NASA Mission Concept Academy Suspension System
Introduction
For my NASA Mission Concept Academy this fall, I was tasked with designing the suspension system for our rover moving forward. Being a third year mechanical engineering student I was excited to take the concepts I have learned throughout these years and finally apply them to something complex and intricate.
The rover, which my team coined Project Circe, was given the task to explore the Martian surface for pockets of water that future humans could use to sustain a colony on Mars.
First thing I decided to do was to sketch out the design and get a basic understanding of the forces that would be acting on the suspension itself, the issues that may arise when designing said system, and the potential parts and materials to be used.
As per the design constraints the rover has to be within a 100cm x 100cm x 100cm volume and have a weight less than 30kg. These design factors dictated many of the decisions made for the rover and those considerations will be seen throughout the document.
Schematic time
This first page was figuring out the dimensions of the rover itself. Some simple math to figure out the max climb height and angle of the rover. Along with that, potential wheel ideas and their benefits/drawbacks were also thought out during this page.
A big thing to consider was that many of the off-the-shelf components that NASA uses are extremely resilient and are used for a reason, so they were given priority when going through the design process -- hence the Traditional wheel design.
To experiment, a Nitenol wheel design was considered as well to test cutting edge technology and their feasibility for different missions. Once the first page was drafted, basic CAD sketches were made to verify the numbers found and to determine which design would work best.
Shown above are the prototype designs for the suspension system (90 degrees, 120 degrees, and 150 degrees respectively)
Eventually, the 150 degree design was the option that was chosen because of its low CG and potentially high climb. Once that was finished, other design factors were looked into to have a better understanding of how the suspension system would be manufactured, more reliable, and more convenient to the mission at hand.
This next page was more calculations and napkin math of the forces acting on the design to find the best design possible for the system. A lot these calculations were focused on the “camber” of the suspension system itself. Would it be better if the bars were more vertically oriented or more horizontally oriented? Eventually, it became clear that it was not too big of an issue and the camber of the bars should be just enough to allow the motors enough clearance to go through the suspension motion without colliding with the assembly or the chassis of the rover itself. After going through the design and fleshing out the components the next picture was the Version 1 design that was created. With more work, hopefully this design can be refined more through conversations with the engineering team.
This page on the left focused on a crucial design for the Rocker-Bogie system -- a differential. With the traditional method, a gearing system would be hooked up to a motor to ensure that both sides of the suspension maintained contact with the ground. Taking inspiration from Formula 1, a new Rocker-Bogie design would eliminate the gearing system and replace it with a torsion bar. The torsion bar is more compact compared to the traditional gearing system and has shown high reliability in Formula 1 so it was a design direction I wanted to consider.
The final design
Shown is the final suspension system design.
Overall, the weight of the assembly was calculated to be around 8kg (excluding motors)
Through hard effort of the team, we were able to make this entire package fit within the size and weight requirements of the academy. A 69 page report was produced and published to the NASA L’SPACE Academy. The report can be found on the line below.
