Thomas Sheraton illustrated a chamber horse in his Appendix to the Cabinet-Maker and Upholsterer's Drawing-Book, London, 1802, pl. 22 and includes a drawing of the mechanism underneath the leather.
A chamber horse dating from circa 1760 with an interlaced splat back is in the Victoria and Albert Museum, London (illustrated in R. Edwards, The Shorter Dictionary of English Furniture, London, 1964, p. 174, fig. 1).