Video Description: Reuleaux's rotor: How Round is your Circle? Where Engineering and Mathematics Meet by John Bryant and Chris Sangwin.
 
Content Creator: John Bryant and Chris Sangwin at How Round is your Circle

A Reuleaux polygon is a curve of constant width - that is, a curve in which all diameters are the same length. The best-known version is the Reuleaux triangle. Both are named after Franz Reuleaux, a 19th-century German engineer who did pioneering work on ways that machines translate one type of motion into another, although it was known before his time.