| Abstract | In Thailand, government has planned to grow soya bean in 400,000 ha by 2004. Due to increasing shortage of labor, harvesting and threshing of soya bean are time consuming and expensive. At the moment, there is no soya bean combine available for harvesting soya bean crop in Thailand. Therefore, it was planned to develop a soya bean combine harvester in this research. For designing the prototype combine harvester, crop varieties and crop conditions were studied. Four soya bean varieties, promoted by the Thai government. KKU-35, CM-60, SJ-5, and JP-1 were selected to know which variety needed maximum cutting force and uprooting force. Three moisture contents (0.17 to 30% (w.b.), five sizes of stem diameters (3.5 to 9.2 mm) were used during testing. The results showed that the shear force requirement to cut the plant stem increased linearly as the diameter of the stem increased for 3.5 to 9.2 mm. The maximum shearing force for KKU-35, SJ-35, JP-1 and CM-60 varieties were 380.4. 348.2. 324.2 and 259.5 N respectively. The shear strength reduced as the diameter of stem increased. The shearing strength of four soya bean varieties varied from 2.99 to 10.40 N/mm2. The developed threshing unit comprised of a peg-tooth drum of 90 cm lengh and 42 cm diameter. It was tested at four peripheral drum speeds of 15.30, 13.19. 11.00 and 8.80 m/sec and three feed rates of 360, 540 and 720 kg/h. The peg tooth drum at speeds of 600 to 700 rpm (13.2 to 15.4 m/s) and feed rates of 540 to 720 kg (plant)/h was used for developing a threshing unit of a prototype soya bean combine harvester. The output capacity, threshing efficiency, grain damage and grain loss at 700 rpm (15.4 m/s) drum speed and 720 kg(plant)h feed rate were 214.17 kg/h, 99.49%, 0.22% and 0.80% respectively. The grain damage was lower than 1%. The average power requirement was 1.85 kW at the feed rate of 720 kg (plant)/h, 14.34% (w.b.) grain moisture content and at a drum speed of 700 rpm (15.40 m/s). The drum speed of 13.2 to 15.4 m/s for the grain moisture content of 13 to 15% was recommended for the design of soya bean combine harvester. Based on the results above, a soya bean combine harvester was designed and fabricated. The cutter bar and header unit was 1.5 m wide. The peg-tooth cylinder was used. The under-carriage was modified from the under-carriage of 4 ton truck. The machine was powered by a 47.7 kW, four-cylinder diesel engine. The prototype of soya bean combine harvester was tested in the field. Four travelling speeds of 1.80, 2.01, 2.20 and 2.40 km/h were used for testing. The average soya bean grain moisture contents varied from 12.8 to 14.8% (w.b.). The results indicated that the soya bean harvester worked best at a travelling speed of 2.01 km/h. At drum speed of 450 rpm (12.26 m/s), the field capacity and output capacity varied from 0.18 to 0.21 ha/h and 219.26 to 253.04 kg(grain)/h respectively. The average threshing efficiency, grain damage, cleaning efficiency and total losses were 99%. 1.20 to 2.20%, 99% and 8.74 to 10.26% respectively. During field testing at 2.01 km/h forward speed, the engine speed, threshing drum, propeller and header speeds of the machine were 1600, 450, 425 and 210 rpm respectively. The combine harvester gave an average field capacity of 0.21 ha/h, 99% of threshing efficiency, 99% of cleaning efficiency, 1.54% of grain damage and total loss was 9.39% of yield. The power requirement of the machine was 29.94 kW. At the present rate of 4,400 Baht/ha for conventional testing method, a soya bean combine harvester had a break even point at 26 ha/year. For a one year payback period, the harvested area should be 129 ha at a custom hiring rate of 3,125 Baht/ha. |