MIE.21 – Lunar Rover Digging Mechanism for NASA Robotic Mining Competition

• Brian Dompke
• Jon Garcia
• Matt Meyers
• Marissa Mungia
• Adrian Rahardja
• Joseph Stiso

The NASA Annual Lunabotics Robotic Mining Competition (RMC) is a student-led competition designed to educate students in the application of NASA Systems Engineering. This project follows the plan and development of the ATLAS rover designed to excavate, collect, and deposit simulated lunar gravel/rock. The goal of the competition is to navigate through a simulated lunar surface pit filled with craters and boulders, eventually to an area where the robot can dig through a layer of regolith to gravel. The ATLAS team broke down the robot into two subsystems, mobility and excavation. This report will mainly focus on the design of the excavation subsystem. Three different design concepts were considered for the excavation subsystem: a bucket ladder, bucket wheel, or an auger. After researching concepts and performances from previous years and looking at which succeeded, the team found the bucket ladder to have a significantly higher success rate than the other designs. A bucket ladder behaves similarly to a conveyor belt system which is comparable to the behavior of an escalator. An FMEA analysis was conducted to examine possible failure modes and risks of the digging mechanism during the team’s design process of the prototype. The FMEA analysis considered the following defects: limited mobility, cracking or fracture, breakage, loss of power, and getting stuck in regolith or gravel. Ansys simulations to predict the total deformation, strain, and safety factor were conducted on the digging bucket of the bucket ladder assembly and chassis frame to help determine if the design would fail during competition. Other types of testing and calculations were performed to find the proper constant force springs, DC motors that will power the ladder, and the mesh shape/size to filter the regolith through. Results of the Ansys simulations showed that both the bucket and chassis experienced little deformation and stresses when under maximum load conditions, similar to the conditions during competition. An issue the team was concerned with was the depth which the bucket ladder had to excavate. The gravel which the rover must reach is under a 30cm layer of regolith. To overcome this issue, the bucker ladder was designed to extend and retract using two linear actuators and constant force springs to hold a proper tension. Upon careful CAD design considerations, component selection, finite element analysis, and reliability testing, the team is confident that the final design meets the product design specifications for the digging mechanism.