Documentation of the design and fabrication process of RISD"s 2017 NASA Rover Challenge Entry
The basic rules of the competitions state that the vehicle must be purely human powered, be able to carry two people (one male, one female) over various terrains and obstacles. The vehicle must also be able to fit in a 5’ by 5’ cube, and wheels cannot be pressurized in any way, nor can it use any pre-fabricated components.
Using the design process of ideation and prototyping, we began with a series of incisive studies into the basic mechanics and ergonomics to define additional limitations. Combining the competition rules and our internal constraints created a comprehensive set of guidelines to inform our design process.
Low-fidelity studies led to more refined and functioning prototypes. The rover was then modeled in Solidworks to ensure proper fit and clearance between all components.
One critical aspect of the rover is weight, as it affects both its speed and the ease with which it can overcome obstacles. To address this issue, we turned to carbon fiber; not only is it have excellent tensile strength, but its also has one of the best strength-to-weight ratios. It made an attractive candidate for both the wheel, seats, and suspension.
The wheels were especially appropriate candidates to test out this material as it had to be built from the ground-up. Inspired by Cheetah blades, each of our wheels featured a continuous external rim supported by six ‘spokes’ which converged on a central hub. Much like a bicycle wheel, each of these spokes was tensioned to provide rigidity on smooth surfaces, but unlike bicycle spokes, they had a degree of compliance which acted as additional suspension.
The process which was used to create all the carbon-fiber parts is called resin infusion. It involves creating a mold of our object, on which we lay up the raw carbon fiber sheets and then placed in a vacuum bag. A vacuum is then used to draw in liquid epoxy resin, and thus ‘infused’ within the fibers. The resin takes time to cure, but it’s what gives rigidity and form, after which we can do the post-processing of part cleaning and post-curing, creating the final part.
Excepting the limited use of bike components, all other parts of the rover were custom fabricated using a range of processes, including machining, CNC, brazing, welding, and casting. Materials used included carbon fiber, chromoly steel tubing, aluminum and urethane rubber.