Thursday, April 17, 2014

Body IM Update

We finished our optimization. Here is the result of the final setup:

Unit (in) Outer Diameter Inner Diameter Thickness (injection side) Thickness (Weld side) Height

O.1 2.508 2.38 0.063 0.063 0.684
O.2 2.507 2.384 0.061 0.064 0.688
O.3 2.509 2.384 0.062 0.064 0.687
O.4 2.509 2.385 0.061 0.066 0.689
O.5 2.509 2.381 0.063 0.063 0.686
O.6 2.51 2.382 0.061 0.065 0.69
O.7 2.507 2.383 0.062 0.065 0.688
O.8 2.507 2.379 0.062 0.064 0.689
O.9 2.51 2.385 0.06 0.064 0.688
O.10 2.508 2.38 0.062 0.066 0.686
Average 2.5084 2.3823 0.0617 0.0644 0.6875
Std 0.00117379 0.00221359 0.000948683 0.00107497 0.00177951

Comment: OD and ID are slightly bigger than the design. The thickness is fairly uniform everywhere. Since the face IM team increased the face diameter, they fit really well together.

Updated Gantt Chart:

Thursday, April 3, 2014

Body IM Test Run and Updated Gantt Chart

The Body IM team (Javier & Xiaoyue) did a test run of the body injection molding. The body turned out well (see pictures below). The shims and nuts were successfully embedded in the plastic, and there were few flashes. We will do the optimization of injection setup next week.

Pic 1: Results of test run.

Pic 2: Nuts embedded in the body.

Pic 3: IM part before cutting out the runner.

Pic 4: Javier in the shop =)
Also, here is an updated Gantt Chart of the Body IM team. 

Wednesday, April 2, 2014

Circuit Testing

Here's a video of the circuit in action. It consists of two ball tilt switches, four LEDs, and a 3V coin cell battery. The circuit is taped to the outside of a yo-yo to simulate proper spinning conditions.

Thursday, March 13, 2014


Initial Circuit Design and Part Orders

Our goal is to have our yo-yo light up when it spins. After looking at previous LED backlit Yo-Yo designs we settled on the Roller-Ball Tilt Switch as our mechanism for turning our circuit on only (in theory) when the Yo-Yo spins. There is a conductive metal ball inside of the switch’s cylinder that will short the leads, completing the circuit, when it rolls to the bottom of the cylinder. If we orient the switch with its contacts pointed radially outward the ball will short the leads when forced outward while the yo-yo is spinning. With only one switch this is not of very much benefit to us; whenever the yo-yo is held with the switch below the central horizontal axis the yo-yo will light. This is unfavorable because the yo-yo would have to be stored carefully to avoid draining the battery. If, however, we put two of these switches in series and opposite each other, both pointed radially outward, only one ball will be able to contact at a time unless the yo-yo is spinning.

Above: Circuit diagram. The circles are our 5mm LEDs, the central red circle is a coin cell battery, the two rectangle are our switches (in series between the battery’s ground and the LED ground ring), and the grey outlines are the inner diameter of our yo-yo and, inside of that, our circuit boundary).

We have developed a circuit for testing and ordered the parts to do so. Below is a basic schematic (for the purpose of calculating necessary voltage sources and current-limiting resistors).

I have ordered an assortment of 5mm Super Bright Water Clear LEDs- the bulk price was fairly good (300 LEDs for $13), and the assortment of colors will satisfy all members of our team (the one thing we could not agree on was a single color; we could, however agree that multiple colors [a single color per yo-yo] would be awesome). The circuit will be essentially the same for all colors, although the voltage drops are split into two different ranges depending on color, so we will have two different resistor values for optimal brightness.

Forward Voltage (V)
Purple (UV)

Above: Forward voltages for various colors of LEDs. For the purposes of resistor calculations I split them into two forward voltage categories: 2.2V and 3.2V.

The recommended current is 20mA. The voltage source is made up of 3V coin cell batteries. We will likely need two per yo-yo for the 3.2V LEDs (and may just go ahead and use the same for both for continuity). Using Ohm’s Law, R=V/I, I found that the resistors should be 30Ω for a 3V source and 2.2V drop, 190 Ω for a 6V source and 2.2V drop, and 140 Ω for a 6V source and 3.2V drop. I ordered 200 Ω resistors for testing purposes, as 190 Ω is an unusual resistor value. Additionally, we will need 200 Ball Tilt Switches (two for each of our 100 circuits). I ordered 230 to account for errors on our end and switches that arrive broken. Everything is scheduled to arrive over Spring Break which will give us time to test and optimize our circuit.


Cost ($)
22 AWG Solid Wire (Hook Up Wire)
25 feet
CR2032 Lithium 3V Batteries
50 batteries
LED Assortment Kit
300 LEDs
20 each R,Y,G,B,W,UV
Ball Angle Tilt Vibration Switch (SW-520D)
230 switches
Resistors (200Ω)


What still needs to be ordered/tracked down: solder, copper braid, and violet LEDs (the LEDs can wait until we get our initial circuit working).