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By Design News Staff -- Design News, April 8, 2002
Future engineers
Following up on your article about Robolab (DN 02.18.02), there is a K-12 initiative in Rochester, NY which has been using Lego hardware for 10 years; with great success. Check it out at http://www.e3fair.org/. Initially, we had annual competitions where students built a race car, a tractor, or a crane. Over the last two years we have added the PLC noted in your article, and have Middle School, student-built robots moving pop cans or playing hockey. If nothing else, I am hoping to add our experiences to your repertoire of success stories!
Thanks for the article.
Jon Kriegel, Mechanical Engineer, Eastman Kodak Company, Past Chair, E3 Fair
Patent office doing its job?
In your recent editorial (Sleepless in your SUV, 02.18.02) you stated that IBM was awarded a record 3,411 patents last year. While IBM may be a true innovator, this might also reflect that the patent office is simply not doing its job.
They'll issue a patent for anything and let the courts handle disputes. Thus the validity of a patent is determined by the one with the most money for lawyers.
Scott Lynch, Half Moon Bay, CA
Mismatched tires, revisited
Regarding your article on mismatched tires (DN 01.21.02), I question the conclusion drawn in this case. I was thinking that the difference in braking torque of the smaller radius tires would be offset by their higher rotational speed relative to the front. Also, that lower profile tire may have more contact area than the OEM tire, and thus more resistance to lockup. A more likely explanation is the typical unloading of the rear tires of any vehicle in a panic stop, approaching lock-up, magnified by the poor weight distribution of the unloaded pick-up truck.
A more serious problem in this case, although probably unrelated to this accident, is the use of a tire with a lower load rating than the OEM tire. By my estimation, the equivalent load tire for a 215/75 would be a 235/65 in that profile. Thus, the Avalon 205/65 tire was 3 steps below in the sizing system for load rating. This, I am sure, would present a greater issue in the long run with heavier loads.
Thanks for some interesting and thought provoking articles!
Rogert Schwartz, Design News reader
Terrible tire tale
I have a similar tire story to the one told in Design News about the mismatched tires. In 1973 I purchased a used Triumph Spitfire. The first day I drove it to work, while making a left turn across a divided highway, I spun out, at least 180 degrees. Fortunately I did not hit anything. After gathering my wits, I drove slowly to work and then examined the situation.
1. Tire pressure was low.
2. Two tires were one size larger than correct.
3. The other two tires were two sizes larger.
4. Each size was mounted crossed, i.e., different sizes on each axle, and different sides of the car.
5. This car had swing axle rear suspension.
I immediately put the larger tires on the rear axle and corrected the tire pressure, making the car considerably safer.
Thanks for the story about the risks with incorrect tire sizes.
Dan Nibbelink, Colorado WaterJet Company
Fender bender question
I am a new reader of the magazine, and I enjoy reading the "Z Files" on your back page. I would like to ask the column's author a question: If a car has a constant speed (acceleration = 0) and hits another car, how can I calculate the force and stress?
Sinsa Sehovac, Kitchener, Ontario
Zirkle's response: The force is not easily calculated. From dynamics, we know that the change in momentum (mass x velocity) is equal to the impulse (area under the force vs time curve during impact). If you assume the force is constant (which it never is), the impulse is equal to the force x time. (If you know the time over which the impact happened.) Usually, we have to know the crush characteristics of the specific vehicle. If you know the amount of crush, you can relate this to the peak force during impact. One reference on this procedure is "Forensic Engineering Investigation," by Randall K. Noon, CRC Press, ISBN # 0-8493-0911-5. And keep on reading Design News—I am dealing with this issue in an upcoming article.
Engaging engineers
The article "Engineers Making A Difference" (DN 12.17.01) was excellent. A program mentioned in the article, Project Lead The Way, engages engineers nationwide as mentors, advisors, and consultants.
The altruistic and patriotic mission of this not-for-profit organization is to solve the shortage of engineers and engineering technologists in our nation, a topic of interest we mutually share. I invite your readers to visit our website, www.pltw.org, for additional information.
I enjoy Design News a great deal. Thanks!
Niel Tebbano, Director of Operations, Project Lead The Way
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