Smart Yo-yo

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Figure 1: Smart Yo-yo



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

How It Works

The concept behind the smart yo-yo is a brake that engages when 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 attached to the string.

At low speeds the spring force is stronger than the centripetal force acting on the weight, and the brake is engaged so the yo-yo cannot spin freely. 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."

This method is much more consistent as opposed to traditional yo-yos that do not have multiple parts. 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 in 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.

The dimensions of all the parts were found which allowed the analysis of the system using dynamics. 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.


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 allows spinning in the main bearing Steel
5 Spring Input Keeps brake engaged Steel

View Yo-yo in Motion