Design and construction of a motorised wooden mortar and pestle system for grain pounding in homes
Abstract
The following is a documentation of the final year project as per requisite for the award of Bachelors of Science in Mechanical Engineering degree. The project focuses on design and construction of a motorised wooden mortar and pestle system for groundnut pounding in homes. Food milling has been a very important activity over years where by people used to mill food on rocks in the early ages. Later, people started using coals of fire and stones to do wood carving to make wooden mortar and pestle tools for milling food. This was more efficient and safer since the rocks contain some harmful elements when food milled from there is consumed. Advancements in technology led to the evolution of machines that can mill food faster since the wooden mortar and pestle tools were slower and caused physical strain on users. However, the milling blades keep wearing off over time and the chips keep falling in food and this poses a big threat to human health when such food is consumed. In response to these challenges, a system has been made that uses an electric motor to power a mechanism that pounds groundnuts using the traditional wooden mortar and pestle tools. The motor runs a pulley system which reduces the speed of the motor to a controllable speed at the output pulley. The output pulley is connected to a crank plate by a solid shaft and subsequently, the rotational speed of the crank plate is the same as that of the output pulley. On the crank plate is an off-centre shaft which is perpendicular to the plate. A linkage was fitted with this shaft on its top and the pestle at the bottom end, ensuring that all the joints on the links were pin-connected and the pestle is guided to move only in the vertical direction. The off-centre shaft, linkage and the pestle thus convert the rotary motion of the crank plate to reciprocating motion of the pestle to pound the groundnuts in the mortar. The loading capacity of the mortar used is 1kg of groundnuts and the average calculated pounding rate of the pestle was 3.3 times per second. The average measured time for pounding this quantity of groundnuts to the minimum grade for human consumption was 5.5 minutes. The average loading and unloading time was 20 seconds each. The machine consumes energy of 0.37kWh when turned on for an hour. For low voltage single phase domestic power consumption at 240V, the maximum UMEME tariffs are at 797.3 shs/kWh. This means that the machine consumes power worth 295.001 Ugandan Shillings when run for an hour. In conclusion, this project successfully developed a cost-effective and efficient motorised system for pounding groundnuts through careful design, optimization, and collaboration. The resulting product offers a balance between energy savings, affordability, and functionality. However, opportunities remain for further refinement. The fabricated system should integrate a stirring mechanism for more efficient pounding of the contents. The design pounding rate should also be improved through careful design processes to produce a faster machine thus improving the production capacity of the system. Additionally, product diversification with variations in sizes, capacities, and features will cater to diverse consumer and business needs, ensuring the product remains versatile and in-demand in the marketplace.