Epitrochoid, Kinematic Model by Martin Schilling, series 24, model 1, number 329
date: label: date made
content: ca 1900
name: label: maker
content: Schilling, Martin
notes: label: Description
content: Around 1900, American mathematicians introduced ideas to their students using physical models like this one. This model is the first in a series of kinematic models sold by the German firm of Schilling to show a mechanical method for generating mathematical curves.
label: Description
content: Circles rolling around the outside of other circles, known as epicycles to the ancient Greeks, were used to describe the motions of the planets in a geocentric cosmology. These curves,called epitrochoids, are formed by tracing a point on the radius or the extension of the radius of a circle as it rolls around the outside of a second stationary circle.
label: Description
content: Epitrochoids are members of the family of curves called trochoids, curves that are generated by tracing the motion of a point on the radius of a circle as it rolls along another curve. They include the cycloids (see item 1982.0795.05) and hypotrochoids (see items 1982.0795.02 and 1982.0795.03). In the 18th century, it was found that when shaping the sides of gear teeth as the valley between teeth, using trochoidal curves reduced the torque of the rotating gears and allowed them to rotate more efficiently.
label: Description
content: Depending on the distance of the tracing point from the center of the rolling circle, an infinite number of curves can be formed. The three curves depicted in this model are bicyclic, meaning the smaller circle needs to rotate around the larger circle twice before returning to is original configuration. The ratio of the radii of the two circles will determine the number of nodes in the curve and how many rotations are required before the tracing point returns to its starting configuration. The Spirograph toy produces various types of epitrochoids. (See item 2005.0055.02)
label: Description
content: In this model, a toothed metal disc of radius 30 mm links to a smaller toothed metal disc of radius 12mm. Rotating a crank beneath the baseplate rolls the smaller disc around the outer edge of the larger disk. The model illustrates three curves that may be generated by the motion of a point at a fixed distance along the radius of a circle when the circle rolls around the outer edge of a larger circle.
label: Description
content: The green point within the smaller circle (at radius 4mm) produces the green curve on the glass overlay of the model. The blue point on the circumference of the smaller circle (in this special case, the curve is known as an epicycloid) produces the blue curve. The third, represented by a red curve on the glass, is on the extension of a radius of the smaller circle (20mm). As the smaller circle rolls, the point moves inside the larger circle. The German title of this model is: Erzeugung der Epitrochoiden als solche mit freiem Centrum.
label: Description
content: References:
label: Description
content: Schilling, Martin, <i>Catalog Mathematischer Modelle für den höheren mathatischen Unterricht</i>, Halle a.s., Germany, 1911, pp 56-57. Series 24, group 1, model 1.
label: Description
content: Chironis, Nicholas, <i>Gear Design and Applications</i>, 1967, p. 160.
label: Description
content: Davis, W.O., <i>Gears for Small Machines</i>, 1953, p. 9.
label: Description
content: Grant, George, <i>Teeth of Gears</i>, 1891, p. 69.
label: Description
content: Material for educators can be found online at the Durango Bill website.
label: Description
content: Online demonstrations can be found at the Wolfram website Mathworld.
label: Location
content: Currently not on view
place: label: place made
content: Germany
topic: label: Subject
content: Mathematics
label: Subject
content: Engineering
setName: label: See more items in
content: Medicine and Science: Mathematics
label: See more items in
content: Science & Mathematics
label: See more items in
content: Kinematic Models
creditLine: label: Credit Line
content: Gift of the Department of Mathematics, The University of Michigan
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1982.0795.01
label: catalog number
content: 1982.0795.01
label: accession number
content: 1982.0795
objectType: label: Object Name
content: geometric model
physicalDescription: label: Physical Description
content: metal (overall material)
label: Physical Description
content: glass (overall material)
label: Physical Description
content: paper (overall material)
label: Physical Description
content: leather (overall material)
label: Measurements
content: overall: 5.8 cm x 22 cm x 27 cm; 2 9/32 in x 8 21/32 in x 10 5/8 in