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Our goal for this project is to build a hand-cranked trike for a child suffering from Spina Bifida, a condition that limits their leg mobility. We are prioritizing functionality and safety above all else while ensuring that the product’s use is an enjoyable experience.
The family has requested that the modified walker:
Corresponding Technical Requirements:
This design was based on the current walker that Paul had. We chose it because we thought that he was already acclimated to the design and it would be a natural fit for him. Based on how this walker collapses, adding the foldable steps on the sides will not inhibit the walker’s ability to fold.
Two battery cases will be supported by chassis attached to the legs of the front two wheels. There will also be extension features added to each leg of the walker.
This design was chosen because of the adjustable height capabilities. It allows the user to use his arms for support and greater stability while in motion.
Since the base of this walker is a hollow square frame, a foldable step and battery chassis can be placed in the frame such that the chassis do not inhibit the child’s movement.
This design is advantageous because of the compact storage option. It is also more affordable and an easier to modify design than Concept Designs 1 and 2. The lateral movement is easier to control with this design as well.
Battery chassis would only have to be installed on the back two wheels, and the handles can be modified to allow front wheel steering.
After a discussion with the mother of the child, it was decided that instead of building a motorized walker like another group, it would be more beneficial to build an arm-controlled trike. The purpose of the trike is to give the child a functional toy to ride along with his friends that doesn’t require force from the limited mobility in his legs. Trikes that avoid the use of leg power are not readily available on the market, especially ones fit for a 3-year-old child. Due to this change of path about halfway through our journey, we had to be efficient with our time and make quick decisions. Through a lot of discussion and research and planning, we came up with a design that will fit the child and his family’s desires perfectly while ensuring safety.
Our design involves using a foot-pedal powered, young-child sized trike that is readily available on the market and making a series of alterations to it. The base trike will come with rubber tires and a metal frame to promote comfort and durability. We will start by removing the handle bar from the trike and replacing it with a hollow tube from a beach cruiser bicycle. This tube will allow clearance from the fork for the chain, which we will discuss shortly. Attached to the tube will be a bottom bracket shell, which will hold a 3-piece bottom bracket. This bottom bracket will be in charge of holding the 1-piece BMX crank, which, when handles are attached, will act as the pedals that will control the movement of the bike. Also attached to this handle apparatus will be a small sprocket. The small sprocket will hold a chain that goes all the way down to the front wheel via a direct drive cog. The direct drive cog will be placed between the fork and the wheel. To ensure the chain is secure and to avoid any safety hazards, a majority of the chain’s path from the small sprocket will be covered. The direct drive cog will not only allow the foot pedals to move along with the arms (this was requested by the mother), it also prevents the need of a hand brake. The bike will stop whenever the hand pedaling stops. For the foot pedals, we will use ones that are heel-supported and velcro-strapped. This will keep the child’s feet in place during use. Lastly, we will apply a steering stop to the base that will limit the turn radius of the handles to protect the chains and provide easier control.
This analysis focused on the reaction forces generated by the weight force on the seat.
This analysis focused on the maximum moment that could be potentially generated by turning the handlebars.
This analysis focused on the possibility that the ground pressure generated by the tricycle could be a potential concern for us.
The trike was built to be as easy and safe to use as possible. Some of the safety features include a seatbelt, pedal straps, heel support, and chain guard. While none of these things were necessary for the functionality of the trike, they assure that the child will be able to ride without being at risk of injury. Beyond this, it is just recommended that the trike not be used on steep hills; the trike uses a direct drive system, so if the trike were to begin rolling at a high speed down a hill, it would take extra force to maintain control of the hand-cranks.
This project was a major learning experience for our group. While we were able to accomplish what we set out to do in our original design, we achieved it in a much different way than anticipated. Despite us planning on buying everything that would be put on the trike, we ended up only purchasing the base trike, some bolts, a seat belt, a new chain, and an $8 donor bike from Goodwill. Instead of buying more, we designed and fabricated 13 parts out of metal, plastic, and acrylic through CAD/drawings that were implemented on the final design (we made a lot of parts that were not ultimately used). This was way more than our original plan of zero.
Overall, we were able to put a lot of the machines and tools in the shop to use throughout this project. These include a mill, lathe, drill press, belt sander, band saw, water jet, dremel, and many more. Being able to use a lot of these machines opened our eyes to the importance of designing to manufacturability. While these tools can do amazing things, there are so many things that are needed to be accounted for to make sure parts are made successfully. Whether it’s the placement of dimensions on a drawing, the size and lengths of bolts that are common/readily available, or the fact that bolt head dimensions are necessary in conjunction with the rest of a design, the only way to learn is to experience first hand.
We also learned how difficult it is to alter a manufactured product that isn’t designed to accommodate major changes. Because of this, we found ourselves building and adjusting parts without worrying about future creations. This method took a lot of time, but it left us with a better understanding of our trike than if we had taken a different route. If we were to redo the project with the knowledge that we have now, it would probably take us a week to complete instead of a few months.
Ultimately, this project was an incredible learning experience for all of us. It would be wrong of us not to mention the help we received from the guys at Caney Fork Cycles. We would check in with them regularly throughout the project to get advice on our design, and that helped immensely. We also couldn’t have done anything without the assistance and mentorship of Chris and Jeff in the machine shop. They taught us so much throughout the project and we would not have gotten as far as we did without them.
