Double extended octagonal ring (DEOR) drawbar dynamometer

A drawbar dynamometer is required to measure drawbar forces in field research on energy inputs for agricultural field equipment. In this study, a 2D double extended octagonal ring (DEOR) drawbar dynamometer with a draft capacity of 180 kN was developed. The two extended octagonal rings were oriented vertically on either side of the tractor drawbar which provided a better match of strain to expected drawbar draft and vertical load than could be achieved with a horizontal orientation in previous designs. Strain distributions in the extended octagonal rings were analyzed using a finite element method to locate optimal strain gage positions to minimize cross sensitivity between draft and vertical force measurements. The DEOR was fabricated from high strength ANSI 4130 steel. Vertical and draft calibrations of the DEOR dynamometer were done in a laboratory universal testing machine. Calibration results show that the DEOR dynamometer had a linearity of 0.99 and negligible cross sensitivity for both horizontal and vertical outputs. The DEOR dynamometer was tested in a field to measure the draft and vertical force of a sweep-type liquid manure injector. No mechanical problems were observed for the dynamometer in the field test and its draft outputs were comparable to those reported in the literature for manure injectors.