## 3 Results and Discussion
### Power Consumption of Thresher Device  
Some studies have shown that the threshing power consumption is subject to both the changes of feed rate and the type of threshing drum [30; 31]. To differentiate the impacts to threshing power consumption brought by both adjustment methods for threshing gap, traditional threshing drum was adopted in concave adjustment type while variable-diameter drum was adopted in threshing drum adjustment type. Under the forward speed of 1 m/s, analysis was implemented on the results of power consumption obtained from the experiments with both adjustment methods in two cases, i.e., the threshing gap was increased by 10 mm (30 mm) and decreased by 10 mm (10 mm), respectively.  
As shown in Figure 9(a), when the threshing gap was increased to 30 mm, the threshing power consumption with concave adjustment type features rather high fluctuation range upwards and downwards, in which the maximum power consumption was 48.31 KW and the average power consumption was 28.73 KW. In addition, the instant threshing power consumption was not stable, and the curve was not regular. The curve for threshing power consumption with threshing drum adjustment type has an outline in the form of trapezoid with relatively stable curve fluctuation. The maximum power consumption was 54.15 KW and the average power consumption was 34.83 KW. As shown in Figure 9(b), when the threshing gap was decreased to 10 mm, the maximum power consumption with concave adjustment type was 51.71 KW and the average power consumption was 30.22 KW. The maximum power consumption with threshing drum adjustment type was 59.53 KW and the average power consumption was 36.21 KW. The fluctuation ranges of threshing power consumption curve for both concave adjustment type and threshing drum adjustment type were relatively large, while the curve fluctuation with threshing drum adjustment type was relatively stable. This is because the decrease of threshing is relatively small at this moment and blockage may occur to the drum. On the other hand, the decrease of threshing with threshing drum adjustment type is even, therefore the fluctuation of power consumption curve is more stable and the shape is more regular, similar to a trapezoid.  
Figure 10: Diagram for the comparison in terms of threshing power consumption between both adjustment methods at the forward speed of 1 m/s, the red line is threshing drum adjustment type, the black line is concave adjustment type: (**a**) Threshing drum adjustment type and concave adjustment type with the threshing gap of 30 mm; (**b**) Threshing drum adjustment type and concave adjustment type with the threshing gap of 10 mm.  
In general, the fluctuation of threshing power consumption curve with concave adjustment type was relatively large and the curve was not regular. In the meantime, the fluctuation of threshing power consumption curve with threshing drum adjustment type was stable and the outline of the curve was in the shape of a trapezoid. This is because that with the concave adjustment type, the threshing gap within the thresher device is not even and the material conveying capacity of the thresher device is relatively poor. The threshing power consumption with concave adjustment type was smaller than that with threshing drum adjustment type. This is because that the concave adjustment type adopts traditional threshing drum which is relatively lighter. However, the threshing drum adjustment type adopts the variable-diameter drum which is heavier and results in higher power consumption. Threshing power consumption is related to the threshing gap and the quality of the threshing drum, lightweight treatment should be considered in the successive studies, thus to decrease the weight of the drum.