Final Report and Presentation!

After many hours of collaboration, problem-solving, and review, we are pleased to share an overview of our final product, as well as our final report and presentation. Enjoy!

Summary:

In theme with its musical name, Team Circle of Fifths has developed the “Pian-Yo-Yo” as a way to marry the team’s shared interest in music with sleek mechanical design. The Pian-Yo-Yo’s central feature consists of 20 black and 28 white keys that snap-fit into each other and the yo-yo body. While these interlocking sets of keys are meant to catch the user’s eye, additional design considerations for how the yo-yo would play were made as well. Unlike most other yo-yos seen in 2.008, the Pian-Yo-Yo was developed for advanced play functionality. The use of a butterfly design for the body and a bearing in the central joint enables the yo-yo to continue spinning while at the bottom of its flight. Lastly, the Pian-Yo-Yo will sit on a thermoformed grand piano. Together, the various elements of the Pian-Yo-Yo combine form and function in complete harmony.

The Pian-Yo-Yo is an unresponsive performance yoyo with a C-size ball bearing at its core and a silicone O-ring response system. Each half consists of four parts: the main body, the snap ring representing the white keys, the press fit black keys, and the silicone O-ring. The main body is overmolded over two extra parts: the axle nut and a carbon shim for weight.

The snap ring and main body have a 0.01” interference and 0.15” length of engagement, which gives a very tight fit that can withstand drops. The black keys part presses into the white keys with 0.005” interference and 0.0625” length of engagement. In order to prevent rotation, there is a small notch on the inside face of the black keys that aligns with a slot on the white keys.

The two halves are connected by a ⅝” long 8-32 threaded rod which passes through the C-size (¼”x½”x3/16”) ball bearing. The bearing is press-fit onto a small lip in each half, keeping the ID attached to the yoyo while allowing the OD to spin independently. The bearings we chose have a concave outer surface, keeping the string centered in the gap. This prevents friction between the string and the body, allowing the yoyo to spin for longer.

When fully assembled, the yoyo is 2.22” in diameter and weighs approximately 70g. This is at the upper end of the optimal weight range, but we were limited by the weights of available carbon shims. Keeping with the piano theme, we designed a piano-shaped thermoformed stand that the yoyo sits comfortably on. The stand was thermoformed over a 3D-printed die that was printed using the SLA method.

Overall Thoughts and Analysis of Final Product:

We’d like to first thank our lab section peers and leader, Joseph Wight, for all the laughs, insights, and time we shared together. Throughout the course of this class, we have learned a valuable set of lessons that have reshaped our design process and how we strategically approach challenging decisions. The experiential learning process that this class is based on gave us valuable insight into effectively applying concepts learned in the classroom to more realistic settings.

Overall our production yoyos look great and function as expected. We were able to get a very smooth finish on the body of the yoyo, and with the extra weight from the carbon steel shims the yoyo feels good in the hand. In terms of assembly, the pieces fit together securely and nothing feels fragile about the build. Every yoyo is balanced while spinning which shows that we were able to achieve consistency throughout the production part runs. One difficulty we ran into while assembling the yoyo is that the snap fit of the white keys onto the body was very tight, and our measurements shown above indicate this is because the interference of the feature between the two parts was 0.024” rather than the expected 0.01”. This made it harder to snap each yoyo together, but with the 0.15” length of engagement there is no worry of the two pieces coming apart. For the other press fit, between the black keys and the white keys, the interference was about the 0.01” we expected but the fit is not as secure as the body/white keys fit because the length of engagement is shorter. Due to this, if the yoyo is dropped from sufficient height or thrown at the ground the black keys will pop out.

The yoyo bearing and response system works just as planned, with the bearing pressed onto a stud so the ID spins with the yoyo body and the OD free to move separately. This allows the yoyo to “sleep”, or spin freely at the end of the string. There were a couple yoyos that did not have enough room for the bearing to spin, and those immediately returned to the hand like normal yoyos but did not function in the way we wanted. The O-ring response system allows the yoyo to bind back up the string, but we found it to be slightly slippery at first and works better after being broken in.

If translated to mass production (such as alternative operating space, contracted performance tooling, robotics within a factory design etc.), several of the issues above could be addressed. The high interference of the body and white keys snap fit actually makes the yoyo more solid, and if they were being machine assembled the extra force needed to snap the pieces together is worth the better product. For the white keys and black keys press fit, the length of engagement could be extended or glue could be used for mass production. To address the bearing spin issue, the design would have to be revisited in order to give the bearing more space to spin, and industrial machines would hopefully be able to produce more consistent parts. And for the O-ring response issue, a stickier compound such as flowable silicone could be used to give a snappy response out of the box. As it stands we believe we made the best yoyo possible in the given time, and hope that more groups will take interest in similar unresponsive, advanced yoyos in the future.

Team_Circle_of_Fifths_Final_Report.pdf

Download PDF • 2.56MB

Link to view final presentation recording: https://www.dropbox.com/s/59gdak553opl2ht/Team%20A1%20Circle%20of%20Fifths%20final.mpeg?dl=0