The Dynabee, also called a Powerball, Roller Ball or Dyna-Flex (not to be confused with the penile prosthetic), is a hand held gyroscopic device used medically for wrist and forearm therapy. It is also a toy, and when a speedometer was added to determine the rotor speed, competitions began to produce higher and higher speed values. The current record is over 16,000 rpm. A. L. Mishler developed the Dynabee and patented it in 1973 [1]. Since that time there have been a number references on the internet but, to our knowledge, only two refereed publications explain and rationalize quantitatively the strange behavior of this "gyroscopic device" [2,3]. The Mechanics 4423 attacked this problem with some success.

[1] A. L. Mishler, 1973, "Gyroscopic Device," U.S. Patent 3726146.

[2] D. W. Gulick and O. M. O'Reilly, "On the Dynamics of the Dynabee", ASME J.

of Appl. Mech. 67 321-325 (2000).

[3] P.G. Heyda, "Roller ball dynamics Revisited" Am. J. Phys. 70 1049-51 (2002); P.G. Heyda, "Roller ball dynamics," Math. Today 36 9 (2000).