Researchers at Universität Würzburg have developed a new Mars rover design featuring wheels modeled after the sandfish lizard, allowing the vehicle to “swim” through soft sand rather than relying solely on rolling. The project is part of the Valles Marineris Explorer (VaMEx) initiative, a program supported by the German Aerospace Center (DLR) aimed at creating swarms of flying, walking, and driving robots to explore the vast Valles Marineris valley on Mars.
Biomimetic “Swimming” Mechanism
The design takes inspiration from the sandfish lizard (Scincus scincus), a Sahara desert reptile that moves through granular surfaces by undulating its body from side to side. By replicating this biological strategy, the research team, led by Professor Marco Schmidt, created wheels that combine rolling with a wiggling, sinusoidal movement.
According to Schmidt, the wheels mimic the animal’s characteristic interaction with the ground to generate both lateral and longitudinal forces. This mechanism allows the rover to leave distinctive sinusoidal tracks in the sand, confirming that the swimming motion has been achieved. While conventional wheels often slip or sink on soft ground, these bio-inspired wheels use motion patterns and flexible shapes to distribute pressure more effectively.
Overcoming Traction and Sinkage
Navigating the Martian environment is challenging because loose soil and sand dunes can cause rigid wheels to lose static friction, leading to high slip ratios and sinkage. In such cases, a wheel may rotate without any linear displacement, potentially trapping a rover and risking millions in investment and years of scientific work.
The development of the swimming wheels involved an iterative prototyping process to solve early stability issues. Initial prototypes were narrower and heavier than conventional pneumatic wheels, which caused the rover to sink and reduced its controllability. Researchers remedied this by making the wheels wider and lighter, which increased flotation and reduced slippage. Following these adjustments, the prototype outperformed similar vehicles equipped with conventional wheels when traversing loose sand.
Testing and Future Integration
The rover, described as silver and roughly the size of a mini-fridge, has undergone testing in open terrain and controlled sand fields. These experiments were conducted in collaboration with the University of Bremen and the German Research Center for Artificial Intelligence (DFKI).
The Universität Würzburg team now intends to refine the wheel surfaces to improve traction on mixed terrain. Beyond physical hardware, the team aims to integrate software-controlled mobility. This would involve using real-time analysis of sinking, slippage, and terrain interaction to allow the rover to dynamically adjust its power distribution and wheel motion.
Comparison of Locomotion Systems
The development of these wheels exists within a broader context of planetary locomotion engineering. Different systems offer varying advantages depending on the terrain:
| System Type | Characteristics and Performance |
|---|---|
| Rigid Wheels | Efficient on flat, rigid surfaces but prone to sinkage and traction failure in loose soil. |
| Flexible Wheels | Used by the ExoMars rover to deform under loads, decreasing ground pressure on sand dunes. |
| Tracked Systems | Improve traction by spreading vehicle weight, but generally perform worse than multi-wheeled systems in rugged terrain. |
| Legged Robots | Represent the best locomotion system for rugged terrain. |
| Hybrid Systems | Combinations such as leg-wheels or wheel-tracks used to scout difficult areas. |
By combining the physical innovation of swimming wheels with advanced software algorithms, the VaMEx researchers hope to create an autonomous rover capable of navigating unpredictable Martian environments with greater efficiency and stability.
