With the revolution of bicycle culture seen in recent years, cycling has become an increasingly popular hobby worldwide. Many of these novice to professional cyclists are interested in monitoring and improving their mobility and ease of transportation methods, but there is a lack of adaptability among manufactured racks. The goal of this design project is to create an adapter that can be inserted into 2 inch or 1 and ¼ inch trailer hitch receiver and can hold a Thule sidearm bike rack. The Thule sidearm bike rack is design specifically to be used with a roof rack, however many people have a hard time lifting a bike onto the roof of a vehicle and need an easier way of transporting a single bicycle. The solution is to take the Thule roof rack and move it to a lower, more easily accessible location. The trailer hitch makes an easily accessible and compatible location. Being able to transfer the Thule roof rack from roof to trailer hitch and back is desired, therefore there should be absolutely zero modification of the Thule roof rack itself. A number of different concepts for accomplishing this task have been reviewed and one design has been chosen to be moved forward into the manufacturing stage.
The purpose of the Adapt-A-Rack (AAR) is to create a system that can hold a Thule Sidearm roof rack that can be inserted into a 1¼ or 2 inch square receiver. This design allows for a fundamentally strong yet lightweight rack that can secure a bike onto the receiver of a car. The AAR allows a user to carry a single bike with a small outward footprint, and retain maneuverability of their vehicle. The AAR allows a user with multiple vehicles to use the same roof rack system on either the roof or receiver of the car. Since the Sidearm is mounted parallel to wind forces on the roof, the surface area is reduced as compared to the transverse orientation. The AAR accommodates this extra load by incorporating multiple boxed structures and an additional wind brace.
The AAR brings more functionality to a standard Thule Sidearm roof rack and allows for a simple, compact bicycle transportation setup. AAR can carry a single bicycle with minimal footprint, maintaining vehicle maneuverability. Mounting the AAR requires no modification of the Thule Sidearm. To allow user access to the rear of a car, the AAR can rotate 45 degrees from the locked position. To achieve this a single hand actuated latch is utilized, allowing for greater control when tilting the bike. These features make the AAR a unique product with a host of capabilities in transporting a single bicycle efficiently. In order to fulfill the design requirements, aluminum was chosen as the main material due to its strength to weight ratio and ease of manufacturability. The strength of the boxed structure enables a thinner plate to be used. A thickness of 1/8th inch for the structure and 3/16th inch for the bushing surfaces will provide enough torsional resistance and still maintain a lightweight design.
The design that we have chosen has a large amount of assembly involved in its fabrication, and only a few very critical points where failure could occur. Therefore, only a small section of the adapter design needs to be built and tested. The proof of concept will only need to involve those two parts of the rack to test the radial twisting of the beam and plate with the Thule rack attached. The Proof of Concept will be the upper portion of the AAR. Radial twisting of the adapter can lead to fatigue and eventual failure, also twisting will put excess stress on the Thule rack itself possibly causing damage to the roof rack. The Adapt-A-Rack design excels in meeting the quantitative design specifications for: trunk access, weight capacity, lightweight design, footprint and aesthetics. By incorporating a pivoting mechanism the design allows the bike to be rotated 45 degrees away from the rear of the vehicle, which allows access to the user’s trunk. The angle of pivot is limited by an internal stop, and a locking mechanism is used to hold the bike in a vertical transport position. Because the hitch mounted receiver is below the 20 lb maximum weight it can be easily maneuvered by an average user. The AAR is 12 inches wide by 4 inches high and can be adjusted to stick out 10 inches to 16 inches from the receiver. The adjustability of the footprint is provided by utilizing multiple hitch pin holes to set the desired rack location. This provides the ability to customize the footprint of the rack to meet each consumer’s needs. The width and height of the design were chosen to have the smallest possible dimensions while providing sufficient structural rigidity.
Ethical and Safety
The ethical and safety concerns that arise with the use of the AAR are the weight of the system and its capability to hold a bike safely. The AAR team will always strive to meet these demands and overcome any consumer concerns that may arise throughout the fabrication and testing processes. The AAR is designed to be lightweight so that any user can handle the system without considerable strain. The AAR can be easily maneuvered and follows the design foals to ensure the user can safely attach their bike to any vehicle for transportation. However, the other concern is the AAR’s capability to hold the owner’s bike securely to the vehicle. This issue is always being addressed, and multiple tests will continue to be run on the AAR throughout the design synthesis portion of the project. We will also continue to run future tests to verify our previous results from the Proof of Concept.
FABRICATION & TESTING
Cutting of the Adapt-A-Rack parts is done in the Palmer Engineering machine shop. First the sheet metal is measured and scribed for all parts with .25″ extra material for precision milling. Next the band saw is used to rough cut all the individual rectangles for parts. With roughly cut rectangles, each with at least a .25″ extra material on all dimensions, either the CNC or manual mill is used to precisely cut each part down to the correct size.
Once all parts were precisely cut on the mill they were given to Ryan who took the pieces to the shop and TIG weld everything. To do this Ryan used a jig to hold the parts to be welded in place where he tacked and then fully welded the parts getting the Adapt-A-Rack ready for final assembly.
Multiple tests were run on the Proof of Concept to verify the functions of the AAR. The functions that were needed to be verified were the strength and stability of the AAR. The torsional and bending strength was tested, as well as the locking pin stability while engaged. One of the tests was to take the PoC and twist it with a torque wrench in order to find the max torsional strength of the rack. A secondary test will bend the rack in order to confirm that the bending strength of the box structure is sufficient. Finally, the functionality of the locking pin mechanism was tested to ensure ease of use. If the PoC passed these specific tests, and the design decisions for the AAR have been verified and as designed now is adequate. The Thule Rack bolts directly to the upper portion of the AAR, and experiences the most twisting load. This twisting load is the most difficult to design for, and most important. This section of the rack will consist of ⅛ inch sheet aluminum for the top, front and back, and 3/16 inch sheet aluminum for the sides. Shown below are the theoretical computer analysis, and the result produced from the actual testing.
The AAR is designed to create a system that can hold a Thule Sidearm roof rack. The final design is strong yet lightweight and can secure a single bike onto a 2 or 1.25 inch receiver of a vehicle. No modification to the Thule Sidearm is required to seamlessly move from receiver to roof. Aluminum, with its high strength to weight ratio, was a perfect material to fulfill our design requirements. The multiple boxed designs has proven to withstand the harshest forces in both the Proof of Concept and the Prototype testing phases. The AAR brings more functionality to a standard Thule Sidearm roof rack and allows for a simple, compact bicycle setup that takes the guesswork out of bicycle transportation.
ABOUT THE TEAM
Ryan Gutknecht, Cameron Bender, Alexander Lyons (Team Captain), Steven Fuller, and Graham Leese
Every product has a hard working team behind the scenes. The following names are the group member that made Adapt-A-Rack possible.
Alec Lyons – Team Captain
Alec Lyons is a Senior Mechanical engineering student at the University of Nevada, Reno. He is on schedule to graduate in the spring of 2014 with a bachelor’s of Mechanical engineering. He has experience with metal fabrication, engine maintenance, and large scale LED displays from his past experience and work at Dynamic Digital Displays.
Steve Fuller is a Senior Mechanical engineering student at the University of Nevada, Reno. He will be graduating in May of 2014 with a bachelors in Mechanical Engineering along with a minor in physics. He has experience in reverse engineering and electronic meterology from his summer work at Kadan consulting.
Graham Leese is a Senior Mechanical engineering student at the University of Nevada, Reno. He is pursuing minors in both physics and unmanned autonomous systems. He will be graduating in the spring of 2014. He has experience in aerospace manufacturing from work at Exotic Metals Forming Company.
Cameron Bender is a Senior in the Mechanical engineering program at the University of Nevada, Reno. He will be graduating in the spring of 2014 with his bachelors of science and a minor in physics. He has experience in manufacturing and aerodynamics from working at Digital Solid State Propulsion.
Ryan is a engineering student at the University of Nevada, Reno on track to graduate May 2014. Ryan has experience in welding and has many understandings of a fully function machine shop. His understanding of design process and constraints provide a huge advantage to Adapt-A-Racks manufacturing capability.