From the Collections: Horsepower at Iowa State

A team of horse are hitched to the rear of a modified truck. A group of men are standing on the truck bed along with some equipment. An early form of the dynamometer is being used to test the horses' pulling power.
Horse dynamometer trial run. (University Photographs, 09-07-F.AgEngr.554-02-011)

In the early 1920s, Iowa State pioneered a new measurement of horsepower by inventing a machine that could measure the pulling strength of a team of horses. Earlier horse dynamometers measured only the force required to move a load, not the force required to start pulling a load.

A technical drawing of a dynamometer by E.V. Collins and approved by Jay Brownlee Davidson. The drawing shows the dynamometer from the side and has an annotation of "Pat. applied for."
Technical drawing of a dynamometer. (Jay Brownlee Davidson Papers, RS 9/7/11. 09-07-11_Davidson_0016-004-001)

The device, “Iowa Dynamometer Car for Horses,” was patented by E. V. Collins and J. B. Davidson in 1926.

More agricultural engineering materials can be found in the Agricultural and Biosystems Engineering Digital Collection and at the Department of Agricultural and Biosystems Engineering space in the Digital Repository.


College of Agriculture and Life Sciences. “Department of Agricultural and Biosystems Engineering 125th Points of Pride,” August 1, 2017.

Palmquist, John Gustaf, “A drawbar dynamometer for direct reading of horsepower” (1949). Retrospective Theses and Dissertations. 16325.


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