epitrochoid Math.
(ɛpɪˈtrɒkɔɪd)
[f. Gr. ἐπί upon + τροχός wheel + -oid; after analogy of epicycloid.]
The curve described by a point rigidly connected with the centre of a circle which rolls on the outside of another circle. Cf. epicycloid.
| 1843 Penny Cycl. XXV. 284/2. 1879 Thomson & Tait Nat. Phil. I. i. §94. |
Hence epitroˈchoidal a., of or pertaining to an epitrochoid.
| 1800 Phil. Trans. XC. 149 Epitrochoidal curves, formed by combining a simple rotation or vibration with other subordinate rotations or vibrations. 1843 Penny Cycl. XXV. 284/2 Every direct-epicycle planetary system is both epitrochoidal and externally hypotrochoidal. 1959 Times 15 Dec. 7/1 The shape of the bore in which the triangular rotor revolves is described as epitrochoidal: the shield-shaped piston moves round the inside of a cavity like the hollow skin of an Edam cheese. 1969 Observer (Colour Suppl.) 23 Mar. 27/1 Take the revolutionary Wankel engine. Twin rotors in an epitrochoidal bore. That's two rotors going round and round, instead of four or more pistons going up and down. |