Results
Summary:
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My device accepts and cuts up to a 1 ¾" limb.
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My device has a 55% cost savings from the original device.
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My device is 12.43% better in maximum force required.
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My device is 17.81% better in energy consumption to make the same cut.
Maximum overall force:
The following table and chart shows a true comparison between the Pellenc pruning head and the Wittig pruning head. Data includes the maximum force required to cut all the way through the same limb at the same diameter. At each subsequent larger diameter of branch, the heads were swapped to provide close comparison on the same test specimen.
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Three tests were performed at the same diameter for a more accurate average.
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The same limb was cut by both devices at the same date to compare averages directly. This allows the percent difference (% Diff) to be found.
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Average Percent difference (Ave. % Diff) to shows the maximum cutting force is 12.43% better than the benchmark.
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Implications of the chart.
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The Wittig green data looks typical for thicker branches requiring more force for a larger branch. However, the Pellenc appears to do better at the 1.25" diameter tests. This may be due to the increased contact area of the cutting edge on the Wittig blade. This would only matter as the comparative blades are at the highest force. The profile of the Wittig blade is shown below right, at the top edge of the von-Mises stress map.
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Beyond 1.25" diameter, the Pellenc head could not accept a limb to cut. Therefore, at the 1.75" test, the pellenc lacks data.
Green branches 5/8 to1.75 (in.)
Blade contact length inside the cut.
The chart clearly shows the difference between the cutting heads. Even with the anomaly of the Pellenc data at 1.25", the trends are obvious.
Dry branches only from 5/8 to 1.75 (in.)
Work / Energy Comparison:
The force data at any one point can be multiplied by the partitioned change in distance to give the work done at any single time. The distance is calculated using the rate of travel chosen prior to the test. The time accrued can be gained by subtracting the time of the final data used, less the time value at the first data used. The work performed in these times are then summed to give the overall work done in the significant cutting function. These produce a pound-inch unit and can be converted into Watts. As seen in the example calculation, the lb-in value is 268.043 (lb-in.)
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The graph of the data in excel produces a trend line that can be used to validate the calculation. The area below this line represents the work done by the cutter over the entire cutting function. The integral of this function provides a means to double-check the validity of the calculated lb-in value. As seen in the chart below, the 257.569 (lb-in is only 3.9% different than the value given by the summation.
Example Raw Data Calculation
The summation of the right column represents the total work done throughout the cut.
Example Poly Trend-line with Equation
Example Calculation
This calculation offers validation of the value between the data sum and the integral of the trend line during the substantive data.
There is only a 3.9% deviation.
This data is accurate and is reproduced for each test sample. The following table was built using those numbers. The comparison begins with an average value gained from each device. Then the percent change for the better is calculated. 17.81% is a significant energy savings.​
This means that you could use a 17.81% smaller battery. Or run the cutter for 17.81% longer in the field with the same battery.
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