Universal autopilot system of tractor based on Raspberry Pi

Abstract: With the process of industrialization, young workers pour into the city, the number of farm labor declines. The average age of farmers is increasing. The tractor, as a modern agricultural production machine, is one of the most important driving force sources of agricultural production. However, some drawbacks come with the manual control, such as, the uncomfortable working condition, the inaccurate routine and the operator fatigue. However, automated driving can improve the field operation standard, the utilization rate of the existing machinery, the mechanical efficiency and labor comfort. Therefore, designing a set of tractor automatic system has a significant meaning in terms of agriculture. At present, the majority of the tractor automated driving systems are designed for specified tractors. When a new type of tractor is used, the developers often need to upgrade their system in terms of software and hardware. And the monotonous work can be reduced by developing a universal system for all types of tractors. Professor Simon Blackmore has been working on a software system for tractors for more than 10 years, and this system can be used as a universal tractor control software system. However, a hardware system is still needed to cooperate with it. In the project, a distributed control system was developed for tractors. Raspberry Pi is used as ECU (electronic control unit) in this system, and TCP/IP (transmission control protocol/internet protocol) is used as the communication protocol in this system; laser distance sensors are used to monitor the environment of the tractor; a Heart Beat system is used to check every important part of this system to make sure the system runs properly. This system receives control commands from a Xbox wireless controller or SAFAR (software architecture for agricultural robot), and it responses to the control commands rapidly and correctly. The John Deere X534 tractor was transformed into automated tractor in the test, R2100 laser scanning distance sensor was selected to safeguard the security of information input system. Since John Deere X534 uses a light tractor CVT automatic transmission, the control strategy is to control the size of the throttle by a servo, and use a motor to control the tractor steering. Experimental results showed that the system was stable and reliable. Due to high precision and high frequency, R2100 laser scanning sensor made the security of the system greatly improved. In the test, when an object was close to the tractor, the tractor could timely stop to protect life and property safety. During the test, in the case of normal operation, disconnecting directly the TCP/IP interface, turning off the router and using other methods to make a fault in the system, the Heart Beat detection mechanism could immediately find the system fault, and Arduino Mega could make the speed set to 0 m/s and the steering angle set to 0 when other tractor control devices failed. The angle of the steering gear was changed in the experiment by changing the width of input signal (square wave signal, the frequency 50 Hz). The test results showed that this system could response to the operator or SAFAR rapidly and correctly, and the response time was about 0.5 s, which was highly acceptable for an off-road vehicle system. The communication between 3 ECUs was stable, dependable and fast. The safety system worked perfectly when any obstacle was found or any system error occurred. The experiment result shows that this system meets the requirement of this project significantly.