History of the draft horse dynamometer machine
It was right after world war 1 during the height of the draft horse industry, money was short, that the farmer bred the draft horse to be used as the prime source of farm power. Professor E.V. Collins of Iowa State College was concerned about the efficient management of these work horses. In the years 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 any other one farming operation .... 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 preset weights were suspended in air within vertical guides . An oil pump geared through the power takeoff was used to create resistance to the drag of the truck to thus maintain equilibrium of the weights suspended by the towing cable. When the weights were hitting 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 horses were 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 1500 pounds was used most frequently . Each team in turn was required to pull the dynamometer for the 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 load set on the machine. The final team was declared the winner.
MANY PEOPLE ASK WHY 27 1/2 FEET?
The tests were all conducted before the age of the modern computer . Professor Collins , using James Watt's formula for horse power , selected this distance to simplify his mathematics for computing horsepower. Using 27 1/2 feet , the horse power reduced down to dividing 1/2 the "tractive pull" ( the reading on the machine) by ten times the number of seconds required to complete the distance , or simply----
HP= 1/2 (TRACTIVE PULL)
10t(t being 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.