Thesis (M.Eng.) - Asian Institute of Technology, 1994

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering.

The performance of a power tiller locally manufactured and commonly used by farmers in Thailand was evaluated. The power tiller without a PTO shaft is commonly used in Thailand and this type of power tiller was used for testing. It has two forward and one reverse speeds and it is equipped with a 6.3 kW Yanmar (TFL 85) diesel engine. The power transmission of this power tiller from the engine to the rotary shaft and wheel axle consists of 3 sets of V-belts and gear trains in the gear box. Necessary fabrications were done to fix two torque-meters directly with engine and rotary unit and two drum brakes (prony brakes) on both sides of the wheel axle. The evaluation· dealt with the measurements of the engine power, rotary power, and axle power by loading, at wheel axle and rotary shaft, in the laboratory. Varying parameters like axle loading, rotary shaft loading, center distance between pulleys (belt sag), the number of belts, and the size of pulley, a maximum of 4.24 kW of power was recorded at no external load on wheel axle. In this case the transmission efficiency was about 88%. It was observed that the power transmission by the V-belt was a function of belt tension (belt sag) and slip. It was found to be a function of diameter of the pulley transmitting power from intermediate shaft to rotary shaft. A combination of 7" and 3" pulleys gave more transmitting efficiency with the belt sag of 21 · mm/m of center distance.