Design and Manufacture II: Yo-yos!

No, this isn’t an up and coming yo-yo design Mars (the company that makes M&M’s) is putting out to promote their delicious treats. What you see above was completely designed and manufacture by a team of MIT students, myself being one of them, for course 2.008 (Design and Manufacturing II). 2.008 starts with an introduction of CNC (which stands for Computer Numerically Controlled) machines, or machines that can follow directions and operate automatically to produce important features of the part being made.


So how did we come up with an idea for an M&M yo-yo? Well, to start off the brain-storming session, the course instructors let us take a look at yo-yos made by past students. And so, we took a look through a box of yo-yos that sparkled, lit up, and took various shapes (including one that looked like Sonic the Hedgehog, my personal favorite of course). While looking through the box of toys, we came across a yo-you that was supposed to hold Pez candies and we though “We should make something that holds candies.” Shortly thereafter, I chimed in with “What if we could use the color of the candy to make the yo-yo look cooler?” By that time, we were all excited about the idea of making a colorful yo-yo that could hold your candy. And what better choice than colorful and delicious M&Ms?


The first step toward actually making the little toys was to create the molds. Most plastic parts, especially little things like toys, are made by injection molding, in which melted plastic is shot into a metal mold that has the negative shape of what you are trying to create, hence the “injecting” part. So our team divided up into pairs to make the molds that would eventually produce our yo-yos. Two of the parts are made with thicker colored plastic, and one part (with the M on it) is made of a thinner clear plastic. Each part needed molds to give the plastic shape.

These are the mold pieces I was responsible for, along with my partner Paula Te. The molds here are for the body part of the yo-yo, which makes up the center portion of a typical yo-yo. The curved dish part on the right gives the yo-yo the curved shape, and the big cylinder with the 6 holes on the left mold stamps out the part of the yo-yo that holds the M&Ms. The holes themselves are for the ejector pins, which push the plastic part out when it’s finished being injected.

Once the mold was ready, we had to make a little more than a hundred parts in order to assess the variability of the manufacturing process. That’s right, hundreds of yo-yo parts, shown here strewn across my dorm room floor…

You can also see the different shades we got from switching colors (it takes a while for the different colored plastic to work its way through the machine). If you look carefully, you can also see the little stubs where the plastic shot into the mold, before they were cut off. If you look at plastic things in your own house, you can see evidence of that kind of stuff!

A few brave parts didn’t quite make it through the manufacturing process. The parts graveyard looks something like this…

Poor number 73… Just didn’t have enough plastic…I can’t look!

Sometimes, a little bit of air can’t quite get out of the mold fast enough to make way for plastic, especially when you have a relatively big part like a yo-yo body. When are gets trapped and compressed really hard, it can combust,  causing the burn marks you see here. Ouch!

110 here isn’t quite dead, but might be considered “defected.” As I mentioned earlier, sometimes the colors mix when you switch them in the machine. Don’t worry 110, I still love you!


Just like it sounds like, assembly means putting it all together! Each yo-yo gets a center rod, 2 body pieces, 2 M covers, and 2 retaining rings to hold it all together. Here you can see a pile of yo-yos with there strings on.

And some retaining rings ready to go.

And what do you get? A bunch of awesome yo-yos! But how do they work? Here’s what you do: grab the clear plastic “M”, turn it until the hole in the clear plastic layer lines up with the hole in the retaining ring, and fill it up with M&Ms. Close it by turning the plastic M back, and then your ready to roll! Literally!

Here are a few more pics of the cool yo-yos:


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