Considerations to select an existing vehicle to were based on the following criteria: reliability, durability and size. It should be noted that if a suitable vehicle were not found, a vehicle would be designed and produced to meet the system requirements.
The first limiting criteria of the vehicle is its size, by ensuring the size of the vehicle was kept to a minimum, the system would be capable of providing an increased range of functionality. The small size would be particularly useful around trees, gateways and orchards. Within New Zealand, Kiwifruit orchards are abundant with the vines laced overhead into a canopy. According to Philip Martin (personal communication 30 September 2015, Appendix K) from Plant & Food Research Limited stating that typical dimensions for mature kiwifruit blocks have a canopy height of 1.8 meters with a row width of 3.5 metres. Therefore, a vehicle used in this environment would be required to have a small vertical height. While this system is not designed to specifically for Kiwifruit orchards, the use of a smaller test vehicle was deemed not to reduce the functionality of the vehicle, except in the area of towing capacity.
Farming vehicles within New Zealand have be capable of meeting the rough requirements of the local landscape, with the Quad bikes, Mules and Tractors used within the New Zealand farming industry meeting these requirements. Working within the New Zealand environment requires high mechanical reliability, with any vehicle used by farmers that provides a simple mechanical design will provide the best platform, therefore an older model of such vehicles that has had proven reliability within the industry is required. Older models also provide a familiarity within the industry, and farmers know how to us, repair and maintain these vehicles.
These older models also provide more of a challenge, with newer models including on board computers, which while offer existing interface and sensor measurements, also provide reduced reliability as these parts make trouble shooting more difficult. Therefore, a system that is as basic as possible is required to cover the widest range of vehicles that this system could be applied to, and thus a manual gear changing system should be selected.
For this platform to operate effectively within the intended agricultural environment, it must be capable navigating rough terrain, including potholes, shallow ditches and small to moderate inclines, all while providing a stable platform on which this system can control and operate. To ensure maximum stability a vehicle featuring at least four wheels should be used and be outfitted with a drive system capable of providing sufficient power to navigate within
the expected operating environment; this includes sufficient power to tow additional equipment such as sprayers and other equipment.
The vehicle should be capable of performing sustained operations for several hours; therefore, a petrol driven vehicle is preferred as it can undertake long periods of operation out in the field away from external power sources. Petrol motors also generate onboard power via an alternator, which ensures power to the control system will be maintained, though this power may be interrupted for short periods during high power draw applications, such as starter motor activation. However, petrol driven systems cannot be operated within enclosed indoor environments over long periods due to possible health risks to humans and animals.
5.1.1
Existing Farming Vehicles
Three types of vehicles commonly used within the New Zealand farming industry are quad bikes, Mule and tractors, with the size constraints limiting the tractors available for selection. There are also a number of self-driving tractor systems available on the market, these could be integrated into this system and would reduce development time.
Quad bike (Figure 5-1) and Mule (Figure 5-2) provide smaller system platforms with the advantage of a tighter turning radius over larger vehicles. The smaller vehicle size ensures increased manoeuvrability due do the reduced distance between the wheel axles. Both the mule and quad bike will act as suitable platforms for this system, though the wide availability of second hand quad bikes was the deciding factor in the vehicle selection.
Figure 5-1 HONDA TRX250TM[21] Figure 5-2 KAWASAKI MULE™ 3010[22]
Quad bikes are abundant within the New Zealand farming industry, particularly within livestock farming and are used for the spraying of fields and orchards. Quad bikes have an advantage over mules due to their long history of use, providing users within the agricultural industry with a familiar platform to operate and maintain. This also allows users to upgrade their existing vehicles, reducing the initial system cost, which will likely increase the uptake of any system developed. Because of the manual control capabilities that this system will maintain, farmers will not have to lose this existing piece of farming equipment and if a new integrated system were obtained, the user would gain a new vehicle entirely.
There are a number of other advantages to this system in regards to user safety, with the system providing safety enhancements to the quad bike, including speed control depending on terrain conditions and cornering angle.
5.1.2
Selected Vehicle
A second hand quad bike was considered as the platform for this research, and provided a low cost vehicle frame to build on the desired system. A 1995 model, TRX-300 was purchased for this system. The motor and electrical components were still in working condition. The TRX-300 features fixed four-wheel drive with a manual gearbox, though this vehicle required extensive servicing to ensure it would be mechanically reliable. The bike features a 12-volt battery to power the on-board power systems, which is charged by an alternator when the engine is operating.
This servicing primarily involved repairing rusted out sections of the vehicle frame, with significant damage to the steering, rear deck tray, as well as many of the mounting struts. Parts serviced excluding the chassis framework included; the carburettor, front and rear brakes, rear axle, steering column and engine. This servicing ensured that all parts operated correctly and the system was structurally sound.