Final design and results

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Our team decided on a UFO themed yoyo for our design.  The yoyo consists of 4 components: an injection molded base, an injection molded top ring, a friendly injection molded alien, and a thermoformed dome.  These 4 components make up half the yoyo, or one UFO.  Another UFO is attached with a set screw, an axle spacer, and two embedded hex nuts.  Adding a 44in string completes the yoyo.

The silver base makes up the most mass of the yoyo, and makes contact with all three of the other parts.  The top ring snap fits around the outermost ridge of the base, and the alien snap fits inside the center hole.  There is also a groove where the thermoformed dome fits during assembly.  Other aesthetic features of note are the keyboard and the outer ridges.  The alien’s keyboard was made using precise machining with a 1/32” end mill and the outer ridges required 3D machining to manufacture, which also produced tiny radial lines that resemble metal sheeting and help hide the injection molding weld line.

The top ring snap fits onto the base, has the same outer diameter, and is the same color, making the two look like one part.  The outer diameter of the ring and base are curved to eliminate a sharp edge and make the yoyo more comfortable to hold.  The 12 small protruding bumps on the top were machined with a 1/16” drill. The 6 larger holes on the outside were made using 3D machining, which like the base also produced tiny radial lines. Other than these aesthetic and textual features, the top ring also serves to securely lock the dome into place.  We dimensioned the inner diameter of the ring to fully constrain the dome when assembled.  This in addition to a very tight snap fit required us to use an arbor press to fit the ring onto the base.

For the alien we used trial and error to find the right mixture of green and glow in the dark plastic, and ultimately produced a nice light green.  He appears to be very friendly from inside the UFO, literally greeting the world with a smile and open arms.  We made sure that the antennae, the most fragile part of the yoyo, are short enough to avoid contact with the dome.  The snap fit between the alien and base is also extremely tight, making up for it only being 0.1 inch deep.  The alien mold was produced exclusively with 3D machining, which was necessary to make the odd shape.  The mold produces two aliens per injection molding cycle, reducing production time.

Finally, the clear dome is the last component of the yoyo.  It was produced by thermoforming and is pinned in place between the top ring and base.  Despite being made of thin plastic, it is extremely structurally solid due to its spherical shape.  It’s not possible for a person to bend it with his bare hands, and we have yet to see it affected by being thrown on the ground.  In this way it serves to protect the relatively fragile alien on the inside.

The two snap fits of our yoyo are both extremely tight.  We were forced to use an arbor press for the ring fit, and we developed a special metal tool to press the alien without harming its antennae.  While this increased assembly time, it made our yoyo exceedingly robust.  We can forcefully throw in on the ground several times before it comes apart.  Also, our design protects our most fragile part inside the other three.

We are very happy with our final product.  Our UFO-yo is attractive, comfortable to use, and durable.  By utilizing 3D machining, we could produce interesting features and parts that help distinguish our yoyo from the norm, and also help hide our weld lines.  The tight snap fits and strong dome make our yoyo exceptionally resilient to wear and impact.  Because of all this, we believe our yoyo is truly out of this world.