SENIOR CAPSTONE (DESIGN II)

Developed an electro-mechanical smart phone case which actively protects against drops by deploying spring loaded rubber bumpers at the corners of the case when free-fall is detected.

CARNEGIE MELLON UNIVERSITY

MECHANICAL ENGINEERING

SPRING 2017

CHALLENGE

"Develop skills for working in teams, working with open-ended problems, identifying needs and opportunities, and making appropriate engineering assumptions."

SOLUTION

Our team of six developed an electro-mechanical system to protect a device from a sudden drop by deploying bumpers when the case detected a fall. These bumpers extended out from the corners of the case and rotated a quarter turn in order to protect the front, back and sides simultaneously.

PROTOTYPE ZERO

As the most experienced with electronics on the team, I developed a quick-and-dirty electronic prototype to test the feasibility of the project. This prototype consisted of a micro-controller, a gyroscope, an accelerometer, a small display, a battery, and was housed in a custom aluminum enclosure made on a CNC Mill. The aim of this device was to show our team the outputs of the sensor, and determine if detecting free-fall with accuracy and without false detection. Later, I incorporated a micro-SD card and updated the firmware to allow our team to log data live from the sensor during drop tests and analyze that data  in Matlab.

DROP TESTING RIG

Our team determined that we needed a consistent method of testing out our design iterations. To answer this need, I designed and fabricated a drop testing rig using standard and custom components. The rig allowed us to drop test our designs and quantify their performance relative to the previous iterations. Higher drops were simulated by adding weight to the drop carriage and we simulated different ground surfaces by putting them on top of the aluminum base. We attached the test subjects to a matrix of threaded holes in the carriage.

CNC MILLED BUMPER MOLDS

After several iterations, we determined that we needed to manufacture our bumpers from a more flexible material. Based on our research, we determined a two part urethane rubber would be best for the application. To make the molds for these bumpers, I started with the CAD models, and used them as a 'form tool' to hollow out the mold cavities in the mold halves. Next, I added the neccessary tapers and filling geometry required to make the molds function as we wanted. Finally, I used MasterCAM to create the CNC tool paths. Lastly, I hand-finished the molds to achieve the smooth surface finish.

PORTFOLIO

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