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Pure Motion


By Bethany Halford

When Francis C. Moon came to Cornell University in 1975 as a professor of engineering mechanics, he had no idea that priceless treasures lay half forgotten in the school’s closets. Over time, Moon learned that a historic collection of 230 mechanical models—the largest surviving collection of Reuleaux models—were hidden away in neglected storage areas, dusty cabinets, and even a boathouse.

The Reuleaux models were the brainchild of the 19th-century German engineering professor, Franz Reuleaux (1829-1905), who was known for his theories on kinematics—the science of pure motion. As part of a systematic study of basic mechanical building blocks, Reuleaux designed and built more than 800 different models, each embodying a basic machine element. He used the models for research and as a teaching tool, and in the 1870s he authorized the German manufacturer Gustav Voigt, Mechanische Werkstatt, to reproduce 350 of them so that they could be used to teach engineering students throughout Germany and around the world.

“When I first came to Cornell, I didn’t know about this collection,” Moon recalls. “But then I got a letter from somebody in Berlin looking to buy the collection, so I knew I was on to something.”

With a little detective work, Moon learned that in 1882, Cornell’s president, Andrew Dickson White, used an $8,000 donation to procure more than 250 of the models. Within 75 years, the investment would prove to be priceless. The majority of the models made from Reuleaux’s design stayed in Berlin, where they were destroyed during World War II. Collections in St. Petersburg, Russia, and at Montreal’s McGill University have also been lost, making Cornell’s the largest known collection of kinematic models designed by the founder of modern kinematics.

As a land grant university, Cornell needed a curriculum in the “mechanical arts,” and the Reuleaux collection was meant to equip the mechanical engineering department with teaching tools that combined mathematical fundamentals and practical, hands-on learning. Reuleaux himself supervised the models’ shipment to Ithaca.

Although they had once been the prized possession of the department, the Reuleaux models eventually fell out of favor. Students came to the university with more than enough hands-on mechanical engineering experience, having tinkered with farming equipment, automobiles, and other machines as youngsters. Kinematics fell out of fashion as an independent engineering course by the 1960s. Engineers still learned kinematics as part of coursework in dynamics, and more often than not, the subject was taught using mathematics rather than models. As is inevitably the case with most wonders of a bygone era, the Reuleaux collection was packed away in old wooden cabinets in Cornell’s computer science department, largely forgotten by the school’s mechanical engineers.

When Moon found out about the Reuleaux collection, he says that “most of the models were in a state of benign neglect. They hadn’t been used, but they hadn’t really deteriorated either.” Even after 120 years, all but one of the brass and cast iron models show no rust and all but six are still in good working order. This remarkable resilience, Moon says, can be credited to Reuleaux. He understood that working with the models would be a tactile experience for students; they would want to handle them and make them move. So he created the models’ cast iron with an alloy that would be rust resistant.

Along with the Reuleaux models, Moon unearthed a number of fascinating other mechanisms. One of the first motorized calculating machines, known as “The Millionaire,” was found in a janitor’s closet at Cornell.

Perhaps no one has benefited from the rediscovered kinematic models more than Cornell’s engineering students. Moon and several other faculty members at Cornell routinely use the devices as teaching tools. In the electronic age, youngsters just don’t tinker with machines the way that they once did, Moon says, and using the machines helps them gain a sense of three-dimensionality: “As soon as you see the models doing something you want to know why.”

Moon, along with his colleague Hod Lipson, designed a lesson he calls “Leonardo in your toothbrush” as part of a sophomore design synthesis course. Students get an inexpensive electric toothbrush to take apart and analyze in terms of the models in the Reuleaux collection. One of the models they use is the Slider-Crank model—a mechanism that converts rotary motion into alternating linear motion. The slider-crank is one of the most ubiquitous mechanisms in the world today. Its design can be traced back to the drawings of Leonardo da Vinci. So the students have an opportunity to draw links between the history of engineering and modern engineering design. “When you look at these machines, each model embodies a different track of history,” Moon says.

Cornell’s engineering students can’t seem to learn enough about the Reuleaux collection. “One of our problems is that now students are banging on the door trying to get to use the models,” Moon jokes. Because of their immense popularity, he has set aside one week during the year for students to tinker with the devices.

And the models haven’t been of interest just to engineers. Cornell’s mathematics and architecture faculty find them fascinating. The chair of the sculpture department at the Rhode Island School of Design sees them as works of art and thinks they would be useful for teaching kinetic sculpture. And Moon says that “local high school teachers love these models.”

Naturally, the popularity of the priceless collection poses a problem for Cornell. How can students and educators make the most use of the models without running the risk of damaging them? John M. Saylor, director of Cornell’s engineering and computer science library, had an idea.

Working with Moon, several members of Cornell’s mechanical engineering and mathematics faculty, and a handful of dedicated staff and students, Saylor is spearheading an effort to create a digital library of kinematic models that will be available on the Internet as part of the National Science Digital Library. The group won a $725,088 grant from the National Science Foundation for the project.

Known as the Kinematic Models for Design Digital Library, or K-MODDL, the digital library will feature the Reuleaux collection along with Cornell’s other kinematic models. Free via the Web, Saylor says K-MODDL should be up and running by the end of June at http://kmoddl.library. Until then, eager visitors can visit the Web site for a taste of the projects, and Saylor will present a talk about K-MODDL at ASEE’s 2004 annual conference in Salt Lake City.

K-MODDL will feature photographs of each mechanism accompanied by a description of how the model works, the theory and history behind its design, and, in most cases, an example of a machine that incorporated the mechanism. The library will also include resources such as historic engineering texts, literature on kinematics and Reuleaux, and teaching modules that demonstrate how the models might be used in the classroom at the undergraduate, high school, and middle school level.

Saylor says that because “the models are really meant for moving and for people to handle them,” it was important to give K-MODDL’s visitors more than just a still-life catalog of kinematic devices. So, each model will also be captured in a movie that users can control with a computer mouse. Move the mouse from left to right and the model operates in one direction; move it from right to left and the model operates in the opposite direction. The speed with which it moves depends upon how quickly the user moves the mouse.

But the K-MODDL team also wanted to give people an even deeper understanding of how the models work. “We were really looking to find an edge over conventional libraries that just offer pictures, movies, and text,” says Hod Lipson, a professor of mechanical engineering and computer and information scientist who is one of the project’s collaborators. Reuleaux designed many of his mechanisms so that they could be taken apart and put back together in different ways to see how their changes affected the mechanism. By adding moveable virtual models to the library, K-MODDL’s developers hope to offer a similar experience.

“You can take the machines apart or modify them,” Lipson says of the virtual models. “Doing so really allows you to play with it and explore a lot more of the design space. The interaction lets you ask ‘What if?’ questions. For students, the ability to experiment with machines and get immediate feedback is very important. When I studied kinematics it was through equations, and you had to visualize the motions through equations. Sometimes we saw simulations, but they weren’t interactive. What we have now allows you to do this in real time.”

Even with all that can be learned from the movies and interactive virtual models, the K-MODDL team recognizes that experiencing the Reuleaux collection in two dimensions has its limitations. So they created a feature that will let visitors to the site make their own Reuleaux collection using 3-D printing files.

Three-dimensional printing is often used to make plastic prototypes in order to get an idea of what a product will feel like. “We thought that we could harness this type of technology to bridge a gap between the digital Web abstraction and the material world,” Lipson says.

Although the printers cost as much as $100,000, the prices have been decreasing and the printers are becoming more commonplace at universities. Individual printouts can be purchased from a printing service. Lipson says the printed plastic Reuleaux models look and function in the same way as the originals, they’re just made of different material. “We can recreate the lost models; we can duplicate existing models. We can duplicate models from around the world to complete a single collection,” he says. “This really opens up the possibility for … more access to the collection than would have been available before.”

Ultimately, the group hopes K-MODDL will spark an interest in the workings and history of kinematics and engineering among engineers and students as well as the public at large. “Having it on the Web really allows people to simply see the machine, grab it, push and pull it, and see the experiment. Anyone can use it without any prior knowledge,” Lipson says.

“Most people could benefit from using models of any kind. I think it helps your abstract thinking even if you’re not going to be an experimentalist or an engineer,” Moon adds. “Our goal is to present this collection to the entire world.”


Bethany Halford is a freelance writer based in Baltimore



Man Behind the Models

Franz Reuleaux was neither an inventor nor a pure scientist. Rather, “he personified a new figure in the industrial age, the engineer-scientist,” writes Cornell mechanical engineering professor Francis C. Moon in Applied Mechanics Reviews. “Unlike the craftsman-engineer who believed in trial and error, hands-on education, the engineer-scientist believed that machines could be created and designed using scientific principles guided by rigorous mathematics.”

Machines were in Reuleaux’s blood, so to speak; both his father and grandfather were machine builders. Reuleaux’s study of the scientific principles that underlie machines earned him an international reputation and the moniker “the father of modern kinematics.” Reuleaux was born in 1829, a time when most people regarded machines with awe. “He who best understands the machine, who is best acquainted with its essential nature, will be able to accomplish the most by its means,” he wrote.

But to describe Reuleaux as a professor and kinematic theorist alone gives an incomplete picture of the man. His extensive writings include the engineering books The Kinematics of Machines and The Constructor as well as a German translation of Longfellow’s Hiawatha. —B.H.



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