09.3 Design Process
Background
Tong has a cat that is particularly amused by hair ties and objects held in front of its face. However, Tong does not always have time to actively play with the cat, which can lead to boredom or feelings of neglect. To address this problem, we set out to design a cat-toy mechanism that could entertain the cat independently whenever it feels bored. The goal was to create an engaging, interactive device that mimics the motions of human play while operating autonomously.
Brainstorming
During the initial brainstorming phase, we identified several key requirements for the design. The mechanism needed to hold a toy in multiple orientations, primarily up-and-down motion (flicking), and also be mobile to maintain the cat’s engagement. We proposed an arm-like mechanism that could mimic human hand movements when playing with a cat, mounted on a small car to allow linear movement.
To achieve smooth and controlled motion, we decided to use servo motors to actuate the arm’s links and bearings at the joints to reduce friction. We also explored additional interactive motions, such as a throwing and reeling action where the arm could release a toy attached to a string and then pull it back in. A rotatable base was considered to increase the range of motion, allowing the arm to rotate independently while the car moved.
We also discussed incorporating legs to raise the car, since cats are capable of jumping relatively high. Additionally, we considered using springs in the links to provide a default resting position for the arm when the mechanism was powered off.
Prototyping
Tong began creating a CAD model in SolidWorks based on our initial sketches. During motion simulations, several parts interfered with one another, prompting each team member to suggest and implement design edits. We eventually arrived at an initial prototype that functioned well in simulation.
However, when preparing to 3D print the links, we discovered that each part would require approximately nine hours to print. Due to TIW time constraints, this was not feasible. We explored scaling down the model to reduce print time, but doing so prevented us from using the bearings we had already obtained, as they no longer fit the resized parts.
As an alternative, we created simplified components that demonstrated the intended motion. Instead of custom-designed links, we used shafts and couplers to represent the arm’s movement and validate the mechanical concept.
Experiment
To reduce 3D printing time, we removed excess material from the links and redesigned the car body. Cavities were cut into the underside of the car to significantly decrease print time while still maintaining enough structural support for the electrical components.
During assembly and testing, we observed that the gears slipped on the shafts, which compromised motion reliability. To address this, we superglued the gears onto the shafts. We also replaced the servo motor used for the bottom gear with a compact brushed motor, as the servo did not provide sufficient torque to rotate the gear system under the weight of the full mechanism and bearings.
Additionally, we adjusted the gear train by adding another gear. The original gear ratio limited rotation to approximately 180 degrees, but the updated configuration allowed for a full 360-degree rotation.
Another issue arose with the servo motors controlling the lower arm link, where the connecting parts began slipping after repeated trials. We resolved this by taking advantage of the threaded interior of the servo motors. Screws were added through the connecting parts and into the servo, eliminating slippage and improving the mechanical connection between the motor, link, and coupling.
Conclusion
Because of the large size of the components, we attempted to resolve as many potential issues as possible in the SolidWorks CAD model before assembling the final project. While this allowed us to eliminate several interferences, additional design challenges emerged during physical assembly after printing. These issues required us to return to the brainstorming phase, where we iteratively developed, tested, and refined solutions. This cycle of problem identification and redesign ultimately led to improvements that better suited the overall mechanism.