# Is it possible to have a self-balancing system?

I am trying to create a machine that moves on two points (Wheels or legs). Because of the extremely difficult nature of perfectly balancing the parts, I am wondering is there any way to create a mechanical mechanism to balance it. I know that it can be done with many different electric circuits, but I am wondering is it even theoretically possible to create such a system? And if it's possible, does anyone know of any systems that do that?

P.S. Could someone retag this appropriately? I'm new to this SE, and I'm not sure how to tag it.

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This is probably covered by the segway patent, but this was the major hurdle. –  Ron Maimon May 15 '12 at 22:29
Yes, but I don't want to use any type of computer. –  J. Walker May 15 '12 at 22:48
You could do it with a mechanical contraption, which has a bunch of gyroscopes connected to mechanical motorized weight-movers, but I don't see why you don't want a computer--- the result will be equivalent. –  Ron Maimon May 16 '12 at 1:23
Look here as well: physics.stackexchange.com/questions/1875/… –  troyaner May 16 '12 at 18:19
Are gyroscopes allowed? –  user1631 May 16 '12 at 20:47

A passive machine on a surface (of gravitationaly attracting sphere = ideal Earth) cannot be in a stable or meta stable state with only two supports.

A di-pod cannot span an area, in a way that it's center of gravity stays within if tilted.

unlike the doll below, which has always a projected area around it's point of support under it's center of gravity - a two-legged system spans only a line, which is easy to cross.

Self-balancing system should revert to it's state after a small (and to be defined, in the example below it would be $x_a - x_b$) dicsplacement. In terms of a potential this is the case for stable and meta-stable states. In the picture the state of your system is related to potential (y-axis), and some abstract position is at the x-axis: e.g. Your system is staying "upright" at $x_a$, it will go back to $x_a$ if pushed with less effort than $\Delta U$, and will be "falling down" untill it reaches next stable position at $x_c$ "lying down"

Addendum: A bag hook could be considered stable virtually having only one support, but it's not an option, for a) moving machine b) on a surface

Upon further reflection - the hook is actually hanging on a table, which has at least three supports itself.

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