Blog Deliverable 1: Initial Yo-Yo Design + Semester Plan

Description of Initial Yoyo Design:

Our yo-yo consists of 4 distinct injection-molded parts and 1 thermoformed part. Below, we discuss how each part will be manufactured and assembled, and any considerations that we made for manufacturing. The Solidworks model of our initial yo-yo design is shown here: 

Injection Molded Parts:

1. Hamster: The hamster will be injection-molded in a multi-cavity mold. The back of the hamster has a press-fit attachment that fits with the connector piece. We tried to make the hamster small enough that it could be made in a multi-cavity mold, because this will speed up our manufacturing process.

2. Connector piece: The connector piece will also be injection-molded in a multi-cavity mold, out of the same color plastic as the body pieces. The connector piece has a hole that press-fits with the hamster, and a peg that will be press-fit into the ball-bearing in the center of the yo-yo.

3. Outer wheel: The outer wheel has a ring and pegs which form the outside part of the hamster wheel. This piece will be injection-molded. The pegs will press-fit into matching holes on the centerpiece.

4. Centerpiece: The centerpiece will be injection molded. This piece contains holes around the rim (into which the pegs will be press-fit) and a hole in the center for the bearing (also a press-fit around the OD of the bearing). The centerpiece also contains a hole in the center on the opposite side for the shoulder bolt/nut. The inside of the centerpiece has been hollowed out to allow for shrinkage (if it were solid, there would be too much material there and shrinkage would be very significant). The centerpiece also contains a ridge that holds the base of the thermoformed piece; when designing this ridge, we made sure to think about the minimum dimensions for tooling (i.e. cutting out the mold on the lathe) and sized our piece accordingly.

Thermoformed part: We will thermoform a clear plastic “shell” which will sit just inside the wheel pegs and rest in a ridge on the centerpiece. The purpose of this shell is to add a bit of support to the outer wheel piece, to shield the hamster & connector piece, and to help us gain experience in thermoforming. The thermoformed piece looks similar to a dome, with straight sides. 

Additional parts: The bearing in the middle of each side of the yo-yo (used to allow the hamster/connector piece assembly to rotate freely with respect to the yo-yo body) will be purchased from an outside vendor.

Table of Specifications:

Spec	Value	Tolerance	How to measure
Mass	.034 kg		Scale
Diameter	2.5 inches	All dimensions should be within +/- .005	Calipers
String Gap	.075 inches		Calipers
Moment of Inertia	2.72*10-5 kg*m2
Maximum Rotational Speed	8200 rpm
Snap fit tolerance		+.003 for OD, -.003 for ID'	Micrometer

We have also created a Gantt Chart, to track our progress and help us plan for the semester. The Gantt Chart can be viewed here.