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# Rotary Rocking Chair

Can rock and swivel at the same time, and doesn't threaten feet
 (+3, -2) [vote for, against]

This chair has two parts, a "base unit" and a "seating unit". For maximum stability, the base needs to be circular and somewhat volcano-shaped (only smaller, of course). That is, from the circular base a cone rises perhaps a foot (~30cm), and the top of the cone is lopped off and replaced with a shallow spherical depression, not much narrower than the circular base.

The seating unit has ordinary width (the width of an average person, and the width of the base unit is about the same). The length of the seating unit should allow for lounging in this chair. Most important, the backside of this unit must be a "section" of the surface of a sphere, like the outer part of a slice from an orange. We want it to match the curvature of the spherical depression at the top of the base unit, of course. This will allow the seating unit to take any of an infinite number of orientations, relative to the base unit. Note that since the base unit doesn't move, a person standing nearby will not risk getting feet squished, when the seating unit "rocks".

The two meshing spherical surfaces should be quite smooth; let us imagine that we add some oil in-between them, to minimize friction. What happens next depends on the "center of mass" of the seating unit. Gravity will act to orient the seating unit so that its mass is balanced around the center of the base unit. We likely will want to add some strategically located weights, to the seating unit, to cause the natural unoccupied orientation of this chair to be relatively normal (compared to other chairs).
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The positions and masses of the weights should be adjustable, to allow the user to specify the default orientation that best matches personal preference. Especially if that preference changes sometime.
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When someone sits in the chair, the orientation that the seating unit now takes will depend on the center of mass of the person-plus-seating-unit combination. But since a person can move the upper body while seated, so can the combined center of mass be altered. So, leaning back will cause the seating unit to recline somewhat. Leaning forward will orient it to a more upright position.

Alternating the leans, of course, is how one starts to rock the chair. Since friction is minimized and gravity is involved, there will be a natural continuation-of-motion effect, such as happens on a playground swing. Accumulated resonance effects will let Rocking be quite easy, in other words. And of course because of the way the two units fit together, it's possible to do a side-to-side twisting motion, simultaneously with a rocking motion, in this chair. Twisting takes more effort than rocking, though, because gravity won't be involved so much, if at all.

Next, the chair should have armrests that don't interfere with sticking out a leg sideways, so that the occupant can use a foot against the floor to rotate the seating unit. Most of the time such rotations would be done only to orient the chair toward some relevant thing (from TV to dining table, maybe), but sometimes one might simply want to spin. And rock at the same time.

One should be cautious about leaning sideways, while occupying this chair. It will be possible to actually rock sideways, but if one overdoes it, a spill will occur. That would be uncomfortable, but probably not dangerous, since the fall will only be a foot or two.

Variations on this basic design and operating principle are quite possible. The oil could be replaced with maglev technology, for example. The occupant would have to make sure no credit-card magnetic stripes are put at risk, though. :)

 — Vernon, Nov 15 2007

As mentioned in the main text [Vernon, Nov 15 2007]

Papasan chair at Wikipedia http://en.wikipedia.../wiki/Papasan_chair
Similar (?) [phoenix, Nov 16 2007]

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[somehow lands on head but still gives Vernon a croissant]
 — DrCurry, Nov 15 2007

For some reason, I'm imagining a relaxed pipe-smoking Davros rocking in one of these and deciding not to invent daleks after all. [+]
 — pertinax, Nov 16 2007

Perhaps I should add this to the main text, but there's no reason a variant seating unit can't be made that's double-wide, to hold two people. Note that the spherical shape of the back of the seating unit may force some cozying-up to occur, but this depends on how the interior of the seating unit is arranged, relative to the exterior. Consider this comparison of two views-from-above:
//
\\
vs
/|
\|
At left is the exterior curvature, and at right is the interior cushioning, for two people side-by-side. A compromise between those may be optimum, for a rotary rocking love seat.
 — Vernon, Nov 16 2007

 And here I thought the prevalent imminent danger from a traditional rocker was to the wayward tail of a contented domesticated feline or canine that chose to recline nearby.

I'm picturing a seat such as you have described with a post sticking out the bottom. The post is inserted through the hole in the top of the cone base. At the end of the post is a counterweight. Granted, the post cannot be of great length nor can the counterweight be so very large as to make the chair of ridiculous proportions, but it would facilitate the desired rocking effects by lowering the overall centre of gravity relative to the pivot point, without the use of springs and gears. How one could achieve the desired minimization of friction is yet to be determined.

The rotary rocking loveseat concept, however, presents a conundrum - if one was to build it using 2 conical bases in order to prevent fall-out when occupied by an individual user, how would one still have it rotate freely?
 — Canuck, Nov 16 2007

This sounds just like a papasan chair (link), albeit with added lubricant.
 — phoenix, Nov 16 2007

 [Canuck], you are misunderstanding how the rocking works, in this chair. There is NO physical pivot point (it is the imaginary center of the sphere that a bunch of these seating units could make if collected together). To see that more clearly, hold your hand palm-upward, so the curve of your palm can support an orange. If you rotate the orange in any/all directions, its pivot point is its center, not any place on its outside. And the love-seat version should simply have a larger single base unit.

[phoenix], I agree that there are some similarities to that sort of chair, but there are also more differences than just lubricant. The base unit of that type of chair is hollow, with only a ring of material at the top to support the weight of the seating unit. Here the weight gets distributed better, across the surface of the spherical contact area (makes rocking easier). In that chair, the rough seating unit frame IS the basic seating unit, with cushioning added. It relies on friction to hold the seating unit in some position, relative to the base unit. This chair requires the back of the unit to be smooth for enhancing the allowing motion to occur; therefore it needs weights for defining an initial orientation. (I'm going to modify the main text to allow adjustments of those weights.) And that seating unit resembles a piece of a sphere sliced by a "chord", more than it resembles an orange-slice; that's why this one can have armrests, while that one doesn't (and why a spill can happen if you rock sideways). Only the two-person version of this chair might resemble a chord-slice, and maybe not even then.
 — Vernon, Nov 16 2007

xaviergisz, proposed something similar.
 — 4whom, Nov 16 2007

I can't really figure out how this works. But I don't care, I want one anyway. [+]
 — Noexit, Nov 16 2007

 Thanks for setting me straight. I was thinking in terms of how a traditional rocker is "powered", i.e. the occupant and trying to superimpose that on your chair.

 If you were to minimize the effects of friction to the point where this becomes feasible, wouldn't the occupant of the chair have some problems? For example:

 1. Getting into the chair would seem to be best achieved by either straddling the seat or entering sideways. To try and be seated normally is just begging to be thrown out either the left or right side of the chair.

 2. Adjusting one's seating position would be also be potentially hazardous in that you are dealing with 3 planes of motion - pitch, yaw, and roll.

 3. Unfortunately, exiting the chair is dead simple - roll over and fall out. However I'm having difficulty envisioning how one would make a graceful, controlled exit to a steady standing position.

 And so on. The other questions I have focus on the centre of gravity issue. I understand that the chair's centre of rotation is an abstract point determined by its curvature. When I apply my mass to the curved surface by sitting down, what prevents the chair from always simply aligning itself to bring the new centre of mass to its lowest point, which would be having me laying as near to horizontal as could be achieved? How does this work as a chair with regards to my personal choices for seating angle (eg. if I want to sit upright at a desk or table, or recline to watch TV)? Other than having me constantly shifting my center of mass, how does the chair actually rock?

I have a feeling there's some little thing I'm just not getting here.
 — Canuck, Nov 17 2007

 [Canuck], you have to fairly constantly shift your body position in an ORDINARY rocking chair, to make it keep rocking. The effort here should be no greater than that, if friction between the two units is minimized enough.

 Also, it is likely that while the seating unit may be near-body-length, to allow lounging, probably your feet will extend beyond that length in most constructions of this chair. Good cushioning at that edge of the seating unit would be important for comfort. The purpose would be to help ensure the person-plus-seating-unit center-of-mass can allow a fairly ordinary and mostly vertical position (for the torso) to be maintained. Also, if the adjustable weights were adjustable by the seated person, that could help a lot, too.

I would say that most of the problems you point out can be dealt with by simply getting into the chair slowly, rather than quickly.
 — Vernon, Nov 17 2007

 In my experience, in a traditional rocker you push it back with your foot, or feet, then gravity does the rest.

It seems to me that learning how to use this chair might be somewhat like learning how to ride a bicycle, for someone like me anyway.
 — Canuck, Nov 18 2007

[Canuck], put a little kid in an ordinary rocking chair, and the kid can rock the chair without feet touching the floor. For an adult, just think of rocking, in THIS chair, as good abdominal exercise.
 — Vernon, Nov 19 2007

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