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Son of Toby

Robotic Arm Project

A student research project supported by the Drury University Physics Department , in conjunction with the NASA Reduced Gravity Student Flight Opportunities Program.


Older version of the Son Of Toby robotic arm shown here at Ellington Air Force base before the 2007 flight.

Some of the theory behind the project. A regular class period in progress....

In order to improve our understanding of how the brain controls the human arm both in the presence and absence of gravity, we have developed a two-degree-of-freedom robotic arm which is driven by six servo-actuated viscoelastic muscles. These muscles represent abductor-adductor muscle pairs similar to the many such pairs that drive the human arm. Our robotic arm exhibits planar motion with two degrees of freedom about two joints. The computer-controlled servos mimic the contractive action of the sarcomeres in actual muscles, while sections of elastic tubing represent the elastic behavior of actual muscles. Motion is recorded with optical encoders built into each joint axis. Our prepared experiment is a purely feed-forward system, and our goal is to determine whether our equations of motion, when numerically integrated, will predict the observed motion of the arm within experimental uncertainties. During the 2009-10 academic year, we developed a one-degree-of-freedom arm that also used servo-actuated viscoelastic muscles. In years past other students have done research on both one and two degree of freedom arms. In 2006 a group of students participated in the NASA Reduced Gravity Student Flight Opportunities Program, using a two-degree-of-freedom arm. However the arm was roughly machined and was only able to execute planned motions very crudely. Since then more arms have been built and experiments done at our university. More sophisticated equipment has been incorporated, and the design of these arms has improved. Our research builds on that done by those before us, but we intend to expand and refine the experiments done in past. In particular, we plan to include accelerometers in our experiment that will measure the two components of the effective gravitational acceleration in the plane of the motion, thus allowing us to better explain the observed trajectories after the data are gathered.