Problem

Changing gears on downtube-shifting bikes leaves your hands and body in a dangerous position away from the handlebars and brakes. They can also be quite difficult to pull down, and require precise movement to prevent accidentally switching out of multiple gears. This poses a large risk of injury for new bikers or elderly people.

To address this issue, we developed an automatic bike gear shifter that adjusts the gear according to the rpm of the pedal.

Function

We detect RPM with an ultrasonic sensor positioned at the base of the pedal. We categorize the RPM of the pedal into "slow", "medium", and "fast". These values correspond to shifting up/down a gear on the bike, which is communicated to a microcontroller to shift the gear-shifting lever on the middle frame of the bike.

I designed the gear system that interfaces with 2 servo motors to shift the lever on the bike. I also designed the mounting system that attaches the moving parts to the bike frame, as well as the ultrasonic sensor mounts near the bike pedals. The systems were manufactured with a combination of laser-cut and 3D-printed parts.

I started with a CAD model of the bicycle from IRL measurements an a IR 3D scanner app.

I then designed and laser cut the servo brackets and gear system with minimal iterations.

Finally I made a ultrasonic sensor and ESP32 mount.

Automatic Gear Shifting Bicycle