## 3 Results and Discussion
The research program of the device for evaluating the suitability of varieties for mechanized harvesting of potatoes included field tests of potato harvesters and tests of the developed device in order to determine the mechanical damage to potato tubers when harvested by different potato harvesters and the corresponding damage to tubers on a simulator. Experimental studies to assess the force impact of working bodies on potato tubers were carried out on potato harvesters of the following brands: AVR-Spirit-6200 combine (Belgium), Dewulf RA-3060 combine (Holland) and Bolko combine (Poland). The methodology for conducting experimental studies is as follows. Before conducting experimental studies on the accounting plot, the physical and mechanical properties of the soil were determined: moisture and hardness, according to the method of STO AIST 8.7-2013 \"Machines for harvesting vegetables and melons. Methods for assessing functional indicators\". The technological parameters of the potato harvester before the research were set to optimal operating modes, in which the depth h_L of digging share into the soil was set below the depth of potato tubers in the range of 0.12-0.18 m, due to the planting depth of tubers. To carry out these studies, we set up a number of experiments when harvesting with potato harvesters: AVR-Spirit-6200 (Belgium), a Dewulf RA-3060 combine (Holland) and a Bolko combine (Poland), as well as during the operation of a tuber damage simulator, the technological schemes of which are presented in Figures 13-15. The determination of the mechanical damage of tubers during the experiments was carried out from each repetition of clean tubers weighing more than 50 g for damage analysis. The mass of the average sample was 10 kg. Four replicates were taken. During the analysis, the tubers were sorted into two groups: intact and damaged. Samples were taken in triplicate, and the percentage of damaged tubers was determined with a confidence probability of 0.95. The tuber tests on a simulator were carried out on the same day as experiments to determine damage when harvested by combine harvesters. Figure 14: Technological scheme of the combine “Dewulf RA-3060”: 1—rollers; 2—vertical disks; 3—plowshare; 4—main elevator; 5—defoliators; 6—cascade elevator; 7—additional elevator; 8—bucket elevator; 9—finger slide; 10—baffle element; 11—supporting tape; 12—shaft; 13—bulkhead table; 14—bunker. Figure 13: Technological scheme of the AVR-Spirit-6200 combine: 1—frame; 2—vertical disks; 3—digging share; 4—support wheel; 5—main elevator; 6—shaker; 7—cascade elevator; 8—finger slide; 9—bucket elevator; 10—bulkhead table; 11—bunker. The results of the studies between indicators of resistance to mechanical damage during comparative tests of potato harvesters and the work of a specially designed tuber damage simulator showed that there is a correlation between the damage of tubers when using the damage simulator and when harvesting with combines. Analyzing the graphical dependencies presented in Figure 14, we came to the conclusion that the minimum value of the level of damage in the considered section of the response surface with a factor is 7.34% and takes place at a combine operating speed of 1.875 km/h and when harvesting with a combine. The optimal values of the factors under consideration are within the operating speed of 1.64-2.11 km/h. Thus, the correlation coefficient for skin peeling is equal on average to 0923 and, according to the darkening of the pulp, 0.936 (Figure 16). When analyzing the research results, it was found that the maximum correlation is observed between the indicators of mechanical damage to tubers during the operation of combines and on the simulator for the following types of damage: cracks more than 20 mm long and darkening of the pulp more than 5 mm deep. Thus, it can be concluded that the simulator simulates drops, that is, impacts of tubers on the bar surface (darkening of the pulp and cracks), as well as the effect of separating organs (peeling).