Quadricycle

The Eleventh Doctor assembled a quadricycle in 2013 from parts he found in Clara Oswald's garage, believing it to have been broken. When questioned, he realised that he had actually just invented it. (TV: The Bells of Saint John)
 * In the real world, the Doctor did not, in fact, invent it. In fact, 's first automobile in 1896 was called a 'quadricycle', due to its four-wheeled nature.