## 3 Results and Discussion  
The tests involved determining the coordinates of the collision point with the sensor surface and the relative error of the sensor detection indications for grains fed into the seed delivery tube. Based on the results, changes in the values of the collision point coordinates and grain flight length along with the tilt angle were observed which is presented in Figures 7, 9 and 10. Experimental tests of straight and diagonal exit ends provided high values of the correlation coefficient for collision points \(X\) and \(Y\) and grain flight length \(X_{0}\) (Table 3), though not all values were statistically significant which could have been caused by a small sample size (four values of tilt angle). An analysis of correlation showed that for the straight exit hole the coordinate of the grain collision with the sensor in axis X and grain flight length were positively correlated with the tilt angle, whereas the collision point coordinate in axis \(Y\) was negatively correlated (Table 3). In the case of a diagonal opening, coordinates of the collision point in axis \(X\) and \(Y\) were negatively correlated, whereas the flight length was correlated positively with the tilt angle (Table 3). Similar correlations between the variables were obtained for the straight exit hole from a simulation analysis in RockyDEM (Table 4). For the diagonal exit end, the results of a correlation analysis in DEM simulation differed from those obtained from the experiment. Contrary to experimental tests, there were negative correlations (though statistically insignificant), between the collision point coordinates on axis \(Y\) and the grain flight length after the impact (Table 4). Comparing the values of the collision point coordinates and the coordinate of the grain flight finish provided by DEM simulations and experimental tests for different exit ends and tilt angles it should be said that the results are similar, however, some differences occurred which is reflected by the non-overlapping ranges of the values of the coordinates presented in Figures 9-11. These differences can be the effect of simplifications of the models used in the simulation software, calculation errors, and the uncertainty of the simulation input data. In this case differences in the collision points and grain flight length in experimental and simulation tests are caused mostly by initial assumptions and input data regarding the feed material [42]. A constant grain diameter equal to 2.2 mm was assumed and the rape grain shape was assumed to be an ideal sphere. In reality, rape grains differ in terms of size (diameters in the range 1.8-2.2 mm) and shape as sometimes theydo not make ideal spheres. Seeds of biological materials are characterized by significant shape diversity within one species and a wide range of values for one feature, as found in previous studies [43; 44]. Diversity of the grain shapes has a significant influence on the grain flight destination point because the grain shape includes, among others the following: angle of impact with the sensor surface which affects the length of flying as well as inertia moments that cause rotation of the grain around its own axis upon collision. Moreover, the impact parameters are affected by the coefficients of restitution, rolling, and dynamic friction accepted in the simulation which in reality are not constant for rape grains, and in this case a constant value was accepted for each grain in the simulation. As proven in [45], the coefficient of restitution, depending on the grain size, allows the grain speed after the impact to be determined which in turn has a large influence on the grain flight range. Figure 10: Grain collision point measured in \(Y\) axis for different tilt angles—experimental and simulation results. Figure 9: Grain collision point measured in axis \(X\) for different tilt angles—experimental and simulation results.