Engine Reaction Torque Sensing on Walking-type Power Weeder

Abstract

Self-propelled small farm implements (rotavator, weeder, ridger, etc.) can play important roles in small-scale farming in developing countries, and their efficacy, or quality of operation should be commensurate with power consumption. Nonetheless, measurement of the power of small machines is difficult due to limited space for mounting torque-sensing devices. In this study, a simple and direct sensing of engine reaction torque was devised for evaluating the power consumption of a walking-type power weeder in paddy fields without the need for installing slip rings. The fitting between the housing of engine and the main body of the weeder was modified allowing the engine to rotate freely around its own center shaft, and a cantilever load cell was fixed between them to convert the force into engine reaction torque. Dynamic calibration was carried out in the laboratory to determine the relation between the engine reaction torque measured and the rotor shaft torque applied stepwise; the relation was linear with a coefficient of determination (R-square) of 0.98. Random and incessant setting of the rotor shaft torque resulted in a root-mean-squared relative error of 4.2% of estimation based on the calibrated relation. By multiplying the rotational speed with the rotor shaft torque, the power requirement of the weeder was accurately and continuously recorded in actual wet field conditions.