Jump to Content

< back

Pulas Yowat

Project title:

Design and development of a prototype slashing machine for plantations in developing countries.

Brief description of project:

Despite the present vast exploration of raw minerals in Papua New Guinea, it is still predominantly an agricultural country with 80 per cent of the population sustaining their livelihood through it. This is by cultivation of food crops and cash crops as coffee, tea, cocoa, rubber and copra. Apart from gold and copper, agriculture including forestry is the country's largest exporter representing over 35 per cent of the total earning.

Most of the cultivation are in cash crop plantations. The cocoa and coconut plantations are mostly located on the coastal and island areas of Papua New Guinea while the tea and coffee are in the highlands. Since the introduction of commercial plantations in Papua New Guinea, very little has been done to improve the slashing methods. To this date, the slashing of the weed regrowth in the plantations is still dine manually. Although herbicides are available, the cost is still beyond the reach of most small holdings. With the slashing of the plant regrowth as the most frequent activity in the plantations, a Prototype Portable Slasher was designed and developed to assist with this task. The development of this machine was aimed at increasing the overall efficiency of the slashing process in the cash crop plantations.

Before the design and development of the Prototype Portable Slasher, an investigation of the mechanical properties of common plantation grasses in Papua New Guinea was conducted. These mechanical properties of grass stems in Papua New Guinea were gathered using a Stem Impact Cutting Rig designed and built at the University of South Australia. The cutting information from the plant stems was analysed and then used as a basis for the design of the Prototype Portable Slasher. The Prototype Portable Slasher was then designed and built at the School of Manufacturing and Mechanical Engineering, University of South Australia. The machine was tested and evaluated at the Papua New Guinea University of Technology, Lae.

A laboratory and field tests were conducted during the preliminary trials on the Prototype Portable Slasher. Modifications were done to the portable slasher and its components to rectify problems encountered in the trials. These modifications include the selection of a new 24 cc engine and the usage of aluminium engine holding frame. Consequently, the overall weight of the engine assembly is 3.6 kg which has been reduced by almost fifty per cent. Furthermore, this has also significantly reduced the strain on the operators and has eliminated slippage of the strap plug. In addition, the extension spring was modified with reduction in the free length to 306 mm and also the number of coils reduced from 176 to 136. This resulted in constant spring tension to support the weight of the engine assembly.

The above modification were made as the result of several design problems encountered during the preliminary trials. The laboratory tests detected a major problem with the fabric strap assembly due to the partial stitching of the strap socket. This problem further contributed to the slippage of the strap plug because the strap assembly was not vertically aligned with the operator's waist. Likewise, the fabric strap assembly was not able to fully support the machine when it was attached to the operator. The strain of the back of the operator was a main problem observed during the trials. This was due to the weight of the engine assembly. These situations were considered and modifications were done to rectify these problems as discussed earlier.

Apart from this problem, the Prototype Portable Slasher performed very well during the field trials. The Cutting Force per unit area ranged between 3 N/m2 and 7 N/m2 and a Cutting Energy ranged from 3kJ/m2 to 6 kJ/m2. The average fuel consumption per area is 4 ml/m2 and average cutting time of 0.5 minute/m2.
 

top^