A motorized, fore-aft self-balancing transportation device that may include a single wheel structure with a drive motor, a battery and first and second foot platforms located on opposite sides of the wheel. The device may be uniquely be arranged such that the motor and battery are positioned such that there is space within the wheel envelope for a portion of the foot platform (positioned near or within the envelope), thereby placing the weight of the rider low and close to the center of gravity of the device. Various battery and motor arrangements are disclosed, as are different drive mechanisms and component redundancy to assure safe operation in the event of failure.