*5.2. Calibration of the RFCP-B*

After the calibration of the RFCP-P, the repose angle test was also used to calibrate the RFCP-B. In this paper, spheres with the same boundary material were processed, with a radius of 5 mm. The soybean seed particles and organic glass balls were 350 g each. They were uniformly mixed and poured into the loading box for testing, and the repose angle was simulated and analyzed, as shown in Figure 14. The rolling friction coefficient between the soybean seed particles and organic glass spheres obtained from the calibration was the RFCP-B.

**Figure 14.** Test and simulation diagram of the repose angle of soybean seed particles mixed with organic glass spheres.

The static friction coefficient and rolling friction coefficient between the organic glass spheres and boundary involved in the simulation were measured by the slope method, and the restitution coefficient was measured by the drop test.

#### *5.3. Analysis of Results*

5.3.1. Calibration Results of the RFCP-P

The relationship between the angle of repose and the RFCP-P for the three varieties are shown in Figure 15.

**Figure 15.** The relationship between the angle of repose and the RFCP-P for (**a**) SN42, (**b**) JD17, and (**c**) ZD39.

For the three varieties, the angle of repose tended to increase as the RFCP-P increased. The repose angle results for the three varieties (SN42, 23.86◦; JD17, 27.78◦; and ZD39, 38.97◦.) were obtained by measuring the repose angle test of the soybean seed particles. Taking SN42 as an example, the relationship between the angle of repose and RFCP-P was obtained by liner fitting, and the formula is shown as follows.

$$\mathbf{y} = 174.2\mathbf{x} + 18.398\mathbf{s}\ \text{(R}^2 = 0.9298) \tag{8}$$

The result (23.86◦) of the repose angle test for SN42 was entered into Formula 8, and the RFCP-P was calculated to be 0.031. The same method was used to calculate the RFCP-P, which was 0.018 and 0.136 for JD17 and ZD39, respectively.
