Michael Andrus, Department of Mechanical Engineering
Introduction
My intent in applying for the grant from the BYU Office of Research and Creative Activities was to obtain financial help to design and build a jogging stroller that could easily convert to a bicycle trailer. Currently, there are a variety of bicycle trailers and jogging strollers on the market. Many of the trailers convert to strollers, but are awkward and unmanageable as such. None of the strollers I have seen can convert to a trailer. I felt that a small manageable stroller that converts to a trailer is in demand. In addition, I wanted to include an added feature that was not available. The stroller would include a suspension system to provide comfort and safety for the passenger. The task was intended to be a learning experience to collaborate with the instruction I had received in the classroom. I would be able to apply the engineering process to a project of personal interest, and in so doing gain a better understanding of it.
The Engineering Process
The engineering process is the evolution of an idea into a reality-a tangible mechanism. When I began the project, I understood the engineering process to be a linear and logical sequence of events. Throughout the process I would wear the hats of each member of a product development team-consumer, engineer, manufacturer, and marketer. First, I would design a marketable product I felt a customer would want and draw the plans/pattern on the computer with dimensions, tolerances, and other specifications. I would then take the plans to the machine shop and the pattern to the sewing lab and produce a working prototype. Next, I would test and evaluate the prototype and determine what changes needed to be made. Accordingly, I would redesign the stroller and produce a second prototype that would be ready to market.
Design
Before plans could be drawn and parts made, I had to gather and organize information and ideas. As a customer, I had to determine what I wanted in a stroller-size, comfort, safety, adjustability, ease of use, carrying capacity. Knowing what the customer wants gave me, as an engineer, a list of specifications to consider throughout the design process. For example, knowing the carrying capacity, I can make decisions about the size and material of the tubing etc. Each consideration becomes part of the design.
As an engineer in the design process, I had to identify some of the possible solutions for each specification then determine which would be the most practical based on simplicity, cost, and manufacturability. With these solutions in mind I spent many hours in the computer lab converting ideas and sketches into working drawings. As drawings progressed, the design began to evolve. Areas where I had clear images in my mind of what I wanted often became cloudy as I tried to draw and finalize them. I found myself backtracking and re-evaluating the specifications and needs versus wants of the customer. Small changes as well as some dramatic changes in the design were necessary. Other areas where I was searching for final solutions resolved themselves almost effortlessly.
Manufacture
I had decided that the first prototype would be to put together with removable joints. It would fit together like Tinker Toys and be adjustable. This allowed me to change various dimensions and aid the redesign phase. I went to the machine shop at BYU to start the manufacture of the stroller and soon realized I had neglected to consider the difficulty of the manufacturing phase during the design phase. The joints I envisioned looked great on paper but would have been extremely difficult to machine. I realized I would have to change the design, so I improvised and started machining parts that would work. I then realized that the engineering process was not always a linear sequence but sometimes a random and nearly chaotic web. In my mind, while I was machining, I was redesigning, modifying specifications and considering customers’ needs almost simultaneously. The seat design also changed and evolved as I sewed. Although the goal remained constant, the design continued to evolve.
Prototype I
The first prototype was completed at the end of April 1995. Functionally, the stroller works well. I am pleased with the suspension; it is simple yet effective. The suspension is adjustable so that I can easily determine the best spring stiffness for further designs. The stroller is sturdy, light and comfortable to use. Aesthetically, the prototype leaves much room for improvement. This is due to the rough joints and poor seat design. Also, the trailer conversion design has yet to evolve. One might say it is still a single cell organism.
Prototype II
I am currently working on the second prototype, the next step in the evolution of this design. The frame, rather than being pieced together, will be one continuous tube. In order to bend the tubing with accurate angles, I am making a tool to bend the tubing. The tube bender will be more precise and controllable than other benders available in the shop. As a result of the single tube design, there will be fewer joints. They will be less bulky and many will be welded. This will improve aesthetics and decrease weight. The seat will be narrower and will attach more securely to the frame.
Conclusion
Athough the design will continue to evolve, my goal will remain the same. I feel the second prototype is becoming a well designed, marketable product. I look forward to continuing my work on the project and witnessing its evolution.
By far the greatest success of this project has been the candid, personal understanding I have gained of the engineering process, and the satisfaction that comes from seeing my ideas become a reality.
The detailed report I submitted to Dr. Joseph Free can be obtained from the Office of Research and Creative Activities.