Fall 2025 24-370: Mechanical Design: Methods and Applications

Final product made in partnership with Chloe Trujillo, Cordelia Pride, Miranda Trujillo, Katherene Qi, and Julia Song

As part of my Mechanical Design: Methods and Applications course, I, along with five other students on a team, was tasked with designing and manufacturing a prototype of an assistive device. We chose to design assistive kitchen tongs because they are commonly used but present challenging grip ergonomics and wrist stress during use.
​
Before designing our product, we surveyed our target customer group to determine their priorities for an enhanced pair of kitchen tongs. From our survey, we determined that older adults with wrist mobility issues prefer kitchen tongs that allow a full range of motion (180-degree rotation and easy grasping of objects) without requiring significant wrist motion or strain. They also preferred tongs with more comfortable grips.
​
Based on our survey, we designed kitchen tongs controlled by button presses, with the thumb positioned on top of a vertical handle for comfortable gripping and easy holding. These buttons would correspond to four actions: open, close, turn clockwise, and turn counterclockwise. The tong arms would be inserted into slots on the front of the mechanism and removed via buckle-like clip ends for washing. The tong arms would rotate via two servos, housed in a protective casing that also contains the gears required for actuation.
​
Based on this design concept, we used pre-made stainless steel tongs as the tong arm ends and cut them off to attach to our buckles, which we 3D printed from PETG. The servos we used were Dynamixel and were capable of providing sufficient force for grasping and rotating, based on our calculations. The gear mechanics for opening and closing the tong arms would be controlled by a 2:1 simple gear train from the motor and two 1:1 gears interfaced directly, enabling the tong arms to actuate in opposite directions with equal magnitude. These would be housed within an internal sun gear, which would then be rotated by three planet gears on a simple controller, using the same type of Dynamixel servo at the back of the housing. This would allow the central arms to rotate without requiring a large force from the servo itself. The housing would be attached to a hollow handle that allows the wiring from the four buttons on top of the handle to pass through it and into the housing, which would be controlled by a microcontroller and powered by simple battery packs. The housing, gear system, and handle would all be 3D-printed in PETG, with the handle cushioned using replacement bike handle material. Due to the weight of this mechanism, we also designed and installed an acrylic arm brace attached to the bottom of the housing to enable stronger control of the product by using the shoulder and elbow rather than the wrist.
​
The final mechanism required numerous iterations to achieve assembly tolerances, gear grease to ensure proper rotation with minimal resistance, and soldering and circuit mounting to ensure adequate housing of the internal mechanism. Ultimately, we were able to successfully grab and rotate a grape 180 degrees clockwise and counterclockwise. This project helped me and my team recognize the importance of proper planning for assemblies and complex designs, as well as the importance of accountability, dividing work, and communicating challenges and expertise.​