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# Multi-ball Spherical Motor

Many small ball magnets spin in unison to counterrotate a large ball.
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Spherical motors typically use large numbers of electromagnetic coils and have no gearing to increase torque. This makes them heavy and expensive.

This concept uses only three electromagnet coils and uses spherical "gearing" to provide lots of torque. The central ball is made of high traction plastic. Around it are many small spherical rare earth magnets coated with high traction plastic. Each of these magnets is constrained on five sides by low friction ball bearings. The sixth side is the main ball.

Thus, there's an inner sphere surrounded by many magnetic balls. Outside the entire arrangement, you have three perpendicular magnetic coils. By adjusting the current in these three magnetic coils, it's possible to create a magnetic field along any axis.

All of the magnetic balls align parallel to this magnetic field. By rotating this axis in a great circle, the magnetic balls all rotate in unison. This causes the central ball to counterrotate in the opposite direction. However, mechanical advantage of the ratio of the sphere diameters means that the central ball rotates much slower, with more torque.

Interestingly, you can use the magnetic field to "coast" in one direction. For example, if you line up the magnetic field vertically, then the magnetic balls can freely rotate around the vertical axis. If you line up the magnetic field East-West, then the balls can freely roll North-South.

This motor is suitable for use either as an all-direction spherical wheel, or a 3-axis robotic ball joint.

 — IJK, Mar 20 2007

[MaxwellBuchanan, Dec 22 2018]

Spherical motors??
 — notexactly, Dec 19 2018

Anno added on 20/12/2018, possibly some variant of Mayan Long Count?
 — not_morrison_rm, Dec 20 2018

It's a shame this one was overlooked. I quite like the idea, I think. One thing I'm not sure of is what spherical motors can be used for - with all those degrees of freedom, how do you couple anything to it? I can see it working as a sort of spherical wheel, though. Also, <link> shows a spherical motor in action. Quite neat!
 — MaxwellBuchanan, Dec 22 2018

Could be good for a reaction wheel, I guess.
 — notexactly, Dec 30 2018

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