1, Design requirements
In view of the advantages of tracked vehicles in mountainous terrain without roads, the self-propelled tracked transporter is a useful supplement to the existing orchard transportation methods, which can enhance the adaptability and mobility of short-distance transportation and better solve the transportation problems of mountainous orchards. Different from the traditional design method of miniature tracked transporters, combined with the complex terrain in mountainous areas, due to the low speed of the vehicle, the rollover is designed with rigid quasi-static rollover, and the following design requirements are proposed.

(1) The design of the crawler chassis structure should be conducive to improving the passability of the transporter in the mountain orchard, i.e. having better steering performance, stronger climbing ability and anti-rollover ability.
(2) The design of the steering and travel control system of the crawler should be conducive to improving the maneuverability and adaptability to mountain orchard transport operations.
(3) The matching of the power transmission system of the transport machine should be conducive to improving the tractive force, load-bearing capacity, transport efficiency and fuel economy of the transport machine.
(4) The optimized design of the carriage structure and the layout of the whole machine, to improve the versatility and adaptability of the transporter and reduce the cost of use. Therefore, the specific technical parameters of the design are as follows: large climbing degree of 20, large load capacity of 250kg on flat ground and 150kg on slope; two forward gears, speed of 1.4-3.5km/h, and one reverse gear, which are required to have good anti-rollover performance under various load conditions.

2 Anti-rollover design of the overall arrangement of the vehicle
The overall design of self-propelled crawler truck should have a reasonable layout and compact structure because it needs to work under high load conditions in addition to the ability to drive in mountainous areas. In terms of dynamics, it should have enough driving power to obtain good acceleration, climbing and obstacle-crossing performance, and it is also extremely important to improve the safety and stability of the crawler. Since the size of the vehicle is relatively small and the size of the tracked chassis is limited, it is easier to roll over than medium and large tracked vehicles when driving on uneven roads in mountainous and hilly areas, so it is especially important to improve its anti-rollover performance under various loads.

According to the design requirements, the following design principles are adopted for the overall arrangement of the vehicle in order to improve the rollover resistance of the self-propelled tracked transporters.
(1) Adopt a simplified design of the running system, which consists of integral rubber tracks, driving wheels, supporting wheels, tensioning wheels and their tensioning mechanism; the rubber tracks are light in weight, and the sag above the tracks is small when driving, so they can not be equipped with carrier wheels; because the design speed is low and only the cargo is carried, the suspension device necessary for medium and large tracked vehicles can be omitted in the design, thus reducing the weight of the vehicle and facilitating the anti-skid and rollover. Therefore, the weight of the vehicle can be reduced, which is good for anti-skid and rollover.

(2) Adopting ultra-low-speed gear train design with two-shaft transmission and central gear main reducer, the crawler truck has large enough driving force and ultra-low-speed output performance, which is conducive to improving the passing performance and the anti-rollover capability.

(3) In order to make the mass distribution of the whole vehicle even and reasonable, and to facilitate the driving on the complicated road with uneven mountainous terrain, and to improve the anti-rollover performance, the ground clearance height of the transport vehicle and the position of the center of gravity of the whole vehicle must be taken into account, the chassis frame adopts H-type structure, and the engine and transmission are placed on the drive wheel side, i.e. the same platform at the rear of the frame, and the main reducer housing is fixed on the frame and placed at the lower part of the engine and transmission. The engine transmits power to the transmission through the belt drive, and the output shaft of the transmission transmits power to the central gear of the main reducer through the gear drive, and the power is transmitted to the half-axle and the driving wheel of the track through the steering clutch which is always engaged to realize the driving of the tracked transport vehicle. The carriage for transporting goods occupies the middle and front part of the frame, which makes the front and rear counterweight of the truck more even when it is fully loaded and helps to improve the anti-rollover performance.

(4) The handrails, shift handle, clutch, throttle and other mechanisms of the truck are designed according to the height of the human body to meet the general height of the handrails, making the operation more comfortable and convenient; the size of the carriage is designed according to the size of the standard basket for transporting fruits, and in order to increase the loading volume, the carriage has different degrees of size expansion in the left and right and front and rear directions through the design of the expansion plate, which improves the loading capacity of the fruits, and the position of the center of mass under different loading loads is conducive to improving the anti-rollover performance.