Orbit Machines:  Evolution
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Orbit 1, 2006, 2 stainless steel tube spokes, 24" swept diameter
Orbit 2, 2006, 6 stainless steel tube spokes w/ different color LEDs, dynamic balancing via on-spoke weights, 25" swept diameter
Orbit 3, 2008, dual counter-rotating rotors w/ 3 carbon fiber spokes each, dynamic balancing via cutouts, 28" swept diameter.
As is usually the case with technical evolution, one starts out with incomplete and / or incorrect understanding of the issues at hand.  Lessons are learned from each generation of hardware and applied to the next.  It takes many iterations and run-hours to reach a high level of refinement.  The Orbit machines are still in the "youthfull technology" stage, but interesting nonetheless. 

With Orbit 1, a major oversight quickly became evident:  "dynamic torque", the tendency of the rotor to prefer a horizontal orientation when the turntable axis is spinning, was major.  The upper motor often couldn't overcome this force, requiring turntable slowdown to initiate rotor spin.  Once 2 axis spin was going, there were strange resonances - some speed combinations were smooth while others shook the machine violently. Although bolted down, carefully balanced and sturdily built, it still seemed like it could shake itself apart.   After some thought, the related issue of "energy transfer" seemed responsible. A spoke when horizontal is moving fast and  posesses much kinetic energy; as that spoke comes towards verticle it must hand-off that kinetic energy to the turntable axis, making it spin faster. This creates an oscillating torque onto the turntable axis which wracks the truss support structure.   A pair of weights at right angles to the spokes (essentially making a 4 spoke system) helped somewhat, but clearly some major changes were needed.

Orbit 2 dealt with the dynamic torque / energy transfer issues in a more logical way.  A custom software program helped figure out the size and position of weights and spokes such that as 1 pair gave up its energy, another pair recieved it.  This helped a lot.  Also, a stronger truss strategy was employed to reduce the growth of vibration.  Although there are still preferred orientations in fast turntable spin, the upper motor can easily overcome them. 

There is one issue that can't be solved with a 1 rotor system: the gyroscopic effect.  As the "ferris wheel" spins, any attempt to rotate it on a turntable results in a severe sideways torque.  (Spin a bicycle wheel in your hands and you'll feel this wierd fact of physics)  So Orbit 2 unavoidably vibrates at turntable speed. 

Orbit 3 attempts to cancel out the gyroscopic effect with a pair of counter-rotating rotors.  It also takes a more refined aproach to dynamic torque:  using rotor cutouts below the longer spokes intead of weights on the shorter ones.  Counter-rotation, however, creates a new issue:  spokes hitting each other.  Spokes flex under the high g-forces in this type of machine.  Despite employing the stiffest material available for these spokes, rigid carbon fiber, spoke-on-spoke hits are still a concern at high speeds. Orbit 3 also has a larger sweep, more powerful motors, a long distance remote control, and an easier breakdown sequence.     
Orbit 1
Orbit 2
Energy Balance
Orbit 3
Energy Balance
Counter-Rotation
Ring Wave
Independent off-center sencondary axes
A close relative: Ring Wave
This machine can be thought of as taking the 2 secondary "ferris wheel" axes of Orbit 3 and moving them outward.  These axes are independently powered.

Ring wave (described in more detail here) produces interesting patterns, but produces violent dynamic behavior compared to the centered axis Orbit machines.  It also has a lot of inertia on the main axis, so it takes a long time to slow down, and has potential to do "hammer damage", so it must be kept well away from spectators.
works of  Carl C Pisaturo