Assumptions: The assumptions made in the design of the rotary weeder are presented in terms of field conditions, machine capacity and energy requirement required to power it. The machine is to be powered by a 48 volt 1140 watt motor which is operated by 48 volt rechargeable dry cell battery. Belt and Pulley arrangement shall be employed for transmission of power. Motor speed is 1400 rpm, Number of teeth on Spoket = 14, Number of teeth on Spoket of common shaft = 14x2 = 28, Number of teeth on Spoket of rotary shaft= 28, Number of teeth on Spoket of wheel shaft= 48, Rotary shaft speed = 350 rpm, wheel shaft speed = 205 rpm, maximum soil resistance value = 1.05 kgf/cm2, coefficient of friction = 0.1, efficiency of transmission system = 82%. Transmission of power.
Design Process: Bainer et al. (1978) asserted that in designing row-crop weed control equipment, the age of the weed must be taken into consideration. In the early stages of crop growth, implements such as a rotary hoe, the spring tine and spike arrows can be operated directly over the rows to uproot small weeds from established crops. Hunt (1983) asserted that, in the design of a rotary hoe, there must be uniform and adequate penetration of the tools. This, he obtained by adding weights to the rotary hoe and to spike tooth harrow. In the design of a manually operated machine, the power supplied by a man working continuously should be taken into consideration. Human beings as power units are limited to less than 0.1 kW output. This suggests that the weight of the implement must be considered and made to bear in the selection of the materials for construction. Pd = {(sr x d x w v) / 75} x hp.
Where, Sr = soil resistance, kgf/cm2;
d = depth of cut, 3 cm;
w = effective width of cut, 12x3=36 cm;
v = linear velocity of the tine at the point of contact with the soil, 1cm;
Chain and shaft selection: The chain, spoket and shaft selection was based on Agricultural Machinery Management Data.
Machine Description: The weeder consists of the following components; a 48 volt 1140 watt motor which is operated by a 48-volt rechargeable dry cell battery, two ground wheels, tool assembly, frame and handle. The power to the rotary hoe and the pushed wheel is supplied from the motor through chain and spoke arrangement from a neutral shaft. The weeding tines on a cylindrical disc were arranged radially at equidistance of 20mm along the disc circumference. Each tine was made of a flat steel bar of 10 mm width and has a 900 arc of 10mm. The rotary power weeder is to be powered by a 48 volt 1140 watt motor which is operated by 48 volt rechargeable dry cell battery. Chain and spoket arrangement was adopted for transmission of power. The maximum rating of the 48 volt 1140 watt motor was 1400 rpm fixed with a spoket diameter of 50 mm with 14 no teeth on the shaft carrying the rotary tines. The various components of the machine were constructed while other standard components, such as prime mover and transmission elements were sourced locally and the parts were assembled at the fabrication workshop of the Farm Machinery and Post-harvest Process Engineering Division, BARI. The isometric view and the front view of the rotary weeder.
Performance Evaluation and Experimental Analysis: The performance evaluation of the constructed rotary power weeder will conduct on the experimental field of Farm Machinery and Postharvest Process Engineering Division, BARI. The performance evaluations will conduct to investigate the effect of weed density on the performance of four weeding tools. Prior to each weeding schedule, weed density in each experimental unit was determined by laying-out a squared grid (0.3m x 0.3m) in the plot and weeds in the grid were counted. Three such determinations were made for each experimental unit.
Experimental Factors: Experimental factors used in the field evaluation of the constructed rotary power weeder were the same speed in three blocks. The weeding performance will compare with the BARI manual weeder and traditional weeding method.