Rich Olson built this ducted fan bike using model airplane motors and an Arduino:

Normally the motor controllers are connected to a receiver – but I wanted something a little less cumbersome. So – I rigged up an Arduino to generate a PWM signal – and tossed together a little control panel.

The battery is a big sealed lead acid (SLA) 12v. It’s good for 18 amp hours – but that’s assuming the energy is consumed over a 20 hour period. When SLA’s are drained quickly – they only provide a fraction of their total capacity. I’ll make up a number – and say I’m getting maybe 5 amp hours.

[Via Hacked Gadgets]