# Design and Test of Vertical Axis Rotating Cutters for Cutting Corn Roots and Crown
## 3 Results and Discussion
### Results of the Full-Factor Test  
#### 3.2.1 Effect of Different Factors on the Qualified Rate of Root-Crown  
According to Table 2, the mathematical model relating the forward speed and rotational speed of the cutter shaft to the qualified rate of root-crown length was significant (\(p<0.01\)). The effect of both the forward speed and the rotational speed of the cutter shaft on the qualified rate of root-crown length was significant (\(p<0.01\)). And there were interactions between them (\(p<0.01\)).  
As shown in Figure 7, when the forward speed of the device was kept, the qualified rate of root-crown length increased with the increase in the rotational speed of the cutter shaft. The reason was that as the rotational speed of the cutter shaft increased, the linear velocity of the cutters increased. Therefore, the kinetic energy of the cutters also increased; the force generated by cutters on the crown also increased. Due to the supporting effect of the moving-fixed cutters and soil on the root-crown, forces in different directions were applied to different parts of the root-crown, which led to the effect of tearing the root-crown and further improved the qualified rate of root-crown. Simulation data demonstrated that this special curved cutter could deduce corn crown sliding along the edge of the cutter, and the qualified rate of corn crown length after cutting would be improved during low-speed operations, which fully validated the rationality and superiority of the bionic structural design. When the rotational speed of the cutter shaft was kept, the qualified rate of crown length decreased with the increase in the forward speed of the device. The reason was that the increase in forward speed had a smaller effect on the kinetic energy of the cutters [34];  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **df** & **Mean Square** & **F Value** & **\(p\)-Value Prob \textgreater{} F** \\ \hline Model & 0.15 & 24 & 6.305 \(\times\) 10\({}^{-3}\) & 346.30 & \textless{}0.0001 \\ A & 0.042 & 4 & 0.011 & 577.07 & \textless{}0.0001 \\ B & 0.10 & 4 & 0.026 & 1402.23 & \textless{}0.0001 \\ AB & 7.175 \(\times\) 10\({}^{-3}\) & 16 & 4.484 \(\times\) 10\({}^{-4}\) & 24.63 & \textless{}0.0001 \\ Pure Error & 9.104 \(\times\) 10\({}^{-4}\) & 50 & 1.821 \(\times\) 10\({}^{-5}\) & & \\ Cor Total & 0.15 & 74 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: The mathematical model relating the forward speed and rotational speed of the cutter shaft to the qualified rate of root–crown length.  
Figure 6: The process of cutting the root–crown.  
however, the cycloidal trajectory of moving cutters was significantly affected. As the forward speed increased, the swept area of the cutters was decreased. This would result in missed or incomplete cutting of the root-crown; therefore, the qualified rate of root-crown would decrease [34; 35]. The operational efficiency of the device would be affected by low forward speed; therefore, improving the qualified rate of the root-crown length under a high forward speed would be a key technical challenge for future agricultural machinery research. When the forward speed was 0.71 m\(\cdot\)s\({}^{-1}\) and the rotational speed of the cutter shaft was 540 r\(\cdot\)min\({}^{-1}\), the qualified rate of root-crown length was highest, and the value was 98.51%. When the forward speed was 1.43 m\(\cdot\)s\({}^{-1}\) and the rotational speed of the cutter shaft was 360 r\(\cdot\)min\({}^{-1}\), the qualified rate of root-crown length was lowest, and the value was 83.13%. According to the national standard, the qualification criterion requires that the length of the root-crown should not exceed 10 mm, and the qualified rate of root-crowns should not be lower than 90% [36]. Therefore, the operating range of the device that met the criteria was as follows: the forward speed ranged from 0.71 m\(\cdot\)s\({}^{-1}\) to 1.2 m\(\cdot\)s\({}^{-1}\) and the rotational speed of the cutter shaft ranged from 460 r\(\cdot\)min\({}^{-1}\) to 540 r\(\cdot\)min\({}^{-1}\).