Mountain E-Bike

Overview

This project transforms a standard mountain bike into a powerful, well-balanced electric trail machine. Instead of using the hub motor in the wheel as intended, the motor was re-engineered and mounted at the center of the frame, effectively converting it into a mid-drive system.

A custom bracket was designed and fabricated to hold the motor securely at the bike’s core. To ensure smooth pedaling, a special sprocket with an integrated one-way bearing was added. This allows the motor to drive the rear wheel through the bike’s existing gear system without causing the pedals to rotate when the motor is running.

The battery was mounted on the top frame tube for easy access and good weight distribution. By placing the motor centrally and the battery high but centered, the overall center of mass remains balanced, maintaining the natural handling of a dirt-style mountain bike.

The result is a unique E-Bike with strong climbing performance, preserved gearing, and excellent off-road stability.

Key Features

Custom mid-drive motor conversion using a repurposed hub motor
Fully machined center-mount bracket for structural strength
One-way bearing sprocket prevents unwanted pedal rotation
Motor power routed through the rear cassette for full use of bike gearing
Battery mounted on top frame tube for accessibility
Balanced weight distribution for off-road riding
Retains natural “dirt bike” riding dynamics

Challenge

Hub motors are not designed to operate outside the wheel. Adapting one into a mid-drive system introduces multiple challenges: -Precisely positioning the motor at the bike’s center -Creating a rigid, vibration-resistant mount -Transferring motor torque into the chain without affecting pedaling -Maintaining correct chain alignment -Ensuring the bike stays balanced for aggressive mountain riding

Solution

-Designed a custom mid-frame mounting system for the hub motor -Added a one-way bearing sprocket, allowing motor-driven movement without back-driving the pedals -Leveraged the existing rear gears to maintain torque control and climbing power -Used CAD to model alignment, clearances, and load paths -Mounted the battery centrally to maintain the bike’s center of mass -Ensured all components were modular and serviceable