Picture This

Major moves were made this past week! We started narrowing down our potential features and started to finalize our design. The new model features colored stripes in the top left corner, pegs on the body for the snap rings, no button, and a slot that will hold a small picture. When modifying our final product, we encountered many problems that would arise from the manufacturing process. Some of the factors we had to consider included shrinkage, cooling time, undercuts, binding to the mold, and performance. After taking all of these into account, these were our final components with the processes that accompanied them:

Injection Molding	Camera Body: cylindrical piece; uniform thickness; 10 pegs for the components of the camera front to snap into	Snap fits with front components
	Camera Front Top: cylindrical piece; not a complete circle; only 140.4 degrees; hole in the center of the outer diameter for the lens; extruded face with rounded edges and a filet for the front face of the polaroid; square hole in the top right corner (when looking at a front view) to allow for the camera shutter	Snap fit onto body with pegs
	Camera Front Bottom: Cylindrical piece; not a complete circle, only 219.6 degrees; hole in the center of the outer diameter for the lens; extruded face with rounded edges and a filet to illustrate the front face of the polaroid; outer snap ring; holes on the snap ring for the camera body pegs to slide into
Thermoforming	Lens and stripes: mostly clear, thin thermoformed piece with printed colored stripes on extruded block in the upper left corner; fits between camera front and body	Constrained between camera front and body
	Polaroid Picture: rectangular, white framed thermoformed piece with printed picture (TBD); slides in and out of slot in body	Slides freely in and out of slot in body, held in place with friction from small pegs

Exploded view of Yolaroid

Accompanying the final features were the final dimensions with tolerances:

		Target Numerical Value (inches)	Expected Tolerances (inches)
Diameter of Yoyo Body		2.5	+/- 0.005
Max Height of Yoyo Body		0.425	+/- 0.005
Max Length of Top Camera Front		0.75	+/- 0.005
Max Height of Top Camera Front		0.65	+/- 0.005
Max Length of Gap for Thermoformed Stripes		0.476	+/- 0.005
Max Width of Gap for Thermoformed Stripes		0.30	+/- 0.005
Max Length of Shutter Gap		0.229	+/- 0.005
Max Width of Shutter Gap		0.30	+/- 0.005
Max Width of Bottom Camera Front		2.5	+/- 0.005
Max Length of Bottom Camera Front		1.670	+/- 0.005
Max Height of Bottom Camera Front		0.650	+/- 0.005
Max Slot Thickness		0.125	+/- 0.01
Max Slot Height		0.7	+/- 0.01
Max Length of Stripe Block		0.476	+/- 0.005
Max Width of Stripe Block		0.30	+/- 0.005
Max Height of Stripe Block		0.40	+/- 0.005
Max Height of Thermoformed Piece		0.53	+/- 0.005
Outer Diameter of Thermoformed Piece		2.30	+/- 0.005
Outer Diameter of Lens		0.98	+/- 0.005
Height of Lens		0.5	+/- 0.005

One of the biggest challenges was making sure the product was feasible through the injection molding process. At first, we planned on using pegs protruding from the underside of the top snap ring and slots cut into the underside of the bottom snap ring. However, we soon realized that this would lead to very unideal undercuts and brainstormed a 3 potential solutions including pegs on the outer ring, overmolding, and a design featuring a grabbing mechanism between the top and bottom piece. As a team, we concluded that overmolding would be a bit time consuming for our team of 4 and the grabbing mechanism would be unnecessarily complicated. We decided on continuing with using pegs however instead of on the underside of part of the snap ring, a ring of pegs on the body will easily allow the top snap ring pieces to attach to the body. We hope this will reduce complication in the manufacturing and assembly of the mold while also yielding a strong fit!

Assembly Plan for Yolaroid

In addition to deciding that the ring of pegs on the body would be the easiest and hopefully foolproof method, we decided that we would love to put more work into including our polaroid picture mechanism! This would be a special feature on our yo-yos that would make a picture pop out when a button is pressed. After very length discussions to design a method for this as well as research on similar mechanisms (like SD card slots), we decided to design the slot and polaroid piece to be modeled after press fit caps as seen on chapsticks and small tubes.

Polaroid picture snap fits into side slot of Yolaroid

Since the top and bottom snap ring pieces were now going to snap onto the body by using a ring of pegs, we had to figure out our snap fit interference tolerances. We specifically looked at one of the past yo-yo's, the hamster wheel yo-yo, which similarly had a ring of pegs to attach the dome onto the body. Using this yo-yo as a guideline, we decided that our yolaroid will have a snap fit length of engagement of 0.150" and snap fit tolerances of about 0.006" diameter interference. We hope that these tolerances will allow the front pieces to easily and pleasingly snap onto the body.

To further assist optimization of our injection molded parts, we made sure the parts had a relatively uniform thickness and were as thin as possible to reduce cooling time. As a result, we decided the maximum thickness of the top and bottom snap ring to be 0.243" with thinner fins to prevent deformations caused by uneven cooling, as well as a maximum thickness of the body to be 0.221".

Accommodating our mold to potential shrinkages is especially important in our design to make sure the camera front and bottom pieces snap into the body. In order to come up with our shrinkage compensation plan for our yolaroid, we looked at past yo-yos that were similar to ours in size, features, and other details. To compensate the average shrinkage of similar yo-yos of 1.47% concluded from our background research, we have decided to scale the mold by 1.0147. To assist with making the injection molded pieces easier to take out of the mold, we also added a draft of 5 degrees.


Below is a summary of the design features for each injection molded part:

Injection Molded Part	Design Features
Body	-Uniform thickness; thin fins -Draft angle of 5° on surfaces shrinking onto a boss -Slot cut out at the parting line -Bumps on the ring to act as a lock mechanism
Top Snap Ring	-Uniform thickness -Thin fins -Draft angle of 5° on surfaces shrinking onto a boss -Holes on the ring for pegs
Bottom Snap Ring	-Uniform thickness -Thin fins -Draft angle of 5° on surfaces shrinking onto a boss -Holes on the ring for pegs -Slot cut out at the parting line

We believe that the yo-yo performance is dependent on the weight distribution of the yo-yo and will need to take in account the potential imbalance due to our slot and polaroid picture piece. We also acknowledge that parts of our design are subject to change such as tolerances, physical appearance, and our polaroid picture mechanism. We plan on establishing more specifications on the tolerances and secure/release mechanism for the polaroid picture once we have a better understanding of these challenges. We will evaluate our final yo-yo based on how well it meets our target specifications by using calipers to measure the distances that we selected and creating a graph of where these values fall relative to our nominal value. This data processing will help us see how accurate our process was and to understand future deviations that we find in performance!

Using our more in depth design for manufacturing plan for all of our yolaroid pieces, we are ready to start molding all our pieces! Let's get molding!