Abstract
From the viewpoint of when and why railroad axles started to rotate, early locomotives are reviewed. Conjectural replicas of locomotives produced by Richard Trevithick, William Hedley, George Stephenson, Robert Stephenson, and locomotive Planet in the United Kingdom were photographed. The first steam locomotive, Penydarren, in 1804 by Richard Trevithick started axle rotation. However, the replica of Stevens in 1825 by John Stevens in the US displayed in the Museum of Science and Industry has axles which are wooden square ones and do not rotate. In 1812, there was an adhesion testing truck by William Hedley, and this tells that the adhesion between wheel and rail was an issue. Axles of automobiles and aircrafts do not rotate because the adhesion between rubber tire and road is enough for traction force. Railroad axles need to get enough adhesion by wheels connecting together through axles to obtain enough traction force because the adhesion between rail and wheel is small due to small contact area. Running together was accomplished by rotating axles. The locomotive Penydarren used the first rotating axles, and is admitted as the first locomotive in the world. This paper also explains axles and wheels of early locomotives in the US and Japan, and present technology of axles and wheels.
