An Innovation in Australia A long row to hoe The Howard Rotavator In 1912, 16-year-old Cliff Howard had an idea that would change the way small farms were cultivated. To make hoeing more efficient, Howard introduced power to the hoe’s blades, so that they would dig the earth and help push the hoe forward at the same time. All the farmer had to do was steer.
Howard Rotavator It took ten years for Howard’s first Rotavator to be perfected. At their sales peak in 1970, 100 000 a year were exported to 120 countries.
A Problem When rotary tillers are used in very grassy paddy fields, in which soils are soft and grass difficult to cut, grass and straw twists on their rotary axles and rotary blades thus preventing rotation
Grassy paddy field Straw with thick weeds after harvesting
Grasses twist on rotary axles and rotary blades
Research Aims Overcome the above problem, preventing grass and straw to twist on rotary blades Evaluate grass-removing performance of rotary blades with grass-removing angles Calculate magnitude of grass-removing angles Help design rotary blades with better grass- removing performance
Rotary Blade When a rotary blade is cutting into soil, the edge of the blade can be considered as a cutting edge At any point of the edge curve, a tangential line can be used to represent the cutting edge of that point
Analysis of is the angle between the velocity and the normal line of edge curve The absolute velocity is the resultant of linear velocity r and forward velocity u can be divided into s and d
Application For a particular type of rotary blade (e.g. Archimedes spiral), one needs to calculate the blade’s static s and dynamic d slide cutting angles and to evaluate the grass removing performance of the blade
Archimedes’ Spiral r = r 0 + K r 0 = 135 mm, r max = 228 mm, 0≤ ≤27º = 0.47 rad K = 3.44 mm / deg = 197.35 mm / rad, R = 245 mm
Calculation of slide-cutting angles for Archimedes’ spiral
From the graph At the shank part of rotary blade, is large and the dynamic slide-cutting angle d is small At the shank of the rotary blade there is a greater propensity for grass and straw to twist than at the tip Static slide-cutting angle s at the shank should therefore be increased
Sine-index Spiral For sine-index spiral, s could be greater at shank part than at tip part of the blade Rotary blades would have better grass- removing performance
Comparison of sine-index with Archimedes’ r (mm) dd
Conclusion In paddy fields, grass and straw twist easily on rotary axles and rotary blades Dynamic slide-cutting angle d is always smaller than the static slide-cutting angle s Static slide-cutting angle s should be greater at the shank part than at the tip part Sine-index spiral, Archimedes’ spiral and straight line can be used at different situations