design, construction and calibration of an adjustable three-point hitch dynamometer for common agricultural tractors in iran

this study describes the design, construction and calibration of an adjustable three-point hitch dynamometer. the dynamometer frame design was based on an inverted u-shaped frame that was mounted between the tractor links and implement. the dynamometer frame design allows for use in both category i and ii three-point hitch systems because of its flexibility in a lower point hitch spread and mast height adjustment. the dynamometer was designed to measure the maximum resultant horizontal and vertical forces of 50 kn and 30 kn, respectively. the force sensing elements comprised three steel extended octagonal ring transducers located between the frame and implement. electrical resistance strain gauges were installed on the extended octagonal ring transducers at strain angle nodes to monitor draft and vertical forces independently at the ring center. the data acquisition system consisted of a dt800 programmable data logger and a laptop computer. field tests on the dynamometer and data acquisition system showed that they were able to function effectively. the field experiments to collect data for evaluation of the three-point hitch dynamometer were done using a subsoiler. field tests were conducted at soil moisture levels of 21.2 and 9.2% at two operating tillage depths with four replications. a t-test was utilized for mean comparison of the three-point hitch dynamometer and drawbar dynamometer data. a drawbar dynamometer was installed between the two tractors which the front tractor used to pull the tractor with a three point hitch dynamometer and the subsoiler connected to the dynamometer. the advantages of the three-point hitch dynamometer make it advisable for horizontal and vertical force components measurement at production fields for common agricultural tractors in iran.