This study was done to modify the existing rocker sprayer. Manually operated lever was replaced with an electric motor and the speed of the motor was regulated by a voltage regulator. For determining the power requirement, the speed of the manually operated sprayer was regulated by subjects’ analysis and was found to work with an average speed of 74 rpm of the piston movement. Modification was done to get the same boom length of the sprayer. The power requirement of the sprayer was determined as 0.016 hp, but 0.25 hp motor was used due to market’s unavailability. A model of the slider crank mechanism was developed to study the effect of connecting rod length, crank angle and rpm on the piston displacement and the linear velocity for the modification of the rocker sprayer. It was found that, the piston displacement and the velocity decreases with an increase in the length of the connecting rod and vice versa. Piston linear velocity was found to be maximum at two crank angles in the range of 90-120° and 260-280°. The weight of the implement was about 4.75 kg. The sufficient pressure of 80-90 psi was obtained for the purpose of spraying, as found in the existing manually operated sprayer. The slider-crank mechanism is useful for the development of the power operated sprayer and for other agricultural machineries.