13.3 Initial Prototype

Iterations

The initial CAD build demonstrates the fundamental layout of the components needed to achieve the rotational motion of the egg, along with the base four-bar linkage system. A central track meshes with two gears to ensure synchronized rotation. These gears include an extruded face, which increases their effective range of motion. Egg holders are mounted on this extruded face, designed to securely cradle an egg between them during operation. Not shown in the current view is the crank-slider mechanism located behind the main baseplate, which provides the necessary linear input to drive the track.

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Figure 1: Front view of the Initial CAD

The part shown in Figure 2 is a modified face that combines Link 2 from the four-bar mechanism and integrates an arm that holds the blade used to crack the egg. A slot cut into this face is designed to guide and hold the egg steady, positioning it directly above the blade to ensure a clean and consistent crack. This slot will align with the egg holder during operation to minimize lateral movement.

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Figure 2: Front face iteration 1

One of the most important interactions highlighted in figure 3 is the flat face extending from the track. This face comes into contact with a matching flat surface on the gear’s extruded feature. When these flat faces meet, the track moves linearly while the gear and egg holder remain temporarily stationary. This brief pause in the rotational motion is essential for cracking the egg precisely onto the blade.

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Figure 3: Rearview of the Prototype depicting the flat face facilitating intermittent motion

As the crank-slider drives the track forward, an extruded section on the track functions as a lever arm to push the egg downward. The flat face clears the pivot point of the gear just as the track and gear teeth engage again, allowing the egg holder to resume its rotation and complete the motion cycle. This carefully timed interaction enables both the cracking and separation phases of the mechanism to occur with consistency and control.

Prototype

For prototyping purposes, we simplified the mechanism’s geometry by leveraging symmetry. Instead of modeling the full slider-crank system, we replaced it with a manually operable tab-and-slot setup to streamline development. This approach made it easier to iterate on the mechanism’s motion without actuation. The egg holder for this prototype will be 3D printed using PLA due to material availability; however, the final design will utilize TPU for its flexibility and durability.

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Figure 4: Left half of Egg Cracker Mechanism in the initial state with a plastic egg to mimic a real egg.

A major aspect of the mechanism is the use of intermittent motion. This ensures that the egg remains steady while force is applied to crack it, reducing the chance of premature or uncontrolled breakage. The timing of this intermittent motion is determined by the geometry of the track and the length of the flat face on the cam profile. These features work together to pause the system briefly during critical operations, enabling a smooth and controlled cracking process.

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Figure 5: Left half of the Egg Cracker Mechanism depicting the egg getting pushed into the blade.

The prototype design intentionally leaves out some non-critical elements to focus on the mechanism’s core functionality. To keep things simple, the model uses bearing-less joints and only represents one side of the symmetric egg-cracking system. We excluded the base support for now, so the prototype won’t stand upright on its own. Instead, this version emphasizes the key movements needed to crack and separate the egg effectively.

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Figure 6: Left half of the Egg Cracker Mechanism depicting the end of the rotation and the Four-Bar Linkage positioned to push the eggshell out.

Throughout the project, we worked through several iterations, each refining both the functionality and form of the egg-cracking mechanism. Our primary goals for the final system are as follows: (1) push the egg downward into a blade to initiate the cracking process, (2) split the egg into two halves to allow the yolk and whites to drop cleanly into a bowl, and (3) rotate each half of the eggshell so the cracked faces become parallel to the ground. As a final step, the four-bar linkage will continue its motion to eject the empty eggshell halves from the holder.

Bill of Materials

The prototype we have currently has 2 acrylic sheets: one which contains the vertical slot and the other which pushes the egg down onto the blade. The pushing mechanism is made of PETG, but we may change the geometry so that it pushes the egg onto the blade before the mechanism rotates around. The blade is currently made of PETG for the prototype, but we plan on using either Aluminum or Stainless Steel Razor Blades for the final prototype.

The acrylic slider block has a toothed side which interfaces with an acrylic half-gear (this setup functions as a rack-and-pinion). When the slider block moves downward, it turns the gear clockwise. The gear shares the same shaft with a PETG connecting link, which has the egg holder piece. For the prototype, the egg-holder piece is made of PETG, but for the final project, it will be made with TPU. Finally, the PETG connecting link is connected to a final link with a spacer that pushes the egg outward after it has cracked and the contents have been extracted. 

We plan on bringing in 220 Ohm resistors and a 12VDC Power Supply for the electronics. The 220 Ohm resistors will be used for the button circuits that connect directly to the Arduino. The button circuit will be used to turn on and actuate the motion. The 12VDC Power Supply will be used to power the driver and stepper motor that will be used to move the slider mechanism downward.