TESTING

One of the main concerns with the design was the rigidity of the frame that integrates the brush subassembly with the corn head. Using an accurate model and appropriate constraints, finite element analysis (FEA) can be completed. FEA produces multiple graphics with information such as displacement, stress, and safety factor for a user defined loading. For the bracket, the primary area of interest was the displacement. Figure 1 shows the displacement of the frame under loaded conditions. When using 3/16 in mild steel, the max displacement for the load was less than 0.005 in which is more than adequate for this application. A thinner plate may have been acceptable but because total weight is not a concern with the bracket, 3/16 in was selected. Applying a larger load to the frame indicated that 3/16 in would tolerate wear and tear from operation.

Figure 1. Finite element analysis for the brush bracket.

Additional testing was completed post-fabrication to ensure the sorghum leaf harvester functioned properly and met the client’s needs. Initial testing consisted of connecting the system to the tractor and running the system to ensure the brushes, gathering chains, and paddle chains rotated simultaneously. A flowmeter, pressure gauge, and digital tachometer were used to measure the flow rate, pressure, and rotational speed of the brushes, respectively. The flow rate is directly responsible for both the pressure and the rotational speed of the brushes; therefore, the flow rate was increased from 3 gpm to 12.5 gpm to show the relationship between the flow rate and the resulting pressure and brush rotational speed. Figure 2 shows the correlation between the flow rate and rotational speed.

Figure 2. Relationship between flow rate, pressure, and brush rotational speed.

Secondary testing consisted of feeding plant material into the brushes to ensure the brushes are capable of stripping the leaves from the stalks and the paddle chains capable of conveying the leaf material toward the auger. A small number of sorghum plants were available for testing; therefore, other plant material was used to supplement the sorghum during testing. The plant material used had much smaller leaves than sorghum, however the leaves grow directly from the branch and provide similar structure to sorghum plants. Testing consisted of securing the plant stalks between a wood vice and moving the vice under the corn head to simulate how the sorghum crops would move through the system in the field. The corn head was also lowered to the same height it would be operated in the field. Figure 3 shows the testing set up.

Figure 3. Testing set up using sorghum plants.

Testing with leaf material showed that the system properly engaged the plants and stripped the leaves from the stalks, however struggled to convey the stripped leaves into the harvester. The paddle chains worked as predicted and funneled the plant through the brushes. The first few plants fed through the system had the lower 2 ft of leaves removed, however the plants moved through the system too quickly and the upper portion of the plant was not in contact with the brushes long enough for the leaves to be stripped. The brushes were adjusted to allow for some interference between the back end of the brushes, which increased the contact between the brushes and the stalks and greatly improved the success of the system in stripping the leaves. Figure 4 shows the before and after photos of a sorghum stalk that had been tested. The brushes tear the leaves and damage the stalks when the plant moves through the system, however this is not a concern for RedLeaf. Additional testing is needed in the field to determine the ideal brush spacing, angle, and speed, as well as make any modifications necessary.

Figure 4. Before (left) and after (right) of a sorghum plant during testing.

The leaves stripped from five plants during testing were bagged and weighed; the leaves that remained on the stalk were also weighed and the difference in weights were used to determine the efficiency of the system. 338.7 g out of 623.8 g of leaves were stripped from the stalks, therefore the system is capable of harvesting 54.3% of the leaves on each plant. This is slightly under the goal of 70% leaves harvested per plant, however with modifications and additional testing the efficiency may increase. Only one small piece of stalk was harvested with the leaves, therefore the goal of no more than 40% stalk in the harvested material was met.

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