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THRESHING TESTS

Near the beginning of the program of thresher development, the following tests were performed:

1. In February 1974 the first prototype pedal thresher was tried out. Drum diameter 400mm, driver pulley 630mm diameter, driven pulley 80mm diameter, belt drive. Drum speed 525 rev/minute. Beater velocity 10 metres/second. The writer pedalled while 2 others fed heads of sorghum to the beater-stator interface. The particular thresher utilised wooden bearings throughout, and , under zero load, static torque requirement at the pedals was 9 Newton-metres (that gives 54 watts energy loss while pedalling at 60 rev/minute - a bit unacceptable). After 20 minutes continuous threshing, the collected grain was winnowed and weighed at 11.5 kg. The pedaller subjectively felt his endurance at that (unknown) power output would have been 30 minutes maximum.
2. In the same week, some sorghum heads of 18% moisture content were placed in a jute sack and beaten by the writer to his endurance time - 10 minutes in this case. It was visually estimated that only 50% of the grain had been threshed, and after winnowing the sample was weighed at 5.2 kg.
3. On the same day, some sorghum heads of 13% moisture content were placed in a sack and beaten as before with a wooden stick. 5 minutes of threshing produced 3.16 kg of clean grain, with an estimated 0.15 kg unthreshed. Endurance time again 10 minutes, and same operative (the writer).
4. Again on the same day, approximately 4 kg of cowpeas were hand threshed for 5minutes. The work was extremely light compared with the previous 2 tests, and on inspection the cowpeas were entirely threshed.
5. Shemsanga (1975) conducted the following brief test for the writer - a 3 horsepower (2.25 kiloWatt) engine-driven rasp-bar thresher was used on the University Farm for threshing sorghum heads of low moisture content and moderate yield. Over 5 minutes, 15.63 kg of uncleaned sorghum was threshed, for a petrol consumption of 20 millilitres.

ANALYSIS OF THRESHING TESTS

From the data presented above, the following table can be derived:

TABLE I - Analysis of Sorghum Threshing Tests

Thus if one neglects the power input of the people feeding heads to the thresher (!), and if one assumes the use of an efficient power transmission (with effectively zero power loss), then it appears that for sorghum the use of a pedal thresher multiplies labor productivity by 1.9 to 2.2 over hand threshing. That compares with Islam's factor of 2.3 for the threshing of rice.

For Test # 4 (cowpeas) , power consumption was too low to be estimated (and anyway no comparable machine threshing was performed).

For Test #5, thresher output was 187.6 kg / hour for petrol input of 0.24 litre/hour. Assume calorific value of 10.5 kWh / litre, and engine thermodynamic efficiency of 15% to 25%. Thus specific energy requirement appears to be 2.01 - 3.36 kWh/tonne . That ties in with the calculated value of 3.1 - 3.3 kWh/tonne for pedal threshing as per Test #1 (Table I above).

Thus a pedal thresher appears to multiply labor productivity by a gross factor of 2.05 when compared with hand threshing, and a net factor of 1.37 if one considers a case with 4 pedallers plus 2 persons hand-feeding.