Re: Automatic Wheelchair Turntable

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 30 Sep 2005 10:16:02 GMT, nobody@xxxxxxxxxxxx (Dave Houston) wrote
in message  <433d0f5a.142744267@xxxxxxxxxxxxx>:

>That's why I suggested bearings under the entire surface. With central
>bearings like a lazy susan, the weight will be applied far outboard of the
>bearing.

Do ideas become better by repetition?

Physics 101: the force on the lazy susan bearing ("weight") will be applied
_on_ the bearings regardless of how "far outboard of the bearing " the
wheels of the chair sit on the rigid platform affixed to the bearing.

As long as the lazy susan (a thrust bearing) has adequate vertical load
capacity, and the lateral force is negligible (which it is), the diameter of
the lazy susan becomes important only if the vertical force cannot be made
symmetric. An imbalance places the force on fewer bearings.

Having bearings "under the entire surface" makes the construction much more
complicated and would as a practical matter would increase friction. What
would be the surfaces on which "bearings under the entire surface" would
roll? I suppose one could arrange them in a circle with a mechanism to hold
them captive and provide a surface both top and bottom for them to roll on
that itself would be mounted to flanges that could be attached to the fixed
and rotating structures. I wonder what we would call this newly invented
device?

If there were "bearings under the entire surface", what would be their
geometry of their traces on the rotating platform if not a circle?   If it
is a circle, why not use a "lazy susan". If one did have multiple concentric
lazy susans, how would that help in any way in the case that weight was
transferred to the outermost bearing of the outermost lazy susan in the case
of weight imbalance? (It wouldn't).

Marc
Marc_F_Hult
www.ECOntrol.org