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Requirements:

 

Design Requirements (Entire Pruner):

  • Capable of cutting 1.75" diameter branch-------------------------------------------Not Tested

  • Cutting blade must be at least 30” away from trigger -----------------------------Passed

  • Must weigh less than 3lbs -----------------------------------------------------------Passed

  • All components must cost less $500------------------------------------------------Passed

 

Design Requirements (Cutting Blades):

  • Open at least 1.75” in middle of blades----------------------------------------------Passed

  • Weigh less than 1lb-------------------------------------------------------------------Passed

  • Each blade must be less than ¼” thick----------------------------------------------Passed

  • Capable of cutting 1,000 branches without need for maintenance/sharpening--Failed

Test 2: Time to complete cutting motion

Introduction: The time to complete the cutting motion is an integral aspect of this project. If the pruner took an absurd amount of time to complete a cut, it would be nearly useless. As discussed in the initial design of the project, the pruner should only take a few seconds to complete an entire cutting cycle. The complete cutting cycle includes closing the blade until the cut is complete, and re-opening it to the “fully open” position where a new branch can be positioned inside the cutting mouth. It was calculated that a full cutting motion with no resistance would take 3.50 seconds to complete. The calculated time for the full cutting motion with the resistance of a branch was 5.00 seconds. The process for this test includes steps 10a-10g on the Gantt chart.

 

Method/Approach: This test will be scored by the pruners ability to complete a full cutting motion as quickly and efficiently as possible. The resources required to complete this test are two test personnel, the pruner, 1.0” diameter branches, and a stopwatch. Data will be captured by using a stopwatch to time the cutting cycle. This test should be performed with a fully charged battery in the impact drill. The precision and accuracy of this test is determined by the instruments used to collect data. For example, the calipers have a tolerance of ± 0.001”, and the stopwatch is only going to be as accurate as the user, so I would say it has an accuracy of ± 0.25 seconds. The data for this test will be compiled into a table and then converted into a graph to show the results more visually. This test will be completed 4 times, each with 20 trials. The first of the four trials will be with a soft trigger pull on the impact drill and no resistance to the blades. The second will be with a hard trigger pull on the impact drill and no resistance to the blades. The last two will be the same as the first two, but with a 1.0” diameter branch to represent a real-life use situation.

 

Test Procedure: The test procedure includes the following:

  1. For the first round of tests (soft pull, no resistance):

    1. Gather apple tree branches, pruner and a stopwatch.

    2. Begin with cutting blades in open position.

    3. With a soft pull on the impact drill trigger, complete a full cutting motion. The second tester will time the cycle by starting the timer when the blade begins to move, and stop the timer once it reaches the fully-open position.

    4. Record time for cutting cycle and repeat 19 more times.

  2. For the second round of tests (hard pull, no resistance):

    1. Gather apple tree branches, pruner and a stopwatch.

    2. Begin with cutting blades in open position.

    3. With a harder pull on the impact drill trigger, complete a full cutting motion. The second tester will time the cycle by starting the timer when the blade begins to move, and stop the timer once it reaches the fully-open position.

    4. Record time for cutting cycle and repeat 19 more times.

  3. For the third round of tests (soft pull, branch resistance):

    1. Gather apple tree branches, pruner and a stopwatch.

    2. Begin with cutting blades in open position.

    3. Place 1.0” diameter branch into the cutting mouth.

    4. With a soft pull on the impact drill trigger, complete a full cutting motion. The second tester will time the cycle by starting the timer when the blade begins to move, and stop the timer once it reaches the fully-open position.

    5. Record time for cutting cycle and repeat 19 more times.

  4. For the fourth round of tests (hard pull, branch resistance):

    1. Gather apple tree branches, pruner and a stopwatch.

    2. Begin with cutting blades in open position.

    3. Place 1.0” diameter branch into the cutting mouth.

    4. With a harder pull on the impact drill trigger, complete a full cutting motion. The second tester will time the cycle by starting the timer when the blade begins to move, and stop the timer once it reaches the fully-open position.

    5. Record time for cutting cycle and repeat 19 more times.

 

The entire test procedure should take approximately two hours and can be completed at CWU. The only safety precaution to be aware of is the dangerousness of the cutting mouth. Do not put fingers or anything other than a tree branch inside the cutting mouth.

 

Deliverables: The deliverables for this test will include a table with the results for each trial, as well as graphs of the times in order to better compare the efficiency of the cutting cycle. The test will be a success if the pruner completes the entire cutting cycle in less than 3.50 seconds without resistance and 5.0 seconds with the resistance of a 1.0” branch.

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RESULTS

In conclusion, this test was very successful with no resistance. However, when the portion of the test where the pruner needed to cut through branches, the housing pieces of the pruner failed, leaving that part of the test as a failure. As seen below in figure 3 and figure 4, the test was unable to continue due to the failed parts of the pruner. Without resistance, the pruner performed very well. With a soft trigger pull the pruner was much more consistent for each time to complete the cycle, whereas with a hard trigger pull the pruner was very inconsistent. With the hard trigger pull it would either complete the cycle very quickly (as low as 2.0 seconds), or very slowly (as high as 6.5 seconds). This inconsistency was due to the drive components not being perfectly concentric, causing hang-ups in the linear actuation of the drive shaft. However, when the trigger on the impact drill was pulled softly, resulting in a slower rotation of the lead screw, the cutting motion was much more consistent and still achieved a lower than calculated time of 3.0 seconds (average).

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