# Development of a Combined Orchard Harvesting Robot Navigation System
## 3 Results
### Communication Experiment  
To verify the reliability of information interaction of the combined harvesting robot in an orchard environment, based on the minimum tracking distance (0.35 m) between the two robots measured in the field and the longest distance (47.4 m) of the fruit tree rows in the test area, an orchard communication test of the combined harvesting robot was designed based on previous literature [38]. The test protocol is shown in Figure 15a.  
After the communication connection was established between the master and slave robots, it was first connected to the Internet Protocol (IP) address of the slave robot via the ssh command, and then 500 packets were sent to the master robots. The unreceived packets were checked on the computers connected to the IP address of the master robot at different  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Parameter** & **Average** & **Standard Deviation** \\ \hline Row spacing/m & 3.703–4.178 & 4.102 & 0.321 \\ Plant spacing/m & 1.876–2.155 & 2.055 & 0.107 \\ Diameter at breast & 0.32–0.53 & 0.417 & 0.066 \\ height/m & 0.40–0.61 & 0.531 & 0.070 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Apple-tree parameters of the apple orchard.  
Figure 14: Apple orchard experimental area environment. (**a**) Experimental area in Apple Orchard; (**b**) apple tree diameter at breast height measurement; (**c**) apple tree diameter at ground measurement.  
Figure 15: A combined harvesting robot communication trial. (**a**) Experimental scheme for master-slave robot orchard communication; (**b**) combined harvesting robot communication trials in orchards.  
distances, then the number of packets received by the slave machine was checked and the packet loss rate was calculated. This test was repeated five times independently. The IP address of the master robot at the time of the test was 192.168.62.2, and the IP address of the slave robot was 192.168.62.30.  
When the front end of the slave robot is 0.35 m away from the fruit basket of the master robot, the master robot can receive all the packets, and the number of packets lost and the packet loss rate of the communication system are both zero. The slave robot was then placed at 10, 20, 30, and 40 m from the master robot, which had 1, 2, 4, and 6 packet loss counts, resulting in the packet loss rate of the communication system being 0.2, 0.4, 0.8, and 1.2%, respectively. Finally, the slave robot was placed 50 m from the master robot, where the distance between the master and slave robots is greater than the length of the orchard rows, and the master robot was inside the orchard and the slave robot was outside the orchard. The number and rate of packet loss of this communication system were consistent with the distance interval of the robots at 40 m. It can be seen that the packet loss rate of data interaction within the orchard rows for the joint robots based on the communication system is less than 1.2%, which indicates that the data loss is negligible when the robots are interacting with information in the orchard.  
Data on the number of packet losses and packet loss rates for the robotic communication system tests are shown in Table S1 in the Supplementary Information.