# Development of a Combined Orchard Harvesting Robot Navigation System
## 4 Discussion  
The distance between apple tree plants is about 2 m. When the transport or picking robot is between apple tree rows, each driving distance is about one plant distance, and too fast a speed leads to larger inertia when the robot stops, thus affecting the following error of the joint picking autonomous navigation system. At the same time, when the robot speed is too fast, the central control unit cannot provide the transport robot with accurate positioning point information in the middle of the apple tree rows. After a preliminary practical test, the driving speed of the robot was set to 0.5 m/s during the experiment. 1. The experimental results of the communication system showed that the master-slave robot can send messages via point-to-point in the orchard. Although the information interaction between master and slave robots showed communication packet loss as the communication distance increased, when the distance between robots (50 m) was greater than the maximum distance of a single row of apple trees (47.4 m), the packet loss rate of the communication system was less than 1.2% and the number of packet losses was negligible. This indicates that when the combined harvesting robots traveled in the middle of the apple tree rows within 50 m, there was little medium to affect the communication between the robots in the space above the weeds under the tree canopy. Although the distance between robots changes during travel, the distance interval is typically less than 10 m, which means that the master-slave robot can maintain operation within the communication distance of a strong signal. Thus, a Wi-Fi-based master-slave robot communication system can meet the communication needs of collaborative operations in orchards. 2. The position deviation values of the master and slave robots decreased as the number of trials increased when the combined harvesting robot was driving in the orchard rows, For example, the position deviation of the master robot decreased from 0.027 m  
Figure 18: Results of autonomous navigation experiments with transport and picking robots. (**a**) Stopping points of the transport robot; (**b**) stopping points of the picking robot; (**c**) heading deviation between transport and picking robots; (**d**) lateral deviation between transport and picking robots. to 0.02 m, which may be because the robot's tracks flattened the weeds and floating soil on the ground during repeated driving in the orchard, thus reducing soil-induced slippage. However, the average value of position deviation of the slave robot increased from 0.037 m to 0.048 m, which may be because during the turning process the master-slave robot switched to command navigation, and as the master robot pulled the trailer to turn, the heading of the trailer changed significantly, resulting in a larger angle of heading change when the robot turned from the ground for the next row (the heading difference between the master-slave robot was greater than 10\({}^{\circ}\) less than 90\({}^{\circ}\)). This, in turn affects the size of the position deviation. For example, at the first stop in the next row, the maximum value of the position deviation was 0.397 m. The position deviations of the master and slave robots varied considerably at the stopping point, which was either the next or the previous point of the one-sided apple tree stopping point. For example, in the first row, the maximum value of position deviation was 0.019 m at station 12 (lack of apple trees) and 0.053 m at station 13, which could be due to the change in canopy density from dense to sparse, or from sparse to dense. This variation led to deviations in the trunk centroids identified by the master robot and caused position deviations in the slave following the master. The position deviations at both ends of the apple tree rows were mostly smaller than the average deviation, probably because there was no interference from other apple trees and the trunks of the apple trees were thick enough for the master robot to identify the trunks.