Self-Balancing Electric Unicycle. Stephan writes -

I recently built a partially self-balancing electric unicycle called “Bullet,” featuring:

• A custom MIG-welded steel chassis
• A 450 Watt electric motor
• Two 7 Ah 12 Volt batteries
• A 5DOF intertial measurement unit
• The OSMC H-bridge
• An ATmega328P microcontroller

I say “partially” self-balancing because it only balances along one axis (forward/backward), and the rider still needs to balance left and right (it’s analagous to riding a bicycle “no hands”). It operates much like a Segway — you lean forward to accelerate, and lean back to brake. The top speed is about 15 mph, and it easily goes 5 miles on a single charge. This is my primary mode of transportation on the MIT campus.