The RISD Lunar Rover is a competition vehicle designed to compete in the NASA Rover challenge. The annual event sees teams race across a simulated extraterrestrial terrain, which consists of crates, boulders, ridges, inclines, crevasses, and sand pits. This time around our team decided that it was time to retire the old chassis and design and build a brand new vehicle from the ground up. The new design was lighter, more maneuverable, improved upon driver ergonomics, and incorporated better data collection, which included, among other things, a speedometer and a GPS unit. This was a ten months project with a team composed of roughly 18 people total.
Project Design Leader
Space Frame Chassis
When it came to designing the chassis, we decided to go with a space frame design. This setup enabled us to design a chassis that was very light, stiff, and strong. It also enabled us to easily install other components, like the differential and electronic, inside to confines of the frame, providing protection to the most delicate items.
Improving the ergonomics was something we wanted to focus on from the very beginning. The previous rover was suffering from compromises that were made in order to assure completion which lead to the riders being very unhappy with the comfort level of the buggy. We decided to stick with carbon fiber again but we redid the geometry to assure both comfort and strength.
One of the biggest challenges was to design a rover that could fold up and be placed within a 5 x 5 x 5 foot cube. The new rover was 8 feet long and in order to collapse it, we designed a single dual hinge to make the unfolding as fast as possible. This enabled us to get the buggy to stand vertically and fit within the box.
One of the big issues that needed to be solved in the new design was the rear drivetrain. Because the drivers faced two different directions the rover was equipped with two separate drivetrains. The problem was the rear driver had to peddle in the wrong direction in order to move the rover in the correct direction. In order to overcome this issue, we designed the drivetrain so that the normal pedaling direction would result in the wheel turning in the reverse direction.
In the very early stages of the development process we toyed around with a few different ideas. These included 3 wheel vs. 4 wheel designs, complete carbon fiber body, drivers sitting side by side, etc. We decided to go with a three-wheel design because of weight and stability. We also decided to put the drivers back to back so that we can keep the weight of the rover as centered as possible.
Designing the actually chassis was one of the most challenging aspects of the process. We start out by doing sketch models made from straws and hot glue. Once we had a sufficient enough idea of where we wanted to go we moved up in scale. We did some tests with PVC tubing and after we decided on a final size, we went to CAD to finalize the geometry.
At this point we had narrowed it down to 3 chassis. In order to get the lightest and strongest one possible, a finite analysis was conducted on each of the chassis to see which one would preform the best and which would be the lightest. This helped us finalize the chassis and then construction started.
The fabrication took place at the RISD shops. A large amount of the chromoly tubing was sourced from Cartesian tubing. The tubing was then cleaned and brazed using brass filler rod in order to assure maximum strength under racing conditions without worrying about annealing the steel.
Once the bulk of the brazing was done, we started fabricating other components like steering, suspension, wheels, seats, and drivetrain. We machined, molded carbon fiber, and 3D printed components in order to get the rover finished and ready for the competition.