For my senior design project, I worked with a team to develop a variable-pitch propeller system for a quadcopter that used coiled NiTi shape-memory alloy (SMA) to twist the blades and boost takeoff thrust by a targeted 11%. The concept was to retrofit an off-the-shelf drone with a custom propeller hub and SMA actuation system, so pitch could be increased on command without adding bulky servos or linkages.
I helped design and iterate a new propeller hub and bracket with an internal bearing, fishing-line routing channels, and a mechanical stop to limit negative pitch. This replaced the stock hub and significantly reduced the torque required to rotate the blades. I also contributed to deflection testing that mapped propeller pitch angle versus applied load, and to the thrust stand: a load-cell/Arduino/ESC setup with Python post-processing to measure thrust as a function of PWM and to calibrate the SMA force output.
On the electrical side, I assisted team members to implement an SMA drive circuit around an ESP32-C3, high-current transistor, and a 7.2 V NiMH pack. This enabled remote actuation while keeping the system compact enough for flight-scale testing. Despite this, the integrated prototype ultimately failed: transmitting SMA force through fishing line routed inside the spinning motor shaft caused tangling and line failure at speed, preventing us from collecting reliable variable-pitch thrust data.
Although the system did not meet its performance goals, the project forced us to work end-to-end: project budgeting, CAD and rapid prototyping, experimental design, embedded electronics, and post-test failure analysis. Despite the project's setbacks, the idea behind SMA actuation in small drone designs is still feasible with potential weight savings benefits.
The project notebook can be downloaded below.
