Development of an electric vehicle for autonomous use on a New Zealand dairy farm. (2020)
Type of ContentTheses / Dissertations
Thesis DisciplineMechanical Engineering
Degree NameMaster of Engineering
PublisherUniversity of Canterbury
AuthorsPetterson, Timothy Clarrieshow all
With the increasing cost of employment and difficulty finding suitably skilled workers, autonomous vehicles are being implemented as a solution across a number of industries. On New Zealand dairy farms, simplistic tasks such as transporting feed and supplies, mowing, spraying and pasture measurement could easily be completed by a small autonomous vehicle. Pasture measurement is particularly important to maximize the farm’s productivity, but is often neglected as it consumes a significant quantity of time. Consequently, there is real demand for an autonomous vehicle to complete these tasks.
Ideally, this autonomous vehicle would be electric due to the reduced environmental impact, coupled with lower running costs, higher reliability and ease of control when compared to internal combustion (IC) equivalents. However, the major factors limiting the implementation of electric vehicles (EVs) in agriculture is their significantly smaller range (travel distance on one charge) and higher purchase price. For it to be worthwhile to utilize an EV to complete these autonomous tasks, it must produce a similar range when compared to an IC equivalent at a competitive price. It was identified during the EV’s development that producing the desired range was going to be very difficult due to the expensive nature of lightweight batteries limiting battery capacity.
An EV was developed, similar in size to a typical IC quad, which focused on maximizing its efficiency and minimizing vehicle weight and cost, whilst remaining a capable off-road vehicle. The developed EV was significantly lighter than similar sized off-road EVs, with suspension, traction and steering characteristics that matched or exceeded the performance of IC equivalents. This means that a very capable off-road EV can be developed. The developed EV produced a maximum powertrain efficiency of 84%. However, even with this high efficiency, further work had to be completed to maximize range within the limited battery capacity.
Due to the off-road environment and low operational speed of the EV, motion and rolling resistance are the only significant forces constantly opposing the EV’s motion. Motion resistance was investigated and it was determined that vehicle design and tyre selection had a major influence on the resistive forces experienced. A further study into rolling resistance was conducted, were it was found little was known about rolling resistance of small all-terrain vehicles (ATVs). Experiments were conducted and rolling resistance data was collected for seven ATV tyres. The obtained data confirmed and established relationships between rolling resistance, tyre properties, and operational and environmental conditions. It was determined that tyre selection has a major influence on the forces opposing the EV’s motion and, consequently, had a significant effect on the developed EV’s range.
The developed EV produced a significantly larger range (travel distance on one charge) than similar sized off-road EVs despite its much smaller battery capacity. This was due to the significant reduction of rolling and motion resistance through appropriate tyre selection and vehicle design. The developed EV was competitive with an IC equivalent, producing a 20km lower range at approximately the same vehicle price. With further developments in battery technology and the reduction of battery prices, the developed EV will be able to match or exceed the range of IC equivalents to produce a more commercially viable autonomous vehicle.