Design and Fabrication of a Mars Rover Four-Wheel Rocker System

In the University Rover Challenge (URC), teams from across the globe design and build rovers to compete at tasks that a rover might encounter on Mars, such as long-distance communication, scientific testing, cargo delivery, and equipment servicing. Robonav, a team from the Georgia Institute of Technology, participated in this competition and qualified for the on-site challenge for the first time in 2024. On an interplanetary mission, every pound of weight is critical. Saving mass allows for more complex designs with greater functionality. Therefore, Robonav chose to modify the rover (Wall-I) to switch from a six-wheel rocker-bogey system to a four-wheel rocker system. The transition would allow for many benefits. It would decrease weight and required power by removing two wheels and their attached legs. It would also make the system simpler from a mechanical and electrical perspective. In addition, switching to a four-wheel system would allow Robonav to transfer the differential bar from the top of the Wall-I's chassis to the back, freeing space for the electrical connections in the chassis. To begin this process, research had to be done into the various forces and stresses at play that would change with the modified wheel system. A literature review of existing designs revealed several equations that could be used to calculate optimal parameters for the design. After a mathematical model was put together, the design was developed in SolidWorks. It was iteratively adjusted to achieve equal or better clearance as the previous design while retaining stability. There was also a strong focus on reusing as many components from the previous design as possible to minimize costs. At the conclusion of the design process, many of the parts were made as low-cost trial alternatives through 3D printing. Once the design was verified, all of the parts were machined out of carbon fiber and metal, and the full system was assembled onto the rover. After completing the assembly, the team was able to test the new system and found that installing legs at 90-degree angles allowed for greater clearance while traversing obstacles. In addition, the decreased weight allowed more of the mass to be allocated to the arm and end effector. In addition, the change in the system did not significantly interfere with overall stability. Therefore, this study has interesting implications for the designs of rovers for use on Mars. While the more common six-wheel rocker-bogey design is currently favored, for less extreme terrain, it could be very beneficial to consider a four-wheel design.