THE AUTOMATIC CONTINUOUSly VARIABLE TRANSMISSION BICYCLE
Best Overall Project at The 2024 Fall Design Expo
Design
The CVT allows for theoretically infinite gear ratios and prevents the user from needing to change gears, improving the overall user experience. The system will enable inclination and speed based automatic gear selection through a large 450% gear ratio range.
The Electronics and Sensing
I was Electronic and Control Systems Lead for this project. The sensing system consists of an ESP32-based microcontroller with WIFI/Bluetooth, a 6-DOF IMU, and an incremental encoder. Users select an ideal pedaling effort in automatic mode or directly select gear ratios in manual mode via this display and potentiometer on the handle bars. Then, a PID controlled DC motor actuates gear ratio changes. In automatic mode, the PID set point is dependent on an outer proportional control loop that uses inclination data from the IMU (Kalman filtered) and speed from the incremental encoder on the CVT input shaft to converge on the desired pedal effort set by the user.
The CVT
This dual cone CVT features 3D printed cones/mounts, limit switches, a custom tensioning rod, custom sprockets, custom shaft collars, and a machined aluminum housing. A teflon rod, high speed lead-screw and ball bearing carriage enable smooth transitions between gear ratios.