## 3 Results and Discussion
### Grain-Entrainment Loss Rate  
The grain entrainment loss refers to the free grain discharged together with the entrained stalks coming out of the straw outlet, which is one of the key specifications of the operation performance  
Figure 7: Real product photo for the assembled variable-diameter threshing drum, 1. Feeding wheel and adjustment device 2. Adjustment device for rear supporting wheel 3. Electronic control self-locking device. of the threeher device [25]. The comparison in terms of grain-entrainment loss rate under different forward speeds (feed rate) and threshing gaps with both adjustment methods is shown in Figure 8.  
The forward speed of 0.6-0.8 m/s was defined as low speed and the corresponding feed rate was relatively low; the forward speed of 1-1.2 m/s was defined as medium speed and the corresponding feed rate was normal; the forward speed of 1.4-1.6 m/s was defined as high speed and the corresponding feed rate was large [26]. It can be seen from the bar graph that the grain-entrainment loss rates under all the five different threshing gaps increased with the rising of the forward speed. Under low speed, the entrainment loss rates listed in ascending order are: initial gap of 20 mm, threshing drum adjustment type of 10 mm, concave adjustment type of 10 mm, threshing drum adjustment type of 30 mm, and concave adjustment type of 30 mm. Under medium speed, with the increase of forward speed, the entrainment loss rate with concave adjustment type of 30 mm remained the highest. The entrainment loss rate with threshing drum adjustment type with 10 mm and that with concave adjustment type of 10 mm exceeded the entrainment loss rate with threshing drum adjustment type of 30 mm. The entrainment loss rate with initial gap of 20 mm remained the lowest. Under high speed, the entrainment loss rate with threshing drum adjustment type of 10 mm was the highest, while the entrainment loss rate with concave adjustment type of 10 mm was in the second place. The entrainment loss rate with threshing drum adjustment type of 30 mm exceeds that with concave adjustment type of 30 mm and took the third place. The entrainment loss rate with initial gap of 20 mm was the lowest. The entrainment loss rate decreased at first and then increased with the increase of the threshing gap. This is because that with the increase of the threshing gap, the thickness of grain layer is thinned, and grain has increased possibilities to penetrate the grain layer. Therefore, the entrainment loss rate is becoming smaller gradually; while when the threshing gap is too large, the condition goes against the separation of grains, therefore the entrainment loss rate will go higher. It can be seen from the curve diagram that with the increase of forward speed, the entrainment loss rate with initial gap of 20 mm was the lowest all the time. However, the amplification trend of the entrainment loss rate under high speed was higher. The impact brought to the entrainment loss rate with threshing drum adjustment type of 30 mm featuring relatively higher threshing gap by the forward speed was not obvious. On the other hand, the impact to entrainment loss rate of the threshing drum adjustment type of 10 mm featuring the lowest threshing gap was the most obvious. Under low speed, the entrainment loss rate with threshing drum adjustment type of 10 mm was in second place and that with concave adjustment type of 10 mm took third place. However, with the increase of the forward speed, the amplification trend of entrainment loss rate with threshing drum adjustment type of 10 mm was higher than that with concave adjustment type of 10 mm. In addition, in the section from 1.2-1.4 m/s, the entrainment loss rate with threshing drum adjustment type of 10 mm became the highest by exceeding that with concave adjustment type of 10 mm. This is because within the thresher device, the threshing gap with concave adjustment type of 10 mm is larger than that with threshing drum adjustment type of 10 mm.