunar regolith, tip over while maneuvering, or break down from the harsh environment, there is currently no way of saving it. If NASA cannot save the stuck LTV, they will incur the cost of the LTV, the investment it took to transport a vehicle of that mass to the Moon, and the decrease in productivity while astronauts are not on the surface. This is a problem that must be solved before long term lunar automation can be feasible. We propose a solution to modify the current LTV requirements such that the robotic arm can autonomously use the on-board winch to save a fellow LTV from a lunar grave. In this paper, we present a system design comprising of a winch motor and robotic manipulator capable of autonomous use. A demonstration of our robotic manipulator utilizing a winch system autonomously is presented.

  PublisherDOI

• A Compact, Reliable, and Reproducible Termination Method for Synthetic Fiber Tendons in Humanoid Robotic Hands for Space Applications

  2025-12-01

  articleSenior author

  In the field of human spaceflight, humanoid robots that can interact with tools represent a valuable asset to long-term missions with transient human residence. To interact with their environment, due to form factor constraints, robots of this class feature tendon-driven robotic ‘hands’ as end effectors. One of the main failure points of robotic hands is the tendon terminations. The tendon terminations transfer the force of the grip and see high cyclic loading. Many studies focus on the max strength of these terminations but fail to study the performance over cyclic loading. This paper introduces a novel tendon termination that is compact, reliable, and repeatable. This is shown through repeated loading to a worst-case scenario lifting condition, as well as characterization of the ultimate strength of the tendon termination.

  PublisherDOI

• Empirical Contact Models for Soft Spherical Robots in Drake

  IEEE Robotics and Automation Letters · 2025-10-09 · 1 citations

  articleSenior author

  Accurate dynamic modeling of soft-shelled spherical robots is challenging due to coupled rigid–soft body interactions and pressure-dependent contact behavior. This letter presents a modeling strategy for an empirically tuned pendulum-driven inflatable spherical robot. The approach combines a rigid-body dynamics engine in Drake with non-conservative effects. The robot's rigid-body model is generated from a custom URDF and augmented with interchangeable joint friction modules. Three alternative outer shell contact models are also considered: Drake's native hydroelastic contact, a pressure-dependent injected stiffness–damping model derived from isolated shell experiments, and a rigid point-contact baseline. Shell dynamics are characterized in the steering direction using a custom locking fixture, yielding empirical pressure-related frequency and damping relationships to parameterize the models. Ramp descent experiments across multiple inflation pressures validate the framework, showing that an appropriate model reduces drive velocity prediction error compared to a rigid point-contact case. The approach enables modular integration of additional dynamic effects, supports data-driven parameter tuning, and provides a reproducible pathway for accurate simulation of soft spherical robots.

  PublisherDOI

• Robotic Space Simulator: Design and Characterization of a Test and Evaluation Platform for In-Space Robotics

  2025-03-01 · 2 citations

  articleSenior author

  In this paper we introduce the Robotic Space Simulator (RSS), a new testbed for in-space robotics using two 7-DOF Gough-Stewart platforms. The RSS was developed to simulate a spacecraft with a robotic manipulator approaching, grappling, manipulating, and decoupling from another spacecraft, fusing accurately simulated centroidal dynamics with real force-sensorized contact interaction and realistic visuals. RSS addresses many of the deficiencies of other physical simulation tools by operating in SE(3) with high payload capacity, increased precision and reachability, and without additional requirements such as waterproofing of test articles. The RSS was designed to enable the testing of full-scale flight articles with a workspace that permits testing of multiple spacecraft and full-contact interactions between them via robotic manipulator. In this paper, we outline critical design criteria to meet these requirements such as payload capacity and reachability, and sensor range and resolution. The RSS uses force-torque sensors on each platform to simulate full-contact microgravity dynamics between the spacecraft. The sensor design prioritizes measurement range, so that the effective platform payload is not limited by the sensor. With that constraint, we next prioritize sensor selection based on their measurement resolution to maximize sensing capability and simulation fidelity. In addition to design optimization, we present initial evaluation of the disturbance characteristics of the platform as measurable by the incorporated sensors. Additionally, we evaluate the inverse and forward kinematics solving capabilities and their impact on the Jacobian-based feed-forward controller. Next, we present the calculated workspace of each platform including their additional axes. Overall we find the physical design, layout, and sensing capabilities of the RSS to be suitable as a test and evaluation simulation platform for space robotics. We find there is no significant disturbance due to the platform actuators which minimizes the need for signal filtering. We find that the Jacobian is well-conditioned throughout the reachable workspace of the platform, and the forward kinematics numerical solver is 100% successful in an average of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$19.2 \mu\mathrm{s}$</tex>, which is well under the 4 m s period of the control loop. Finally, we present the workspace of the RSS platforms including their additional axes. We calculate the effective workspace of the simulator to be approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$250\ \mathrm{m}^{2}$</tex>.

  PublisherDOI

• Empirically Compensated Setpoint Tracking for Spherical Robots With Pressurized Soft-Shells

  IEEE Robotics and Automation Letters · 2025-01-08 · 5 citations

  articleSenior author

  Replacing spherical robots' hard shells with soft, pressurized tires has the potential to improve their off-road practicality immensely. This change leverages spherical robots as a simple and rugged solution to problems currently addressed using wheeled or tracked vehicles. Though numerous prototypes have been launched over the last three decades, there has not been a spherical robot that poses a serious contender to tracked and wheeled systems. Most prototypes are built with a hard outer shell for ease of construction and control. Hard outer shells fail to absorb the impacts from uneven terrain. We addressed this issue by constructing a one-of-a-kind spherical robot with a durable pneumatic, soft outer shell. Although a soft-shell is more desirable for locomotion, it introduces complicated, nonlinear shell dynamics that cause a more challenging control problem. This article presents an empirical model of the steady-state torque induced by soft-shell dynamics, developed using system identification and a model based on tire dynamics. We show how this model, which fingerprints the robot's contact dynamics, is incorporated into RoboBall's steering control algorithm to compensate for soft-shell effects, enhancing setpoint tracking and improving control performance.

  PublisherDOI

• Scaling of RoboBall: A Parametric Robot Family for Crater Exploration

  2025-03-01 · 3 citations

  articleSenior author

  Non-conventional robotic rovers have gained traction over the past several decades as traditional designs continue to struggle with steep crater edges and other extreme lunar terrain. One particular paradigm of interest in non-traditional rovers in recent years has been inflatable, pendulum-driven spherical robots. Previously, a 2 ft. (0.61 m) diameter spherical robot named “RoboBall II” was built and tested as an alternative rover proof-of-concept. Compared to legacy rover designs, this robot possesses several advantages, including environmental protection, robust operating orientations, and generous descent angle. Despite this, RoboBall II's relatively small size introduced many new challenges, including a lack of payload space. As such, RoboBall II's intended use is primarily as a research testbed and reconnaissance platform. RoboBall III, as a 6 ft. (1.8 m) diameter ball, addresses these challenges. With a 6 in. (0.15 m) diameter hollow annular region as the driveshaft, payloads akin to NASA's CubeSats in size could be fitted to the system for exploration or reconnaissance tasks, allowing RoboBall III to physically interact with its surroundings. However, with scaling comes many challenges. This article will discuss the effects of scaling on slope climbing performance, overall mass, component power requirements, and construction methods from RoboBall II to RoboBall III. Shortcomings between predictive models or derivations and practicality when physically building a robot of this class will be highlighted. These results will be utilized to optimize future RoboBall designs.

  PublisherDOI

• Robotic Space Simulator: Controls Implementation for Auxiliary Axes and Zero-G Dynamics

  2025-05-19

  articleSenior author

  The Robotic Space Simulator was developed as a physical simulation for in-space manipulation tasks. It incorporates external inputs to its dynamics simulation via force/torque sensors mounted to the 2 6-DoF Stewart platforms which compose its primary structure. Each platform is augmented with an additional degree of freedom in the form of an auxiliary axis - one in translation and one in rotation. Previous work has not effectively included the additional workspace provided by these auxiliary axes. Additionally, it limited the use of external force/torque inputs to the case of platform translation only because the external forces/torques due to platform motion and gravitational force were not removed from the sensor inputs prior to inclusion in the dynamic simulation. In this work, we address each of these limitations. We develop and test two methods of auxiliary axis control: Cartesian Workspace and Joint Cost-Function, and find that both methods are an improvement over the existing system. Additionally we develop and test a method for calculating the mass properties of hardware mounted to the force/torque sensors and a dynamics compensation method for this hardware. Using this technique we are able to effectively compensate for gravitational force in different platform orientations, and achieve zero-g behavior of the system.

  PublisherDOI

• Non-Invasive Six-Axis Force-Torque Sensor Temperature Correction &amp; Calibration Refinement with Application to the Robotic Space Simulator

  2025-12-01

  articleSenior author

  In this work we describe a method of reducing measurement error of force-torque sensors without any physical modification of the sensor itself. The sources of errors addressed include temperature variation, mechanical preloading, and application-specific sensing ranges. The methods described are generally applicable to commercially available six-axis forcetorque sensors, particularly those based on strain-gauge measurements. For each of these errors, the correction methodology described is applied to the Robotic Space Simulator force-torque sensor which is installed beneath a Universal Robotics UR20 manipulator. For this sensor, a model describing a linear relationship between temperature variation and wrench error is obtained and applied. Additional temperature model variation is briefly described, such as hysteresis, but these effects are not included in the described model. By not including these effects, the duration over which the model is accurate is reduced to several hours, which is more than adequate for typical use. Applying the described model, we are able to reduce the RMSE of the raw sensor signal by up to 85% in one axis and 50% averaged across all 6 axes. Additionally, we obtain a refined calibration matrix which more closely aligns the sensor output wrench with the expected wrench due to known loading conditions. This calibration refinement accounts for differences between factory measurement range and expected sensor usage conditions, such as a more limited measurement range in one or more axes. Additionally, it inherently corrects for any installation-induced errors from surface irregularities and fastener torques and any residual cross-talk error from the factory calibration. The calibration refinement is obtained using a linear regression between the sensor output wrench and the wrench expected due to kinematic conditions of the RSS and UR20. Applying the method results in an RMSE reduction of up to 99% in one axis and 92% across all axes.

  PublisherDOI

Frequent coauthors

• William Bluethmann

  Johnson Space Center

  12 shared

• Venkat Krovi

  9 shared

• Seth Hutchinson

  9 shared

• Nancy M. Amato

  9 shared

• Torsten Kroeger

  9 shared

• Fredrik Rehnmark

  Honeybee Robotics (United States)

  7 shared

• Myron Diftler

  7 shared

• Micah Oevermann

  Texas A&M University

  6 shared

Awards & honors

• Member, National Academy of Engineering – 2020
• University Distinguished Professor, Texas A&M University – 2…
• Thomas A Edison Patent Award, American Society of Mechanical…
• Robo-Glove, NASA Commercialized Invention of the Year – 2020
• Selected for Senior Executive Service (SES), 2016