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. Building One-of-a-Kind Robot to Test in Zero-Gravity

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by Stacy Shoemake
Springfield MO (SPX) Jul 8, 2004
Will a cat still land on its feet in zero gravity? That's the question four Drury students are attempting to answer when they travel to the Johnson Space Center as part of NASA's Reduced Gravity Student Flight Opportunity Program this July. The idea began as a class project in Dr. Greg Ojakangas' Mechanics II course in the fall of 2003, but student interest in angular momentum in microgravity helped morph the idea into a fully realized experiment. Their goal is "to test the feasibility of a device that allows for rotation of objects in zero gravity, while maintaining a net angular momentum of zero."

Angular momentum is the basic idea that a spinning object posesses a momentum of spin, or angular momentum, which can be thought of as a tendency for spinning objects to continue to spin. The robot is designed to execute a net rotation while maintaining a net angular momentum of zero.

Their robot presents an alternative to the reaction wheel -a device which is commonly used to rotate satellites in outer space. Because its motion superficially resembles that of a ratchet wrench, they're calling the experiment "The Orientation Ratchet: A Novel Concept for Producing Net Rotations in Zero Gravity."

The proposal submitted to NASA for program consideration describes their research by saying: "At the beginning of its motion, the mechanism containing the extendable masses will be closed, with the masses close to the central axis of the robot. "It will then extend in a manner similar to the opening of an umbrella, increasing the rotational inertia of the upper section, which will then rotate relative to the lower section by a specified angle. "The upper section will then contract, and the relative motion will be reversed, returning the robot to its initial configuration. This series of actions leads to a net rotation of the robot, while its net angular momentum remains zero."

The first part of the project involved nearly five months of mathematical experimentation. When the team felt confident that they were working with the right equations, they set out on the challenge of creating a robot from scratch. Daniel Ratchford, Jeremy Woolery, James Stockton and Alison Harris have spent the past four months creating a device to test their theory.

The robot is a rather simple device, consisting of a programmable central processing unit called a "brainstem" (marketed by Acroname Corporation), three servos and a port giving the team instant access to the brainstem. Daniel Ratchford, the only member of the team in a computer class this semester, designed the program used in their experiment.

"The brain stem hooks up to the servo, and with my program, I can tell the brain stem to tell the servos to rotate to certain positions, then tell the servos when they need to rotate, at what time, and how far to rotate," said Ratchford.

The team has met frustrations along the way, but have relished the process of experimentation in the laboratory. Their concept has never been attempted before, so the team must create the map that would guide future research of this nature.

"The most frustrating part of the experiment has been the actual fabrication of the robot. It's a relatively simple matter to show that it should work, but an amazingly difficult exercise in precision to actually get it to do what we want," said James Stockton.

Stockton is a senior majoring in physics and mathematics. The project has given him a great sense of accomplishment because it's something that's never been done before. It's also greatened his level of confidence because Ojakangas has given the students freedom to develop, design and implement the experiment without much interference, even on tasks he assumed would require close interaction.

"There were many challenges in designing the robot. It was something that had never been done before. Taking the concept and putting it into a mechanical structure was a brand new thing and they did a great job. Then they had to program it, and that was a potential subject of tension - so I promised them once we got to that point, I would help them. But I came in one day, and it was finished. That was really a challenge, and they lived up to it," said Ojakangas.

While Ojakangas is continually impressed with the level of independent work the students are producing, his students feel thankful for the freedom he gives them with the research.

"Dr. Ojakangas is really great to work with. He keeps us aware of the many varied things we need to accomplish, but also allows a lot of freedom in getting them done. He doesn't micro-manage it (the experiment), which both frees us to get things done in the order that seems best and gives us a confidence boost because we understand that he knows we can get things done on schedule," said Stockton.

Alison Harris, a senior majoring in physics, agrees that the actual fabrication of the robot has given them the most trouble, but she feels the extra challenge has provided her with a truly rewarding experience.

"Trying to find the parts and pieces and getting the robot to function the way we want it to has been very challenging…But seeing it go from an idea to actually functioning has been very rewarding. When I think about everything we've done so far, it's amazing to see how much progress we've made and how all our thoughts and ideas have come together," said Harris.

To understand the concepts necessary for their experiment to be successful, the group used Newton's laws of rotational motion. After they understood how the different parts of the robot would react, it was a matter of adding mathematic equations to find angular velocity, angular momentum and rotational inertia.

Once the robot reaches the final phase of construction and all problems have been resolved, the Drury researchers will be ready for their trip to NASA to test their robot in the environment it was designed for: zero gravity.

"As interesting as the project's concept is, I must admit I'm most excited about personally experiencing microgravity," said Stockton. "The idea of experiencing the same sensations as an astronaut, even though I'll never be leaving the confines of earth's atmosphere, is incredibly appealing."

Stockton graduates in May, but has plans that will keep him looking to the sky. He'll be heading to New Mexico State University to pursue a doctorate in astronomy and astrophysics.

Related Links
Reduced Gravity Student Flight Opportunity Program
The Orientation Ratchet
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