It was right after World War I during the height on the draft horse industry, when money was short, that the farmer bred draft horse to be used as the prime source of farm power. Professor E.V. Collins od Iowa State College was concerned about the efficient management of these work horses. In 1923-1926 he conducted research to learn the draft requirements of various implements and analyze what a good farm team could be expected to pull on a daily basis. This study was done to help the farmer better manage his available horse power. Professor Collins developed various machines to measure the working capacities of sound horses under different types of soil conditions. Collins writes, "Plowing requires more power than many other farming operations...the draft of a 14" plow plowing 6" deep in sudan grass requires 500 lbs. of tractive force," (draw-bar pull) which from the testing results recommends three horses.

In order to secure data on the maximum pulling power of horses, a machine was specially built and arrangements were made to conduct pulling contests in cooperation with various fairs and horse shows. The machine was so constructed that when a team was pulling, the presset weights were suspended in the air within vertical guides. An oil pump geared through the power takeoff was used to create resistence to the drag of the truck to thus maintain the equilibrium of the weights suspended by the towing cable. When the weights were hitting the top, the team was pulling with a force greater than that set on the machine; conversely, when the weights dropped to the bottom of the guides it meant the horse was not pulling at the set resistance. The contest was conducted in the following manner.

​The dynamometer was set for a tractive resistance which any good pulling team in his class could be expected to handle. A starting load of 1,500 pounds was used most frequently. Each team in turn was required to pull the dynamometer for a full standard distance of 27 1/2 feet without stopping. After all teams had either successfully completed this test or failed, the machine was set at increased resistance and all remaining teams tried until only one team could pull the maximum lead set on the machine. This final team was declared the winner.

Many people ask why 27 1/2 feet? The test were all conducted before the age of modern computers. Professor Collins, using James Watt's formula for horse power selected this distance to simplify his mathematics. Using 27 1/2 feet, the horse power developed reduced down to dividing 1/2 the "tractive pull" by ten times the number of seconds required to complete the distance or simply

                                           HP=1/2 (tractive pull)/10 t (t in seconds)

​For professor Collins, the contest gave him a better understanding of the importance of proper training, feeding, muscle conditioning and proper collar and harness fitting, with the fitting of the collar being most important. The value of good horsemanship was also clearly shown in all contests.

                                       Equivalents on the Dynamometer

MONTGOMERY — Local horse pull enthusiasts packed the State Line Area Saturday for the annual benefit horse and pony pull for St. Jude’s Children’s Hospital. The fundraiser raised $21,000 for the charity. “We had a real nice crowd,” event organizer Tom Brown said. “I want to thank all the community for all of its support.” The pull featured 20 pairs of ponies and 17 pairs of horses from as far away as Alberta, Canada. Other teams traveled from Indiana, Ohio, Wisconsin and Kentucky. The event was free, and donations were accepted. All of the food was provided by members of the Amish community.

Dynamometer History

History of the Draft Horse Dynamometer Machine

Determining pulling power In 1921, Professor E.V. Collins of the Agricultural Experiment Station at Iowa State College began tests to determine the work capacity of horses. Although dynamometers were available, they only measured the force required to move a load. This varied because of the surface upon which the load was pulled and because the force needed to start a load is much greater than that required to keep it moving. In order to accurately measure a horse’s pulling power, Professor Collins had to devise a machine that would require the same tractive pull to start it as to keep it in motion.
Collins started with an early International Harvester Auto Wagon with the engine, transmission and body removed, although the drive train and brakes were retained. A single tree was attached to a cable on each side, running over pulleys to the rear of the wagon, where a weight bucket was suspended on the end of each cable. If a horse was hitched to each of the single trees and the team was driven forward, the weights would rise in their guides until they reached the end of the vertical travel, at which time the wagon would also move forward. To keep the load constant, some resistance to the wagon’s forward motion was needed.  
To provide that resistance, a rotary pump was mounted so it was driven by the vehicle’s jack shaft sprocket. The pump inlet was piped to the bottom of a 10-gallon tank. Another pipe ran from the top of the tank to a rotary control valve and then to the pump outlet. This valve, when closed, prevented the fluid from circulating and the pump from turning, effectively locking the wagon’s wheels.
The valve was connected to the weights so that when the weights were at the bottom of their travel, the valve was closed and the wheels were locked, providing maximum resistance to the forward movement of the wagon. As the team pulled, the weights rose, gradually opening the valve, until at the top of the weight’s travel the valve was wide open and the wagon rolled easily. When calibrated correctly, the wagon would move just fast enough to keep the weights suspended while the team was moving.

Pulling for St. Jude's