Senior project spotlight: Charlie Biggs

Engineering Design Projects (ES 100), the capstone course at the Harvard John A. Paulson School of Engineering and Applied Sciences, challenges seniors to engineer a creative solution to a real-world problem.

Mechanical Battery for HPT (Human Powered Transport)

Charlie Biggs, S.B. ’21, mechanical engineering

Please give a brief summary of your project.

This project was centered around designing an efficient, competitive, and reliable means of energy storage in a mechanical battery that was made entirely out of recyclable or environmentally friendly materials. This was to be applied to the category of light transport (including human powered transport). The final solution was a flywheel sealed in a vacuum connected to a driven pulley by a continuously variable transmission controlled in part by the flywheel's rotation speed and in part by the user.

What was the inspiration for this project?

Electrochemical batteries are currently one of the greatest limitations on electric vehicles (EVs) because the production of those batteries emits tens of tons of CO2. Because of this, if the lifetime of the vehicle includes the mining of its materials and manufacture of its components, EVs are just as environmentally damaging as internal combustion engine vehicles are.

Personal EVs are becoming more and more frequent, however, and this means more and more electrochemical batteries are being produced.

How will this project help solve the problem you identified?

This project circumvents that issue by using more commonly available and recyclable materials. No lithium or other harmful resources are required to produce one of these, and it is capable of storing enough energy to cover both legs of most bicycle commutes.

What were the biggest challenges of this project?

One of the greatest challenges was determining a solution that minimized the losses in the flywheel. The ultimate design involves a vacuum and magnetic bearings to store the flywheel in a near-frictionless space. Its axle is magnetically coupled through the wall of the vacuum-sealed housing in order to transfer power to the transmission. There were many days during the design of the final iteration that I was convinced it was impossible, and I am very glad I was able to find a solution.

Next was determining a way to remove energy from the flywheel without using motors and generators which would cause enormous losses. The mechanical transmission I designed is far more efficient than a motor-generator pair since it does not convert the energy to electrical energy and then back to kinetic energy. 

Last was the implementation of finite element analysis on the key parts to determine which materials would be light enough to reduce the weight and strong enough to ensure the user's safety. This involved running hundreds of simulations—many of which failed and many more of which yielded surprising results.

What did you learn through this experience?

I learned a lot about scripting for Abaqus (the finite element analysis software I used) in Python and about learning to adapt and work around obstacles and limitations found along the way. The vacuum, for instance, would not be possible without the magnetic coupling, and the flywheel’s ultimate energy capacity would not be possible without the vacuum or the magnetic bearings.