Element I: Testing, Data Collection, and Analysis

Introduction

In the design process once a prototype is made, it's important to thoroughly test the prototype to assess the strengths and weaknesses of the design. To test our lunar shoe we made a multitude of tests which we used our prototype to collect data on our design. We will be testing for the coefficient of friction in multiple tests, static charge, durability, functionality, sizing, and more.

Test Results

5.5" x 6" sheet friction test three COF #2 test

The Tan(90)=undef or the lim as theta goes to 90 of tan(theta) = infinity. There can be an infinite coefficient of friction which means that there is some other force between the rubber sheet that helps the rubber stay together. Further testing is required to see if this force is strong enough to prevent slippage, and will be long lasting when worn to be effective enough.

Shoe friction test three COF #2 test (angle test)

Tan(80)=5.671. Unlike with the original test the shoe slipped before 90 degrees which means the unknown force in this setup is not present or not existent. This shoe has gone through previous testing which wore it down which could have decreased the adhesive force on the shoe. Another possible reason is the greater weight on the shoe with the shoe part applied more force which overcame the adhesive force. Regardless of this force being present or not, the COF of 5.671 exceeded the requirement of a COF of 3 for an equivalent frictional force in 1/6th gravity as on Earth.

Pulley test

700/215 = 3.256. This test indicates that COF on the shoe is at least 3.256. During this test we encountered problems with getting the string to mount to the shoe so in the orientation we had the string the string kept on peeling the shoe off which weakened the shoe ability to stay. Future tests involving pulling on the shoe with a string would need to find a better place and method to mount the string.

Harness test

For the harness test we used a pulley that had a mechanical advantage of 7:1. Andrew Schaefer weights 162lbs since the harness had to to hold 5/6th of Andrew's weight so that in combination with the mechanical advantage means there needed to be around 20lbs on the input rope. While strapped up in the harness Andrew was able to swing by pushing onto the silicone floor with the shoe. However, Andrew was still able to push off the tile floor with the sock, however, when he did, he had to push hard onto the floor to prevent slipping. Also, every time Andrew pushed onto the ground less of Andrew's weight was supported by the harness. One improvement would be to put the pulley on a rail system which would allow the subject to walk with the harness.

Varied Weight Test

In the varied weight test we added weight to the top of the shoe and then pulled the shoe until it slipped, we then graphed the maximum force until the shoe slipped. We then graphed the relation between the slippage force and normal force. The relation followed a linear relationship which relates to the equation Frictional force = Coefficient of friction * Normal Force. Based on this test we measured a coefficient of friction of 2.08. This is less than CoF needed of 3, and below the angle test which we got a CoF of 5.671 and the pullet test which got a CoF test of at least 3.256. Even with this lower number our harness test did show that we were able to walk with 1/6th gravity.

Static test

For the static test we began by rubbing the shoe against the silicone floor material and tested the amount of static electricity generated on an electroscope (Figure 1). While doing so we also took humidity measurements using our Sling Psychrometer (Figure 2) to allow us to compare humidity during our tests to the humidity on a possible lunar habitat. Our test found that the average angle of deflection by the electroscope was 4.857 degrees. We did receive a single data point that we felt was an outlier since the angle of deflection was 60 degrees. We believe this data point and some of the other larger data points were due to the silicone floor silicone rubbing against the table, which charged the floor silicone, which then passed on some of it's charge to the shoe. After doing a test on where we rubbed the floor sheet on the table, we measured an angle of deflection of 90 degrees, which supports our theory. This problem would be mitigated in the final lunar habitat where the silicone floor would be firmly be secured to the other layers of floor, preventing the silicone floor to rub. During the test we also observed no visual arcs, meaning that there is a low likely hood of it starting fires, and that any charged built up on the electroscope quickly dispersed.

Multi size test

This shoe fits on people with a shoe size of 12 to 7. This demonstrates that a single shoe size can fit multiple different people. This shows that we can create generalized sizes for each range of values, sticking with a small, medium and large. The also allows the manufacturing cost to be cheaper and in a commercial setting would allow less machining complexity.

Wear Test

After prolonged testing on our original prototype floor experienced some wear and tear. We theorized that this was do to the quality of the original floor during the setting process since there was a spot that didn't fully solidify after the rest of the floor did. This is backed by the fact that the sole which did not have difficulty during molding. I then remolded a new floor sheet and did a test were we rubbed the shoe on the floor 300 time since that is how most of the damage occurred during the static test were we rubbed the shoe 300 times. After the initial 300 we rubbed the shoe another 700 times, and after all these tests, there was no visible damage.

Conclusion

From our testing we found that our design and materials were mostly ideal for the shoes we were trying to design. The static electricity tests and all tests that tested friction gave us promising data that our materials and design were good for the shoe. The qualitative tests showed that the material we are using could have a higher durometer as we are using a durometer around 30A (around the toughness of a pencil eraser).