Here is the abstract of the science fair project that I conducted this year.
This experiment is to determine if interlocking surfaces, specifically carpet and tank tread, follow the same rules of friction as regular, smooth surfaces, including that friction is not a function of area. The variables of weight and area were independent, and the friction force was the dependent variable. It was hypothesized that the friction would be a function of and vary directly with area. It was concluded that although the experimental design did not allow for completely accurate data, a trend in the results still showed that friction is an inverse function of area. When the surface area went down the friction increased, which could be caused by increased pressure. The pressure could have had more of an effect on friction force than the number of interlocking pieces in the tread.
Discussion of the experiment is included in the attached Word document and the data and results are included in the attached Excel spreadsheet in the next post.
Results & Discussion can be found in the white papers:
IBApril180, I found this paper to be quite interesting. It’s good to see some empirical data to help us deal with the old arguments about surface area and traction. Do you have plans to perform more experiments?
I think it would be very helpful if someone were to test tractive materials commonly used on FIRST robots, with a normal force around competition weight. It would be very, very, useful in selecting the proper tread for the amount of torque one’s drive train can safely provide. Research into why some materials are “stickier” than others would be great, too.
This looks like a cool science fair project! I hope you have plans to continue working on this! You could make a very valuable database out of it. Thanks for posting it!
The most interesting thing I saw was that increasing the contact area at high normal forces degraded the performance faster than increasing the contact area at smaller normal forces. That’s just the opposite of what I expected. It didn’t surprise me that the loads went down with increased surface area, I just thought that your force vs. pressure curve would be more linear.
Very interesting, maybe the carpet interacting with the edge of the material is a significant factor?
I do hope to conduct more experiments in the future. Maybe I can set up a more efficient way to measure the friction or make it more specific to the machines that we are using in competition. Let me know if you come up with any ideas.