Askari M., Komarizade M.H., Nikbakht A.M., Nobakht N., Teimourlou R.F., 2011. A novel three-point hitch dynamometer to measure the draft requirement of mounted implements. Res. Agr. Eng., 57: 128-136.An adjustable three-point hitch dynamometer with a draft capacity of 50 kN was developed to measure forces on the tractor and mounted implements. The design concept of the dynamometer was based on two linkage frames mounted between tractor links and the implement. The force sensing elements were comprised of a loadcell that was installed between the frames. The system provides variable width and height of the dynamometer links to satisfy a wide range of implement dimensions. All mounted tillage implements at categories II and III such as plows, cultivators and harrows were able to be tested by this dynamometer excluding mounted implements powered by power take-off (PTO). The dynamometer was calibrated and several field tests were conducted to measure the force required to pull a moldboard plow in a clay loam soil. The calibration showed a high degree of linearity between the draft requirements and the dynamometer outputs. Field tests showed that it was able to function effectively as intended without any mechanical problems.

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The present study is aimed at determination of the super-elliptic shape of tire-soil contact area using image processing method. Contact area has a substantial role on determination of soil compaction and tractive parameters of agricultural tractors. A very well-known model in this realm is to describe the contact area with superellipse geometry. A soil bin testing facility equipped with a single-wheel tester was utilized to conduct the needed experiments. The experiments were carried out at three levels of wheel load, three levels of tire inflation pressure with three replicates in a completely randomized block design. Corresponding images were taken for each of the experiments and the images were processed accordingly. The contact length and width were determined using imdistline command in MATLAB commercial software. This experiment was conducted at three levels of wheel load (2, 3, and 4 kN), and three levels of tire inflation pressure (100, 200, and 300 kPa) with three replications. The aforementioned parameters were applied consequently in the superellipse model and the contact area was computed. The obtained results disclosed that increase of wheel load increases the contact area. Contradictory, increment of tire inflation pressure reduces the formed contact area. Additionally, the potential of contact area determination with the proposed model was compared with that of actual values, which denoted coefficient of determination equal to 0.96, which shows the promising ability of the proposed model and the appropriateness of describing contact area with superellipse geometry