Adaptive Tread Lateral Actuated System (A.T.L.A.S.): �An AI-Controlled Pneumatic System for Real-Time Lateral Wheel Expansion

Tikhon Kozlov

11^th grade, Urbana High School, Ijamsville, MD, USA

Project EBED01

All figures, schematics, and images are created by/taken by the researcher unless cited otherwise

Background

Two limit working positions of new variable-diameter wheel prototype. (Source: W. Zeng et al. / Appl. Sci. 2019, 9, 4631; doi:10.3390/app9214631)

Two-degrees-of-freedom transformable wheel based on a geared linkage mechanism. (Source: H.Yoon et al.,/ Scientific Reports, 14(1), 379. https://doi.org/10.1038/s41598-023-50804-y)

• Wheeled rovers are common tools used for planetary surface exploration. Wheels are essential to improve the rover’s mobility, trafficability, and obstacle-surmounting capability on unstructured surfaces.
• On soft terrain, conventional circular wheels sink and cause poor rover mobility. Therefore, to optimize mobility on soft terrain, growing research interest has focused on various unconventional wheels (1).
• By increasing the wheel’s diameter, a wheel can enhance the tractive performance and obstacle-surmounting capability of a vehicle.
• Various vertically expandable wheels that expand in either the axial or radial planes have been developed (2-4):

Variable-diameter wheels with torsion bar springs used in lunar rover (Source: W. Zeng et al. / Mechanism and Machine Theory 125 (2018) 240–258 )

Airless Origami Wheel combined structural principles of the "Da Vinci bridge" and origami design. (Source: Seong-Bin Lee et al,/Science Robotics (2025). DOI: 10.1126/scirobotics.adx2549)

Background (continued)

Vertically expandable wheels are often designed for specific, hard-ground conditions (like rocky or icy terrains), which might make them suboptimal for soft-ground conditions (like lava tubes or sandy dunes), requiring a tradeoff between compactness and floatation. Their key limitations include:

• Mechanical Complexity: Incorporating active, variable-diameter mechanisms increases the number of actuators, joints, and sensors, creating new failure modes in harsh, unmaintainable environments.
• Material Fatigue and Degradation: The repeated, intense deformation caused by traversing sharp, embedded rocks can lead to metal fatigue and reduced performance.
• Limited Load Capacity and Scalability: Expanding, airless, or mesh-based wheel designs are difficult to scale to accommodate the high weight of larger, manned pressurized rovers. Increasing load often results in uncontrollable stress on the wheel's internal components, such as spokes or loops.
• Reduced Speed and Efficiency: Vehicles equipped with complex, compliant wheels are often restricted to lower speeds, as high-speed operation could exacerbate structural degradation, requiring astronauts to spend more time traveling between locations.
• Vulnerability to Environmental Hazards: Lunar or Martian dust can infiltrate the mechanism, causing the joints of a variable-diameter system to lock; Extreme thermal variations and high radiation can cause traditional flexible materials (elastomers) to break down, necessitating the use of specialized, often fragile, metal alloys; Advanced mesh wheels can suffer from punctures or tears, as experienced by the Curiosity rover, which was launched in 2011 to explore the Gale Crater on Mars.

Problem Statement

Engineering Goals

• To enable the next era of autonomous extraterrestrial exploration, particularly in high-risk zones (like the surface of Ryugu or soft sediment on Mars) and on surfaces with variable conditions, there is an urgent need for research into different expansion methods

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• Therefore, research into alternative modes of wheel expansion and contraction is critical because current solutions are inherently unsuited for the variable terrains and the extreme conditions of extraterrestrial bodies

• Design a laterally-expandable wheel system in CAD software
• Assess the wheel system’s load capabilities using Finite Element Analysis (FEA) software
• Program an AI-powered image detection algorithm that can assess terrain qualities and make an automatic decision to laterally expand or contract the wheel
• Design a balloon-like bladder that will be inflated by a pneumatic pump system and can survive harsh space conditions

The surface of asteroid Ryugu, as observed by the Hayabusa2 spacecraft just before landing. Photo: MASCOT/DLR /JAXA

https://science.thewire.in/the-sciences/ryugu-uracil-life-space-origin/

https://www.jpl.nasa.gov/images/pia20168-high-dune-is-first-martian-dune-studied-up-close/

Materials & Methodology

Materials used:

• Personal computer
• Raspberry Pi 5 Core
• Raspberry Pi Camera Module 3
• Raspberry Pi AI Hat+ Module

Methodology:

• Use the CAD software OnShape to design components that assemble together to form a wheel with the ability to expand and contract laterally
• Validate the structural stability of the wheel assembly with FEA
• Program an AI algorithm that can recognize terrain types from images
• Embed the program into a Raspberry Pi AI Hat+ module.
• Test the AI algorithm by capturing images of real-world terrain using the Raspberry Pi Camera Module 3
• Conduct a mathematical analysis of the wheel system to evaluate its practicality

Results: CAD & Assembly

1. Main wheel: A model of the wheel, created in OnShape. 16” Diameter; 12.8” Width.

2. Laterally expanding spoke: Solid, revolving structure connected by a 90-degree spring hatch that forces it into a closed position (see 5). 6 ribs are used on the final wheel assembly (see 5 or 6). 0.2” Diameter; 7.93” Length.

3. Axle: Hollow tube around which the wheel revolves. Hollow to let air from the pneumatic system inflate the balloon-like bladder. 0.624” Diameter; 19.3” Length; 0.3” hollow tube diameter.

4. Balloon-like bladder: 1800 cubic-inch inflatable structure. Causes the ribs to expand when inflated, which increases the wheel’s width. Transparent for visibility.

5. Contracted assembly: The full assembly (bladder not shown for visual purposes) when the bladder is deflated, and the ribs are contracted.

6. Expanded assembly: The full assembly when the bladder is inflated and the ribs are expanded outward.

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Results: Finite Element Analysis

• This FEA run simulates the displacement (in meters) of the spokes when the bladder is expanded
• The spokes, which are made from Aluminum 6061-T6, each experience a uniformly distributed load (UDL) of 150 Newtons acting radially outward from the center of the wheel. This simulates the internal pneumatic pressure created by the inflated bladder
• The spokes only displaced a maximum of 1.72 millimeters, indicating a high structural integrity under the intended maximum load

Results: Balloon-like Bladder

Air

Bladder Structure:

Results: AI Algorithm

Results: Mathematical Analysis

Mean Maximum Pressure:

Theoretical Maximum Displacement:

Safety Factor:

Summary & Conclusions

Future Directions

• Create and test a wheel prototype to experimentally verify the results of the current project
• The construction of an expandable wheel on average costs between $100,000 and $250,000, and testing the wheel requires access to a laboratory where space conditions, such as no atmosphere and varying gravity, can be tested. Therefore, implementing this research in a facility with equipment such as vacuum chambers, artificial gravity centers, and radiation testing facilities is the next step

Summary

This project designed a laterally-expanding wheel that expands its width to suit the terrain it is traveling upon. The wheel uses a pneumatic pump to inflate an advanced balloon-like bladder that radially pushes out spokes to hold the bladder in place, thereby expanding the wheel’s width by half its diameter. An AI-powered terrain-recognition software automatically activates the pump to contract or expand the wheel. Simulation results and mathematical validation indicate that this wheel can be used on future rovers sent to explore extraterrestrial bodies.

Conclusions

• The FEA showed a slightly higher displacement (1.72 mm) than the perfect mathematical formula (1.39 mm). This is expected because the FEA accounts for the slight flexibility of the wheel itself, whereas the formula assumes the wheel is infinitely stiff. This 0.33 mm difference, therefore, proves that the simulation is realistic and the spokes can handle a 150 N load without experiencing plastic deformation.
• The materials of the bladder ensure efficient pneumatic expansion and
• The AI Algorithm works for detecting terrain types and is easily scalable
• The mathematical validation confirmed an aerospace-grade Safety Factor of 1.414, demonstrating that this autonomous, laterally-expanding wheel is a viable solution

References

1. W Zeng, F Gao, H Jiang, et al. (2018). Design and analysis of a compliant variable-diameter mechanism used in variable-diameter wheels for lunar rover. Mechanism and Machine Theory 125, 240–258, doi: https://doi.org/10.1016/j.mechmachtheory.2018.03.003.
2. Zeng W, Xu G, Jiang H, Gao F. (2019). Development of a Novel Variable-Diameter Wheel. Applied Sciences. 9(21):4631. https://doi.org/10.3390/app9214631
3. Yoon, H., Kim, S., Park, I., Heo, J., Kim, H. S., & Seo, T. (2024). 2 DOF transformable wheel design based on geared 8 bar parallel linkage mechanism. Scientific reports, 14(1), 379. https://doi.org/10.1038/s41598-023-50804-y
4. Seong-Bin Lee et al, (2025). Soft deployable airless wheel for lunar lava tube intact exploration, Science Robotics. DOI: 10.1126/scirobotics.adx2549
5. Lee, D. Y., Kim, S. R., Kim, J. S., Park, J. J., & Cho, K. J. (2017). Origami Wheel Transformer: A Variable-Diameter Wheel Drive Robot Using an Origami Structure. Soft robotics, 4(2), 163–180. https://doi.org/10.1089/soro.2016.0038