I.M.Bashiri , Zubairu Mustafa  and Gambo Anthony
Department of Agricultural Engineering, Kaduna Polytechnic, Kaduna
E -mail;

The production of Acha (Digitaria Spp), a very important nitriceous crop in Nigeria is still very low compared to its demand. To achieve increased production, indigenous engineering initiative and effort to design and develop machines to mechanize all phases of acha production is very necessary. It is in line with this that acha hulling machine was designed and constructed. The machine has a hulling efficiency of 81% and through put capacity of 32kg/h. the above results can increase with further improvement of the machine.

Keywords: Development, acha, hulling, machine.

Acha (Digitaira spp) is a cereal crop from the grass family. It is probably one of the oldest African cereal. For thousands of years, West Africans have cultivated it across the dry savannas, in fact, it was their major food even though few other people have ever heard of it. This crop still remains important in areas scattered from cape Verde to Lake Chad, Mali, Burkina Faso, Guinea and Nigeria.(Philip and Itodo,2006)
Despite its ancient heritage and widespread, importance, knowledge of acha’s evolution, origin distribution and genetic diversity remains scanty even within West Africa itself.

Part of the reasons for the neglect is that the plant has been misunderstood by scientist. This neglect made it to be considered as a lost crop of Africa. (Vietna meyer et al 1996). However, acha is being gradually rediscovered and considered for improvement as cultivated species (Ibrahim 2001, Morales Payan, et al 2002). More and more farmers are now engaged in its production. In the year 2002, a total of 347, 330 hectares of land were devoted to acha production in Africa with Nigeria alone providing almost half of the area (FOASTAT 2003). Acha is grown in various parts of Nigeria, Sierra-Leon, Ghana, Guinea Bissau, Senegal, Togo, Mali, Benin Republic and Cote devoir (Jideani, 1999 Gyang and Wuyep 2005).
Acha is known by different names in various communities in Africa such as Acha in Nigeria, Findi in Senegal, Findo in Gambia, Fonio in Sierra Leon, Founde in Mali, Foni in Burkina Faso Kpendo in Guinea Podgi in Benin Republic, Pom/Polin in Cote’d Ivoire and Hungry rice in English. (Gyang and Wuyep 2005).

In Nigeria,  acha is grown in commercial quantities in some states such as Bauchi, Kaduna Kebbi, Plateau, Nassarawa, Niger, Gombe and FCT with Plateau state being the highest producer  with an estimated production of 20,000 ton per annum (Gyang and Wuyep 2005)

Nutritional value and uses
Acha contains about 7% crude protein that is high in leucine (9.8%) methrionine (5.6%) and valine (5.5%), (Temple and Bassa 1991). It can be made into a numbers of dishes such as porridge and conscious. It is mixed with other flours to make bread, pastries popped and beer brewing. It can also be used as weaning food and it is recommended for diabetes patients by doctors (Jideani 1999).

Production and processing
Acha is usually cultivated on small farm areas using traditional hand tools. It is a small herbaceous annual plant that grows to a height of  30-80 cm. Research shows that farm areas of below 1 hectare are used in its cultivation (Kwon Ndung and Masari 1999, Kuta et al 2003). Its production is generally considered laborious, so also is its harvesting and processing.
The final processing of acha before usage is the hulling which is the separation of the hull
( outer covering) from the grain of a crop  either mechanically or manually by either impact or shearing forces. This aspect of acha processing is the most tedious as it is only manually done by using the mortar and pestle and therefore discourages the farmers from producing it, because they have to pay for hired labour to hull it for.

There are no hulling machines presently in Nigeria even though attempts have been made in their production. An indigenous hulling machine was developed in 1981 by Engr Y. Kwa in Jos, Nigeria. Lack of Government interest made the machine to go unnoticed (Gwom, 1972).
However, hulling machines have been developed and are in use in Bamako and Senegal (Cruz and Prame ,undated).  It is with the view to reducing the drudgery involved in manual hulling of acha and to encourage increased productivity that this machine was developed.

Materials and method

Design Consideration
In a design work like this, the usual thing is make a detailed study of the properties of the crop which will help in the design of the components of the machine   Some of the properties of acha which were considered for this design are the angle of repose used in designing the hopper for easy flow and shape and size for the design of the concave.

The acha grain is really very small, oval shaped with slightly flattened side. Its dimension is length 1.5mm and width is 9mm. (CIRAD 2004). These dimensions were used to determine the clearance between the concave and the cylinder of the hulling unit and also for the selection of the concave screen to only allow the hull to pass while retaining the hulled acha seeds.
Description of the hulling machine
The acha hulling machine consists of the following major units: the feeding unit, the hulling unit, power transmission unit and the frame. Figs 4 and 5 show the constructed machine  and the orthographic views of the machine.

  1. Feeding Unit. The feeding consist of;
  2. Hopper: This holds the acha while it is hulled. It was made of 1.5 mm gauge mild steel sheet trapezoidal shaped to al easy flowing of the materials.
  3. Feeding auger: This is situated at the base chamber.
  1. Hulling Unit: This is where the acha is hulled by the action of the rotating drum against a stationary concave.
  2. The drum or cylinder: The drum is made up of hollow cylindrical pipe of 64mm outside diameter and 340mm long. Six rubber corrugations are line around the cylinder to facilitate the rubbing action for the hulling process.
  3. The concave: The concave is made up of 1.5mm thick iron screen. The screen is curved to take the shape of a hulling chamber and permit the hull to drop freely through the screen.
  4. Driving Unit: The driving unit is consisting of the prime mover which is either an electric motor or petrol/diesel engine. It also has the pulleys belt and bearings.
  5. The Frame: This is made of angle iron cut and welded together to form a rigid structure upon which all the components are assembled.


Design parameters
Many of the crop properties are normally taken into consideration in the design of components of the machine for processing. Two properties of the acha were considered as follows.

  1. Size and Shape

Unhulled (paddy) acha is a small grain which is oval in shape with a slightly flattened side. It is about 1.5mm in length and 0.9mm in width (CIRAD 2004) Fig1


                                               Fig.1 An Acha seed
2 Angle of repose
The angle of repose of a heap quantity of acha was determined in the laboratory and was found to be 23o

Design of components

  1. Hopper: The cone is in the form of truncated square cone. Fig.2


                                                          2 50mm
                                            Fig. 2 Hopper design
Determine the volume of hopper  capacity
Using hl 1/3 base area x height
Where v = volume
H = height of hopper = 0.87m
W = width of the top of copper 0.4m
Volume = 1/3 (40 x 40 x 0.087)
= 0.0139m3
Bulk density of acha = 500kg/m3
:. Capacity of hopper  500 x 0.0139 = 6.96kg

b) The drive
The belt transmits power from the prime mover to the huller cylinder drum with the aid of two pulleys and a belt. The size and speed of pulleys including forces acting on the belt need to be carefully analyzed from proper belt and pulley selection. Fig.3


                                                                                           Cylinder pulley
motor pulley                                                                     
Figure.3  Belt – pulley arrangement


Determination of cylinder pulley diameter from
Dc =    Dm x Nm     ………………………………1
Where Dc        =          cylinder pulley diameter
Dm      =          Motor pulley diameter = 60
Nm      =          Motor pulley speed = 1 460rpm
Nc        =          cylinder pulley speed = 452rpm
:. Dc     =          190mm

Determination of centre distance (C) between the two pulleys
From the equation

C = Dm + Dc + Dm      (Nash 1982, Jansen 1957, Quayle 1986) …………2
:. C 185mm
Belt Selection
Theoretical length of the belt (L) is given as
L = 2C + 1.57 (DC+DM   +    DC – DM )   ………………………………………..3
                               2                        4C
With c = 185mm, Dc = 190mm,  DM = 6.0mm
:.    L = 496mm.
Arc of contact made by the belt on pulley θp is given as θP  =  Rc – Rm       …………….4
Where θp = arc of contact
Rm = Radius of motor pulley
Rc = Radius of cylinder pulley
C = centre distance of pulleys
:. Θp = 440
Angle of contact of belt on motor pulley (θm)


is given by θm = 180 – 2 θp   ……………………………5
θm = 92o
angle of contact on cylinder pulley
θc is given as
θc = 180 + 2θp
θc = 2680


Torsional Moment (Mt) = 9556 x power (kN)    (Hall et al 1982) ………….6
Where power (p) = 0.746kw
Speed (N) =     452rpm
:. Mt = 32 NM.


For belt derive Mt = (TI – T2) R Hana and Stephen 1984)   …………………7
Where  Mt       =          torsional moment
TI         =          Tension on the tight side of belt
T2         =          Tension on the slack side
R          =          Radius of motor pulley


For V– belts, TI/T2 = 5   ……………………………………………8
:. 5 T2 = TI
substituting   TI  = 5T2 into Mt = (TI – T2)R
T2         =          267N
TI         =          1333N

c) Power transmission shaft
Power design consists primarily of the determination of the correct diameter to ensure satisfactory strength and rigidity when the shaft is transmitting power under various operating and loading conditions and so the shaft was designed from the stand point of strength and rigidity
The shaft subjected to both bending and torsional loads.
The maximum bending moment was calculated to be 24.13Nm
According to Harper (1980) shirgley (1980) and Hana and Stephen (1980), the required diameter of shaft from ASME load equation is given as


D3 = 16 πss √(kbmb)2 + ktmt)2                     ………………………………………………….9
D         =          diameter of shaft
Ss         =          allowable stress 40 x 106 Nm
Kb       =          combine shock and fatigue applied to bending moment

    1. to 2.0 for minor shocks.

Kt        =          combine shock and fatigue applied to torsional moments

    1. to 2.0 for minor shocks.

           Mb        =          maximum bending moments = 24.13Nm
            Mt        =          Maximum torsional moment = 2.1
           Diameter of shape D = 20mm
Considering a factor of safety of 1.6
Recommended shaft diameter = 32mm

d) Power requirement
The power required to derive the drum is given by


Pd = Fv =    mv3     ……………………………………………………….10
Pd = Power required
M = Mass of hulling drum 3.2kg
R. = radius of shaft = 0.032m
v. = velocity 5.03ms
Pd = 2.5 kw (3.4 hp)


Figure 4: The constructed acha huller

 Figure 5: Orthorgraphic drawing of the huller               

Performance evaluation
The machine as shown in Fig.4 was evaluated using the following indicators;

  1. Hulling efficiency (%) this is the measure of the effectiveness of the machine in the removal of the hull.
  2. Quantity of the product within a certain period of time.

Test procedure
Two kilogram of the acha was measured and put into the hopper and the machine was operated until the hopper was empty. This was repeated four other times and the result was recorded as in table 1.




Table 1 Test results
       Weight of    Weight of         Weight of        Weight of        Time      Hulling     through put
Sample    Acha (Ws)  hulled acha    hull removed    un hulled acha   taken     efficiency   kg/h
                                      (Wha)             (Wh)                 (Wuh)             min              Eh
          1           2                    1.60             0.25                     .15             3.0            80             32
2            2                    1.64             0.22                     .14             2.5            82             32.8
3            2                    1.65             0.23                     .12             2.8            83             37
4            2                    1160            0.25                     .15             2.6            89             32
5            2                    1.63             0.23                     .14             2.5            82             32.6
Total             10                  8.12            1.18                      0.7             13.4          707           2.4
Mean             2                    1.62            0.24                      0.14           2.68          81.4          32.48
Hulling Efficiency   =   Wh    x 100%  …………………… 11   

Where  Wh =Weight of Hulled acha
              Ws = Weight ofsample

Throughput Capacity (Kg/h)       =  Ws  …………………..12 
                   Where Ws = Weight of sample                    
                                T = Time in hours                       

The result of the preliminary test showed that the machine has a hulling efficiency
Of 81% meaning that 19% of the product is un-hulled which is on the high side considering the fact that the acha should be hulled as completely as possible or only a very small percentage should remain un-hulled. This result showed as good promise of an efficient hulling machine.
Further improvement on the machine is necessary after which it should be properly evaluated. Parameters to be evaluated will include different speeds of the rotor, different varieties of Acha, different feed rates.

Acha has the potential of providing enough food for the increasing population of the poor people in Nigeria. It‘s low yield due to laborous and unimproved husbandry practices is responsible for decline in its production.

Acha production in Nigeria has to be stimulated by initiating research activities towards addressing the existing biological, agronomic and mechanization constraints that currently discourage its increased production. Therefore, with the encouraging results obtained from the designed huller, and by commercializing the machine, acha production will be boosted and its future looks bright.

CIRAD.(2004) .African Cereal Crop. French AgriculturalResearchCentre for International Development
Cruz, J.F and D. Drame (undated) http// fonio.

FAOSTAT. 2003 Database . Food and Agricultural Organizations’

Gyand J.D.ND E.O.Wuyep (2005) Acha; The grain of life . A biannual Publication   of the Raw
Materials Research and Development Council .Vol.6 No.1:39-41

Hall, W. C., Ferral. A.W.,Ripper, A.L. (1986), Encyclopedia of food Engineering 2nd edition ,  AVI
Publishing Coy, Inc.WestPort.

Hanna,J. and R.C.Stephen (1972): Mechanics of Machines. Edward Arnold Publ Ltd pp371-374

Ibrahim, A.(2001). Hungary Rice (ACHA) ; Aneglected Cereal Crop. NAQAS Newsletter. Vol.1No4:4-5
Jideani, I.A. (1999). Traditional and possible Technological uses of Digitaria exilis (acha) and Digitaria ibrua (iburu). A Review. Plant Food for Human Nutrition. Kluwer Academic Puplishers .Printed in the Netherlands 00:1-13
Kwo-Ndung, E.H. and S.H.Misari (1999). Overview of Research and Development of Fonio   (Digitaria Exilis Kipps Stapf) and Prospects for Genetic Improvement in Nigeria. GSn Pupl., Nigeria,pp. 71-76.

Morales-Payan,J.P., Ortis, J.R.; Cicero, J. and Taveras, F. (2002). Digitaria exilis as a crop in the Dominican Replublic.Suplementt. Trend in New Crops and New Uses. J. Janik and A.Whipkey (eds) ASHS Press, Alendra, VA. Pp. S1-S2

Nash,W,A,(1982). Strength of Material, 2nd ed. New York:Schaum;s Outlines Series.McGraw-Hill Book Coy.

National Research Council (1996). Lost Crops of Africa . Volume 1. Grain National Research Counncil. National Accademic Press Washington,DC pp59-775.

Qayle,J.P. (1986):.KEMPS engineering Year Book 91ST ed,New York: Morgan –Grampian Book Puplishing Coy Ltd .

Shirgley, J.E. (1972): Mechanical Engineering Design. (2nd Ed). McGraw Hill Book Co.   NewYork


Temple,V.J. and Bassa, J.D. (1991): Proximate Chemical Composition of Acha (Digitaria exiklis) grain   J. SC. Food Agr.56-561-564.

Vietnameyer, N.D., Borlaugh, N.E., Axtell, J., Burton, G.W., Harlan, J.R., Rachie, K.O. (1996). Fonio (Acha).In: Lost Crops of Africa. Vol. 1. Grain New York: BOSTID Puplication, National Academic Press