The blazing brick
Fall 2022 - Spring 2023
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I worked through the design process with two Product Design and Manufacturing graduate students over the course of two semesters to research, design, troubleshoot, and fabricate a functional prototype of the Blazing Brick, an automated bike light that reacts to motion and ambient brightness. Being the only MechE in the group, I quickly realized that I had the least CAD and design experience so I had to adapt and pick things up quickly in order for our team to be successful.
We started by doing research on bike accessories to see what was already available on the market and didn't find any products or patents similar to the one we were proposing, so we continued forward and came up with a list of specifications that we narrowed down using survey results. Now knowing what we would have to fit into the device, we sketched design possibilities and chose the one below because of the flexibility offered by the large surface area of the top face.
Specifications:
Longer Battery Life (~10 hours)
Less Manual Input (Automation)
Adequate Brightness (800 lumens)
Forgiveness Mechanism (Solar powered backup battery in case the main one was not charged)
Secure, Theft-Proof Mount
Clear Battery Life Indication
Easy Mode Switching
IP65 Standard Weatherproofing
We broke the project into three subsystems: the main body, the electronics, and the one I worked with most intimately, the battery housing for the removable battery pack that would allow the user to leave the light on their bike when it needed to be charged. After researching snap-fit designs, waterproofing methods, materials, and injection molding requirements, I came up with my first design which was intended to house a LIPO battery. It consisted of three injection molded parts held together with a combination of cantilever and annular snap-fits, was waterproofed with gaskets, and had a cavity where the latch on the main body would catch to hold it in place. The battery pack (gray/yellow) and the main body (blue/red) are shown below (not to scale with respect to each other).
Having never designed a part for injection molding before, there was a lot I needed to learn if I wanted to make smart design choices. Below are some of the more significant problems I encountered and how I worked solutions to them into my design:
Overhangs
Originally, I thought both styles of snap-fit would pose a problem because of their overhanging geometry, but a technique called stripping, which is where the part is removed from the core while it is still warm, allows the part to flex out of the mold.
Wall Thickness
Walls that were too thick or uneven would cool in a way that would cause imperfections to appear on customer facing surfaces. Running mold flow analyses allowed us to predict the quality of the finish on the final product and make appropriate adjustments.
Tooling
While brainstorming design options, I learned about side actions and how they can increase tooling costs. Manufacturing the housing in three parts eliminated the need for side actions that would have been necessary had we only made it in two.
As the name suggests, the Blazing Brick was clunky and didn't fit comfortably on most bike handlebars, so we scrapped the whole thing and started over at the beginning of the second semester. We took this chance to switch from a LiPo battery to a Li-Ion battery due to safety concerns and the large amount of space it required and stacked the LEDs in a 2x2 formation rather than having four LEDs lined up horizontally in a row. This made the final product marginally taller and much longer, but halved the width which was the most critical dimension. We also moved features around on both the battery housing and main body to minimize the manufacturing cost by reducing the total number of necessary side actions.
In the case of the battery housing, we decided that using a side action to simplify the overall design of the battery housing was worth the tooling cost tradeoff. This change also solved the waterproofing issue we ran into where all three parts met. This left us with a total of fourteen parts with only four of them requiring a side action. We came up with two new two-piece designs (shown right) for the battery housing and chose to go with the L-shaped one to ensure the end user would have no doubt that the battery was being put into the light in the correct orientation.
With our design finalized, we produced manufacturing drawings using GD&T and began the prototyping process. We used a combination of FDM and SLA 3D printing for most of the components including both the main body and battery housing, the mounting system, the battery catch system, and the encoder knob while the gaskets, lens, and display covers were created with silicone molding and laser cutting. Once assembled, the light turned on and changed settings appropriately depending on environmental factors. I also designed the logo featured on the front of our model.
BatTop DWG_016.pdfBatBot DWG_017.pdfPage updated
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