Design parameters of an acha thresher

Acha (Digitaria exilis) also known as fonio, is a crop with significant food and nutritional value primarily grown in Nigeria and other West Africa countries, where it’s threshing and cleaning processes remains problematic. In an effort to alleviate the problems associated with the traditional method of acha threshing and cleaning which are uneconomical, time-consuming and labour-intensive, an acha threshing machine was designed. The thresher consists of five principal units: feeding, threshing, vibrating/oscillating, cleaning, and power units. The feeding unit is shaped as a trapezoidal hopper with dimensions 400×210 mm (larger rectangle) and 338×210 mm (smaller rectangle), designed to hold 5 kg of acha panicles. The threshing unit features a drum with a diameter of 435 mm and a length of 740 mm, equipped with 44 threshing spikes (20 mm diameter, 92.5 mm length) suitable for acha's fragile grains to minimize damage. The separator has dimensions of 725 mm by 595 mm and uses a sieve with 4 mm holes. The power required for the thresher is 4.0 kW which operates the threshing drum at 10.212 m/s and drives a reciprocating sieve for cleaning the threshed acha. The design is suitable for small-scale farmers involved in acha production in Nigeria, offering a significant increase in labour productivity (8.4 times that of manual threshing). Evaluating the developed acha thresher demonstrated its ability to efficiently thresh acha and separate the chaff/straw from it, with a reduction in grain breakage compared to traditional methods which presents a feasible solution for mechanizing acha threshing.