A hub motor is an electric motor built irectly into the hub of a wheel. A purported advantage of this design is that no additional transmission system is needed, thereby increasing the efficiency of the drive system. However, because electric motors are most efficient at high rates of revolution, direct drive hub motors tend to be inefficient. Integrated planetary gear drivetrains are sometimes included, but re-introduce transmission losses. They are commonly found on motorized bicycles. Hub Motor Electromagnetic fields are supplied to the stationary windings of the motor. The outer part of the motor follows, or tries to follow, those fields, turning the wheel to which it is attached. Energy is transferred to a brushed motor through physical contact of brushes to the rotating shaft of the motor. Energy is transferred to a brushless motor electronically, requiring no physical contact between stationary and moving parts. Brushless motor technology is more expensive, but most are more efficient and longer-lasting than brushed motor systems. Most of the hub motors made in China are designed for bikes with Chinese dimensions but these conversion kits are made to suit western bike dimensions. Hub motors are not a new idea. In 1902 Ferdinand Porsche at age 27 working for Lohner developed hub motors which initially ran on lead acid batteries and soon after had a petrol generator to charge the batteries: the first Hybrid vehicles. Hub motors can also be found on buses.