Re: Automatic Wheelchair Turntable

["Robert L Bass" <robertlbass@xxxxxxxxxxx>]

"Marc F Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:tgdqj1hmcnf28bcn6ir2n4d1ti17hnnmnl@xxxxxxxxxx
> 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.

I suspect Mr. Houston may be concerned that the lazy susan (plywood has been
suggested for the disc) will flex under the weight of the chair and
occupant.  That might merit considering outer and perhaps mid-circle
bearings.  Certainly there is no need for bearings under the entire surface.
That could be accomplished if the disk sat in the middle of a plate covered
with ball bearings but it seems like a really bad idea.

My concern with the whole bearings-under-plywood idea is that the plywood
would quickly become rutted, increasing drag and eventually binding.

I think the best suggestion yet was to back in and drive out forward.
Backing down a ramp would be more hazardous than backing up, presenting a
serious chance of tipping over given the geometry of wheelchairs and
scooters (the front axle is usually more forward of the occupant than the
rear axle).

--

Regards,
Robert L Bass

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