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During the summer of 2024, I led four engineering interns at the Segal Summer Internship in building a safe automated swing that supports 110 lbs and works with the assistance of an e-bike motor, a scotch-yoke system, and damping mechanisms to facilitate the use of motion in infant medical treatments. This was a 5-years project at the Segal Design Institute, and I received the leadership for the team responsible for finalizing the mechanical system. We had ten weeks to work on it, and we were oriented by Professors Brown and Gatchel, advisors of the Manufacturing and Design Engineering program at Northwestern University.
The final solution seems simple, which might be one of my biggest lessons from this project. As a product designer, my work is to find intuitive solutions that will prompt users to think, "How I did not think of this before," hiding multiple failed trials and experiments. As the project leader, I also learned that my motivation would inspire my teammates to work harder. Listening to their ideas was also essential, keeping everyone accountable for the steps taken and maintaining everything organized. I was also responsible for bi-weekly design reports and - almost daily - check-ups with our advisors, guaranteeing all improvements were notified and no time was wasted solving challenges that could be easily tackled by asking our more experienced professionals at the design institute.
The video below shows the most successful iteration we achieved. We focused on building a safe mechanism to maintain the swinging motion until the user decided to stop it or whenever an unpredicted accident happened (e.g., someone hit the swing.) This page also presents the challenges and approaches we took during this project.
swingvideo_noaudio.movTHE SCOTCH-YOKE SYSTEM
The system we chose to transform the rotational movement from the e-bike motor to the linear one that hits the bar attached to the swing is called "scotch-yoke." It is composed of a rotational piece, a knob, and a yoke, with a hole that determines the linear movement and horizontal shafts that give it support. As a white-space project, our most significant challenges for this piece were determining measurements and ensuring precision.
Here, we also chose to have an S-shaped curve in the center of the yoke instead of a traditional straight line. The straight line guarantees a linear movement with no change in speed. While we observed how users would pull and push traditional swings, we determined that our system should slow down at the ends as it damps the hitting to the bar. This was a mechanical solution to having a system with different speeds instead of reprogramming the motor.
The acrylic pieces here should be made out of metal for future development. This would allow the swing to work with a higher weight and achieve a more significant swing motion and speed. Our pieces were made of acrylic to facilitate design iterations and reduce costs while testing simply. We also built the system so pieces could be attached in different locations, and we could study where it worked better.
THE DAMPING PUSHERS
Our system was based on the movement someone does while swinging someone else mechanically. When thinking back on this, it is easy to notice how our hands dampen the force coming until an instantaneous stopping, when it is instantly pushed in the other direction. This system was similar to what we could find in springs and dampers. Therefore, we ideated many different mechanisms with these components, built a few different ones, and continued with the most promising one, considering the few weeks we had left in the program: the springs.
They worked well in ensuring the bars would not be hit by a rigid movement of a rigid push and were quickly changed for testing and according to modifications in our structure.
The distance between the two pushers was determined to present an optimal swinging range and allow a mechanical stop while the motor continued. For this safety mechanism, the bar in the middle is not moved by the pushers if stopped, and there is no starting manual push. This way, deactivating the motor instantly is unnecessary if anyone stumbles behind the swing or wants it to stop instantly.
THE MOTOR AND PULLEYS
Another critical element of the swing is the system of pulleys attached to the motor and the programming of this itself. The pulley was used to reduce the engine's speed by half mechanically, and the motor was reprogrammed. Hence, the five different "assist" options are distributed in the best range necessary according to the testing and based on the expectations for how users might use this product. These can be controlled by an intuitive small screen that comes along the e-bike motor.
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