The scratch tester is designed to be a cheap, accurate, and consistent device to test coefficient of friction. To design the best scratch tester possible certain features should be emphasized such as: cost, the dimension of the machine, and the hazards that could come with operating the device. The machine should be able to apply a weight in a range from 5-50 N. The plate should move from approximately from 0-5 m/s. Lastly, to record the data a load cell with a range of around 5-100 N would be optimal.
Proof of Concept
For the proof of concept, the team will construct a model to test for a certain value of interest. To do this they will build the model shown in figure 1 by using wood, aluminum rails, nuts, bolts, bearings and a weight. Once the construction is complete, the team will apply the weight to the wooden plate and pull the plate with a spring scale. The team will record the force from the spring scale right as the plate starts to move. This test will answer the question of how much force will be needed to move the plate which will in turn give the necessary torque that a motor will need to provide in order to move the plate with the applied load. The testing of the proof of concept will be done on 12/17/16 and the results will then be analyzed, giving the team the necessary knowledge of what motor to use for the scratch tester project.
The Couginator is a project to develop an affordable and accurate scratch tester. A scratch tester is a device that can determine the coefficient of friction between two surfaces. Team 26’s scratch tester, The Couginator, would look like a common microscope to the untrained eye due to its size and shape. It has overall dimensions of 30cmX22cmX15cm and has the notable features of a cantilevered arm, base, and movable specimen plate. This cantilevered arm is weighted and applies a force through a scratching pin to a specimen on the movable plate. This plate is then moved along the tracks to a distance of up to 10 cm and the reaction forces of this interaction is recorded. These reaction forces are recorded on a computer program and used to give vital information about the material contact, like the coefficient of friction. The overall goal of this project is to get the product accurate to the 0.1% of the actual value and still be cheaper than $750.
The Couginator project will be useful for the consumer by not breaking the bank. The scratch tester that is used on the University of Nevada, Reno’s campus costs over $200,000 and is over 7 feet tall. Having a convenient and affordable scratch tester will greatly benefit the consumer.
The Cougniator Scratch Tester was fabricated at the University of Nevada, Reno’s machine shop. The project can be split into five main subassemblies: moving plate, specimen plate, the scratching arm, machine base, and the pin holder.
The pin holder was a bundle purchase that was designed to hold a pin. The gearing system for the moving plate was 3-D printed in the machine shop. The moving plate is 3-D printed at the Delamare Library. Three other necessary subassemblies are manufactured in the machine shop. The machine base was cut using a Bridgeport Mill to shape and drill assembly bolts. The arm subassembly has be shaped with the Bridgeport Mill Machine. The specimen plate is securely mounted with screws on an L bracket. Another set of screws will be placed on the outside of the bracket to screw down allowing for the specimen to be clamped in place.
Testing and Results
First, we downloaded the Phidget Drivers and opened the Phidget Control Panel. Then, we plugged in the USB attached to the Load Cell. We calibrated the Load Cell by using no weights and then adding weights. This should give you a formula to calibrate your Load Cell. Then, download the Flowbotics app. Turn on the data logging located on the right while moving the specimen plate with the scratch tester. This should allow you to record the horizontal force on the specimen. Afterwards, open the log file with excel. Use the correct formula and plug in the formula for calibration to obtain the coefficient of friction. You can compare the measured and actual values afterwards. Take a look at the screenshot below.
The team tested the product on two materials: wood and plastic. In the screenshot above, the measured coefficient of friction was 0.1926 and the actual value coefficient was 0.2. The team’s value was extremely close to the actual value. After multiple tests, it did not fail at all. The values were consistently close to each other. The Team’s Scratch Tester can be used to determine the coefficient of friction of any item. A real world application is this can be used to determine the stopping force of Brake Pads.
Meet the Team
Arlis Meyer is Mechanical Engineering student from Cool, California. In his schooling career, he has accomplished all core classes and prerequisite courses up to this point. He plans on graduating in the Spring of 2017. After Graduation, Arlis plans to get a job in the engineering field and pursue a career as a mechanical engineer.
Benjamin Lillig is a senior at the University of Nevada, Reno perusing his bachelors of science degree in Mechanical Engineering. Before moving to Reno for school in 2013, Ben resided in San Ramon, California. After graduating in the spring of 2017 he plans on beginning his career as an engineer.
Hello all, my name is Mitchell Schildge from Truckee, CA. Mitchell is a super senior majoring in Mechanical Engineering at the University of Nevada, Reno. In addition to this major he will also graduate with a Renewable Energy minor. When not working on a human power vehicle or school work he is backpacking, rock climbing, and skiing. After graduation he will begin the Pacific Crest Trail, then seek a renewable energy job or internship.
Jeff Liang is a senior mechanical engineering student who will be graduating Spring of 2017. Classes he has taken that will be relevant towards engineering jobs is: computer data acquisition, instrumentation, and mechanical design. These classes have made him proficient in Excel, SolidWorks, and Matlab. He is originally from Las Vegas and decided to pursue a degree in Reno. After graduation, his goal is to be proficient in mechanical design and pursue a job in it.
Riley Roberts is a mechanical engineering student in his senior year. He is pursuing a bachelor’s degree. Riley is homegrown from the state of Nevada, here in Reno. After graduating he plans on finding a job in Reno or on the west coast related to engineering and the outdoors.
Development Technician – Tony Berendsen
Arpith Siddaiah – Ph. D student at field of Tribology