Design Process - Group 14

Initial Drawings and Ideas

The original drafts for the cat toy explored ideas on how we wanted to approach the mechanism’s function. We wanted the toy to have random movements to keep the cat entertained, while at the same time avoiding scaring the cat.

Project Proposal

Our first ideas were too focused on generating random movements through the use of programming. After meeting with the TA and reviewing some new ideas, we decided to power a four-bar rocking mechanism with a motor, and have it roll over a cam system to create unique vertical movements.

This plan allows for 2 degrees of freedom using the constant rotation of the motor as the only input. While the mechanism will inevitably begin to repeat itself given enough time, the amount of freedom using a cam system gives in designing a pattern for the toy suppresses this issue into insignificance.

First Prototype

The process for creating the prototype was very simple. We repurposed the links for the slider-crank mechanism created earlier in the semester by changing their lengths. We then laser cut the links and fashioned them into the crank-rocker. Then, the vertical path cam and temporary cat wand were cut out. The cam was attached to a base with the crank-rocker and the cat wand was attached with a hinge to the output link.

There were also plans to create a third degree of freedom by using a four-bar slider mechanism to push the cat toy in and out, adding more variation to the movement of the toy after the prototype is created. These plans did not come to fruition, however, due to not investing enough time into planning out and implementing the extra four-bar mechanism.

Final Design

After construction of the final design began, there were not too many major deviations in the plan. We chose to build the project out of acrylic for aesthetic purposes. An actual hinge was used to connect the cat toy to the rocker, and spacers were laser cut and placed between the joints of the links to make sure the links did not collide and get stuck on any loose metal and screws sticking out.

The base plate was designed with regard for the components that we would eventually add later. This was done by placing holes for the rotating link and the motor it's attached to, the rocker, and the electrical components. However, we later learned the given setup would cause the rotator to collide with the electrical components. To remedy this and provide room for the motor, we placed the base plate on legs and placed the electrical components on the lower plate. A miniature table was built to secure the motor and prevent it from spinning.

The final major deviation in plan came with the cam system. We realized our original prototype for the cam bumps were both too close to the rocking link and too steep, preventing the rocker from moving and stalling the motor. This was resolved by creating and placing a cam wall along the edge of the platform for the cat toy to run over. By making the cam bumps larger and further away, this reduced the torque placed on the rocker and provided more room to design patterns for the cam.

While our original plans involved using mechanical components to rotate the cam system in order to provide more variation in the vertical motion of the cat toy, the speed the toy traveled over the cam wall with caused it to leap off the cam quite frequently and chaotically. This was considered satisfactory for our project as it provided the variation we were seeking in our original designs. Finally, an Arduino was used to program more variation into how the motor was run. More details on the programming is in the implementation section.