A portable upper arm exercise machine offering easy to use, variable workouts.

Class/Organization: ME 691 Advanced Product Design and Engineering — Boston University

Role: Team Leader

Duration: Aug 2021 - Dec 2021

Problem Statement: How can we turn a hand crank into an exercise machine that appeals to a specific market?

OUR SOLUTION.

We designed the Rotoflex: an upper arm exercise machine designed for at-home workouts for those who are looking to get more active, but do not have the space or resources for a full at-home gym. Over the course of the semester, we researched possible markets and customers, developed our own list of product requirements, modeled the full design in CAD, and built a high-fidelity, functional prototype of the product. As the team lead, I oversaw the timeline and documentation of the project, while also leading meetings and discussions regarding critical design decisions.

MARKET, CUSTOMERS, AND PRODUCT REQUIREMENTS.

According to the ACSM Health and Fitness Journal, COVID-19 has had a huge impact on fitness trends and the market for at home exercise. As online training and personal exercise equipment become more popular, our goal was to bring new workout equipment for the upper body inspired by cycling to those exercising outside the gym.

To help us in this goal, my team sent out a survey to identify how often people work out, how they prefer to work out, and what features they would like to see in exercise equipment. From our results, we determined that our product is geared towards people who exercise frequently (3-5 days a week) as well as those who exercise less frequently (0-2 days per week) but are looking to exercise more. From the survey results, the majority of customers preferred a cheap, portable and easy to store option for their exercise equipment.

Our product aimed to add variety and options to upper body workouts, specifically through targeted strength training and cardio as our data found these two focus areas had the most interest. We also found a larger majority valuing portability and affordability, two elements that fit a personal item.  Going off this data and the global climate with COVID-19, our group has decided to focus on a portable and affordable machine that will give our customers the ability to workout wherever they want. This machine will aim for a price point around $100 which was deemed the most desired price point by our survey. From this survey and market research, we were able to identify the following product requirements, listed in order of priority.

PROCESS.

i. Conceptualization
Initially, my team struggled with thinking of initial concepts that were very similar to competitor products such as an upper body ergometer, but we were encouraged to really think outside the box while keeping our solution simple. In our first few ideas that were similar to competitor products, we found that the features we could add to make our product stand out would make it far exceed our price point of $100. After some further team meetings further brainstorming of new ideas, we finally decided on creating a clamping table crank. We were drawn to the table crank because it offered the unique ability of being modular, usable in multiple orientations, and easy to use with different handles.

ii. Prototyping the Resistance Mechanism
After deciding on the overall product concept, we had to decide on the resistance mechanism that would be used in the table crank. We drew from some previous product ideas such as using resistance bands, but ultimately decided on using some form of a brake pad and linear actuator to create resistance. This was because of our price limitation of $100, where we could easily purchase resistance felt and replace it for the source of resistance, especially in comparison to bands or magnets.

Ultimately, we used a bolt as a shaft with a threaded end. This would give a direct and easy adjustment of the compression of the system using a friction pad disk and high strength spring to provide force to push the friction pads against the cranking flywheel. This would allow the user to easily tighten or loosen the main nut in order to control the resistance and also allows for modularity in areas like friction disk type, spring strengths and different handles while offering easy maintenance and replaceability of those parts. In our initial prototype, we used purchased parts for the bolt, spring, and bearing, and 3D printed the flywheel, adjustment handle, and friction disk.

After confirming the functionality of our resistance mechanism using friction pads, a spring, and flywheel, our focus turned to finetuning the usability of our product and the resistance mechanism. To do so, we machined our aluminum flywheel on a mill and 3D printed two handles and the product housing case.

PRODUCT.

At the end of the semester, we were able to deliver not just the resistance mechanism for our product, but also a high-fidelity prototype of the entire product for our professor and peers to test in the different orientations and resistance levels. As a group, we also decided on the name, Rotoflex for our product. The Rotoflex had the following features:

• Two different orientations for use

• Adjustable resistance linearly from 2 lbf to to 18 lbf

• Easily replaceable parts

• Square enclosure with side handles for easy carrying and storage