The Sowing Machine is an implement that plants grain seeds in a row, evenly spaced. There are two seeders that will be discussed: the wheel sowing machine and the punch seeder. There are advantages and disadvantages of each. There will be a discussion at the end on the merits of each. Both, of these machines, have in common, the ability to suck and hold one seed and plant it at a precise spacing and an accurate depth.
The Sowing Wheel is shown in the figure below, moving to the left. A large spring harrow tine is used to clear the path of trash, straw and debris. See Figure 2.
- The row needs to be cleared of trash and debris. A spring harrow tine scratches the ground and pushes aside the surface debris and straw. This is done so that the following colter will not hair-pin straw into the seed row.
2 The colter is a thin round disk that cuts the roots and straw down to the depth of the seed row. The outer edge would be sharp and serrated. The colter could be made to castor, to facilitate shallow turns; however, the overall design is for working in a straight line. The colter could have a collar that would roll on the surface for depth control.
3 The plow is used to widen the seed path and to hold the path open to protect the seed being carried on the seed wheel. The colter is thin, perhaps only an eighth of an inch, and the plow widens the path to three eights of an inch. Normally a curved shank or plow will catch and carry trash; but, this plow wraps around the colter so that the colter would clear the trash. The trailing edge of the plow could be used to inject a water/fertilizer mix into the soil. A pulsed piston pump could be used to accurately meter the water between where the seeds will be positioned to keep the fertilizer deep; but, avoiding contact with the seed.
4 The Runner / Shoe is welded to the side of the plow and acts as depth control and somewhat protects the integrity of the seed trench made by the plow. It would extend about 0.75” from the plow. The runner / shoe would act much like a pressure foot on a sewing machine to hold the cloth in place as the needle pierces the cloth. In this case the soil is being held firmly in place.
5 The Seeder Wheel is the main part of the sowing machine. The diagram shows 50 hollow spokes that go to the outer rim of the wheel for 2” spacing, giving a circumference of 100” and a diameter of 31.83”. The rim is only 5/16 “, to nicely fit in the 3/8 inch path that the plow made. The hole in the rim is the same diameter as the seed in question with a center pedestal that looks much like a valve stem on a car tire. The idea is to let enough air to suck up a seed and hold; but, not so big as to have the seed get stuck in the hole.
Picture the wheel rotating CCW. Starting at the 4:30 position, the rim of the wheel is entering the seed box. The seed-box is made with tight tolerance to fit tightly around the wheel, so that seed does not leak out. Vacuum is applied to the spoke, so a single seed is sucked onto the hole and is held firmly onto the edge of the wheel where it exits the seed box at 2:00 o’clock through an opening that is slightly bigger than a seed. The seed is held tightly to the edge of the wheel, all the way around to the bottom of the wheel and the vacuum changes to pressure and the seed is blown off the rim and pushed into the bottom the narrow trench made by the plow. The seed wheel could have a collar on it to ride on the surface of the soil for depth control.
A commutator in the hub of the wheel would be used to pressurize the tubes from 6:00 to 4:30 o’clock to blow off the seed at 6:00 and to clear any debris from the rim’s hole from 6:00 to 4:30 position. All spokes from 4:30, all the way around counter clockwise to 6:00 would have vacuum applied to hold the seed.
6 The seed box fits tight enough around the wheel so that seed grain will not leak out, yet not so tight as to bind. The very bottom of the seed-box has a scraper that keeps the wheel clean of mud and debris and may the occasional seed that is not ejected from the wheel. The seed box is kept about half full of gain – just enough so that there is enough seed for all holes on wheel can capture a seed, yet not so much that the seed is rubbed off. Vacuum is applied to the spokes from the 4:30 position, around the top, all the way to the 6:00 position in which it changes to pressure to force the seed off the rim, yet firmly planted in the seed trench.
7 The packer wheel is shown in Fig 1 packing to the bottom of the seed bed. It would practically be set somewhat higher than this; perhaps to just below the ground’s surface. The packer is also used to control the depth of seeding.
8 The fender wraps around the wheel, much like a fender on a bicycle, but; with a much tighter fit to protect the seed clinging to the rim as it makes its way all the way around.
This sowing machine with the wheel, has the advantage of being able to travel quite fast, but it has the disadvantage of preset seed distance, and much soil disturbance. The punch seeder, that will be discussed next, has very little soil disturbance, and better trash clearance, but; it would have a slower travel speed.
Punch Seeder: Both the punch seeder and the wheel seeder are predicated on the ability to suck up a single seed with a hollow tube and to hold it until it is pressed into the ground at a precise depth. The wheel seeder has many such suction tubes, whereas the punch seeder has only one. See Figure 3 below.
To create this J shape, a cam wheel is used to produce the vertical and horizontal displacement. Let’s start with the vertical displacement. Each cycle will be one revolution of the cam wheel which will be broken into 10° increments, 1 to 36 as shown as the horizontal axis in Figure 5. It is assumed that the punch must be lifted over the edge of the seed box of 1 inch. The ground level is referenced as zero of the vertical axis shown in inches. The seed depth is set to 2 inches. The cycle starts at 1 with the tip of the punch in the seed box, sucking up a seed. At 9 the tip of the punch is lifted over the seed box and hen proceeds down, to ground level at 14. At 18 the punch is at its lowest level, two inches into the ground. Vacuum in the tube is switched to pressure to force the seed off the punch. Air pressure continues at 22 as the tip surfaces and is lifted to its highest point at 27 to clear the seed wall. Air pressure is switched to vacuum as the tip of the punch goes into the seed box to suck up and load another seed at 36.
The vertical cam on a 10”cam wheel is shown in Figure 6 with the cog being at the top, being pressed downward onto the cam with a spring. The cam wheel would rotate CCW.
The horizontal displacement cam will move the punch tip forward into the seed box, + 1”, and then back to the wall of the seed box which is referenced as 0, at 9. The punch enters the soil at 13 and the horizontal speed of the tip is set to match the ground speed of the seeder. Let’s assume that the seed spacing is 2 inches; therefore, we need to complete a cycle for every 2” of ground covered, — 2” per cycle. If the punch is in the ground for 90° (13 to 22) of the cycle, that would equate to a distance traveled of 0.5 “. At 13, the punch is 1” behind the seed box wall. Over the next 90°, the punch should be pulled back a half an inch to 1.5” behind the seed box wall in a linear manner to match the ground speed. The horizontal displacement cam would look like Figure 7.
From 22 to 36 the punch is pushed forward, back into the seed box for another load.
On a 10” wheel the horizontal cam would look like Figure 8.
The x or horizontal axis is at ground level, and the y or vertical axis is the trailing edge of the seed box. The tip starts to the left (-1,0) inside the seed box and it is shown much to deep at ground level; it should be much higher. It then travels to the right, over the edge of the seed box (1,0) until it is behind the seed box over the ground. (1, 0.5). It enters the ground (1,0) and then the tip matches the ground speed as it is inserted 2” and extracted (1.7, 0.25). It is then pulled back quickly to the edge of the seed bin and back into the seed bin to load up another seed.
Another cam, on the same cam wheel is used to switch the vacuum to pressure in the tube. Pressure, 15 to 26; otherwise vacuum as shown in Figure 10 and 11.
. A hollow tube slide valve would apply pressure or vacuum to the punch. Vacuum to suck and hold the seed on the tip of the punch, and pressure to release and plant the seed. OR the cam could drive a piston in a cylinder to supply the vacuum, (when pulling back) or pressure (when driven forward) as controlled by the cam. The tube travels in a half circular arc; into the seed-box with suction applied to the hollow to suck a seed onto its tip. The seed and tip then travel in a circular arc, out of the seed box and onto the seed path and placed 2” below the surface, as air pressure is applied to the hollow tube to gently release the seed.
Whether a seed wheel or a punch; the tip of the tube where the seed is held must be designed carefully to allow as much surface area as possible for the seed to stick, yet, not so big as to get stuck in the hole.
The tip of the punch seeder is shown in Figure 12 with the seed stuck at the top of the tip. The barrel of the punch is hollow to have a vacuum applied to suck up a seed, or to have air pressure applied to remove the seed. The diameter of the barrel is close to the diameter of the seed. Oblong seeds would have the barrel the same size as the longest dimension of the seed. The pedestal in the middle is to support the seed, as it is being pressed into the ground so as to not get pushed into the barrel. The pedestal has a hole in the center and is hollow to allow for suction, and pressure to be applied in the center.
The punch seeder would have a ski, or a runner, or a shoe; much like on a sewing machine to partially clear the seed row of debris, but also to hold the soil firm for the punch and to control the seed depth.
How fast could we seed? Let’s assume the seed separation is 2 inches. I would think the limiting function would be the loading and securing the seed on the suction tube and then doing the semi-circular path to get the seed placed. Consider a valve in a car motor that goes up and down much like our seed punch. At 2400 RPM would be 40 times a second; there is more distance to cover and we need to allow for the seed to be secured and some experimentation would be required, but let’s say 10 cycles per second would be obtainable. Another example would be a sewing machine, certainly it can do 10 stitches in a second. Ten seconds at 2” would result in 20 inches per sec. or 1200 inches per minute, or 100 ft per min. or 6000 ft per hour. – Just over one mph. This might seem slow, but then again if this is a machine that goes 24/7 it could get the seeding done in a timely manner. The sowing wheel could potentially go much faster, but with more soil disturbance.
The punch seeder has less soil disturbance and better trash clearance, but it is slower.
The punch seeder has a more complicated motor driving the cam wheel to match the ground speed, whereas the sowing wheel, automatically rolls to the ground speed. The punch seeder has more flexibility in seed spacing, and is easier to change seed size.
Both seeders have the hollow tube going into a seed box to suck and hold a single seed; and hold it until it can be placed into the ground.