Multidisciplinary Senior Design (MSD) Project
Work Completed by: Ryan Henry in collaboration with teammates.
This multidisciplinary project was completed as part of the senior year design project at Rochester Institute of Technology (RIT). The aim of this project was to progress through a full project development cycle with the purpose of creating a prototype rover for a proposed upcoming mission to the (16) Psyche asteroid. The team was composed of two Electrical Engineering (Robotics Concentration) students, a Computer Engineering student, a Mechanical Engineering student, and a Mechanical Engineering Faculty advisor.
Team Composition
* Ryan Henry [me](EE) - Purchasing agent, Fill in Mech-E
* Electrical Engineer (EE 2) - Project Manager, Fill in CE
* Computer Engineer (CE) - Mediator
* Mechanical Engineer (Mech-E) - Communications
* Faculty Mechanical Engineer - Consulting
Initial Planning
Initially the senior design project taken on by the team was not for this particular task. Originally the design stage was largely made up of design work for a project to design a prototype boat to be used by NASA to locate astronauts that have returned to Earth and landed in the ocean. Due to miscommunications from RIT, NASA, and the team, this idea was scrapped and led into the project of the rover prototype.
In the initial design and secondary design phases that took place during the first half of the Fall semester Senior year were intended to bring concept generation and feasibility analysis to the forefront of the project. Many ideas were analyzed for feasibility in the conditions known. Using the minimal knowledge at hand about the surface of (16) Psyche, ideas of a rover resembling various animals were proposed in order to bring some novelty to the rover design. These included inchworms, spiders, ants, alligators, snakes and more. Also here were more classic ideas such as common wheeled rovers and tank tread rovers. For various reasons, mostly pertaining to reliability, many of these ideas were scrapped.
Basic Design
Arriving at a potentially viable solution, some initial plans were implemented in 3D modelling with design functionality in mind. While the shape was not appealing, the functionality was present. In this design was a 360°-degree Lidar scanner for navigational purposes, six wheels on a rocker bogie suspension designed to maintain maximum points of contact and therefore stability of the overall system, articulated arms to correct rollover situations allowing for improved terrain adaptation, and an autonomous internal sliding weight system designed to adjust the center of gravity for further stability.
Wheels for this rover were custom designed to improve traction in the assumed surface material of the asteroid which is believed to be fine sand and small rocks with a solid iron-based metal layer below.
Secondary Design after scope reduction. Articulated arms reduced to movable stabilizing arms.
Final Design
The final design involved minimal overall changes from the previously mentioned design. Primary differences involved changes to the width of the wheels to reduce printing time to approximately 25% of the original and the navigational Lidar system was converted to an Xbox 360 Kinect system due to vertical vision limitations presented by the planar 360° Lidar that was accidentally purchased. Also included in this design was an improved and simplified system to increase stability in the chassis by utilizing a differential gearbox between the largely isolated axles.
While original scope was reduced significantly due to several factors such as budget, part availability, and time, the final result achieved and exceeded all original design requirements. Among these were the ability to traverse hills up to 60°, maintain stability and rollover prevention exceeding 70° of lateral tilt, and recognition of objects in the path of the rover within the range of 2 to 14 feet. These exceeded initial design specs of 32°, 25°, and 4 to 8 feet respectively.
Execution
Combining Machining (for chassis assembly) and 3D printing
(for custom part mounting, electronics trays, and wheels) the
rover was assembled as seen in the images to right. Machining
work was completed in part by the team's Mech-E in RIT's
machining lab while the remaining machining and all 3D
printing was completed by me using various hand tools
and 3D printers.
For the needs of the project a custom battery pack was
designed and assembled utilizing 24 batteries per pack in a 6P4S configuration.
Also in final execution came an added design limitation introduced by available testing surfaces and building materials of the wheels leading to the use of an aerosolized rubber coating on the wheel fins and rims to add traction and mild protective properties minimizing wear and tear.
In order to maximize line of sight for the Xbox Kinect, a bracket was 3D printed to mount it to the front of the rover and keep it in place without limiting the ability to turn, a feature discovered through testing. This allowed a viewing angle significantly larger than planned.
Results
After eight months of work and several design revisions, the final product was put on display at ImagineRIT, an event meant to showcase the work of students across the campus frequently attended by major technology companies like Boeing, Google, Microsoft, Honda, Amazon, Lockheed and more. The result weighed 55 lbs. which was down from initial design weight estimates of 120 lbs. allowing for a smaller potential take-off rocket. While not a fully functioning prototype, many planned specifications were met. These include visibility of the navigation system, maximum tilts both forward/backward and side to side, potential payload capacity, and battery survival time.
Looking to future designs based on the prototype, there are design choices that could be improved upon. Many of the structural brackets and the differential gearbox were printed using PLA plastic. This would ideally be printed out of ABS in future revisions of the prototype in the budget does not allow for metal manufacturing as PLA is too soft to hold up to the rigors of testing. The suspension of the stabilizing arms could also be strengthened to improve stability as the current version is undersized for the needs of the rover.
Asteroid and Mission
The asteroid (16) Psyche Asteroid is an asteroid located in the asteroid belt between Jupiter and Mars and is believed to be composed largely of iron and nickel. Specifically orbiting approximately 3 times further away from the sun than Earth, it averages 140 miles in diameter and is among the largest asteroids currently known about within the asteroid belt. Due to its composition, it is believed to possibly be part of a broken planetesimal, a roughly city sized precursor to planet formation. The surface is largely unknown and unstudied but is believed to be largely composed of dust, fine sand, and small rocks with a hard metal crust underneath.
The mission, planned to launch in 2022, is planned to send a reconnaissance satellite orbiter to the asteroid in order to determine vital qualities about the asteroid mostly involving the surface qualities. This is in order to prep a mission to the asteroid using a rover that can take samples and send them back to Earth for studying. As large as this asteroid is and the material it is believed to be composed of, it is thought to be worth potentially billions or trillions of dollars. This does not include its potential intellectual and academic worth if it does indeed turn out to be part of a planetesimal as it could give insight into the formation of not only our planet but many other rocky planets throughout the universe.