# Smart Yo-yo

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Figure 1: Smart Yo-yo

## Description

The smart yo-yo is a yo-yo that makes it very easy to return compared to traditional yo-yos.

## How It Works

The concept behind the smart yo-yo is a brake that is disengaged as long as the yo-yo is spinning fast enough. A lever is attached to the hub of the yo-yo and is allowed to pivot from one end. A small metal weight is attached to the other end. In the middle of the lever is a spring which pushes the lever into contact with the bearing. This bearing rides on the center axle and is the mounting point for the string.

At low speeds the spring force is stronger than the centripetal force acting on the weight, and the brake is engaged. This stops the rotation of the bearing with respect to the outer shell causing the yo-yo to wind up. Once the yo-yo is spinning fast enough the centripetal force of the weight overcomes the spring force and the lever moves away from the bearing, allowing the hub to spin freely so the yo-yo "sleeps." Additionally the mechanical break creates an automatic return condition where very little force is required to return the yo-yo.

In traditional yo-yos, the whole body of the yo-yo is one part and has a string wrapped around the middle. It "sleeps" by spinning on the string. Since this depends on many varying characteristics of the string, including how much friction is involved or how tight the string is tied, it is very unpredictable. However with the bearing this modle allows for longer and more reliable spin and sleep times.

Computer models were created of each of the following parts. Using the current model as a guide and accepted values for the material properties. The system was analyzed using the Adams and Ansys software packages and dynamics (hand calculations). The spring constant was found by measuring the deflection after the application of a force in compression on the spring. The centripetal force is dependent upon the angular velocity of the yo-yo; using force analysis of the weight and the spring the angular velocity of the yo-yo needed to disengage the brake was found.

The stresses resulting from these forces on the lever were analyzed using ANSYS. The stresses cause bending and axial tension, both of which are a concern because either can cause failure.

## Parts

The table belows lists the Bill of Materials for the Smart Yo-yo:

Table 3.1: Smart Yo-yo Bill of Materials
Part # Part Name Category # Function Material Picture
1 Hub Support element Houses internal components Plastic
2 Lever Transmission Applies friction to main bearing Plastic
3 Main Bearing Support Element Allows hub and axle to rotate, attaches hub to string Plastic
4 Axle Support Element Connects the two halves of the hub and rotates in the main bearing Steel
5 Spring Input Keeps brake engaged Steel