Re: [Phys-l] Interesting complex machines

[Brian Whatcott <betwys1@sbcglobal.net>]

Dwight K. Souder wrote:
> Greetings everyone.  In my physics classes, we've been going over simple
> and complex machines.  I've given the assignment for the students to
> find a "simple" complex machine, identify the simple machines within the
> complex machine, and build a working model of the device.  Examples of
> this include transferring rotational motion into linear motion as seen
> here:  http://www.youtube.com/watch?v=wpO8_RRp_Z8 or
> http://www.youtube.com/watch?v=8dR38uQN74c, or transferring rotational
> motion into a "walking motion" as seen here:
> http://www.youtube.com/watch?v=CufN43By79s.
>  
> We've also taken apart several mechanical clocks, door mechanisms,
> locks, etc. to study the mechanisms at work.  The students love it.  I
> even have one group of students who are working on a pendulum driven
> clock that is primarily made of old CDs.
>  
> One of my students came to me and she's trying to find the mechanism
> that allows for a small rotation in one direction, but then a larger
> rotation in the opposite direction.  She's presented several theories of
> what they may be, but none of them have worked.  It has both of us
> stumped.  She found a video that shows it at:
> http://www.youtube.com/watch?v=XI9Z0svRisU .  If you watch the wheel in
> the upper right, as the spiral wheel begins to rotate in the opposite
> direction, something is triggered to allow the upper right wheel to back
> up a little and then make a larger rotation in the opposite direction.
> These kinetic sculptures are powered only by constant force springs and
> are entirely mechanical.  They are amazing to watch.
>  
> Does anyone know how such a mechanism may be put together to prevent
> rotation in one direction (ie. clockwise), until a small amount of
> opposite rotation is generated (ie. counterclockwise), that would allow
> for the primary rotation to occur (ie. clockwise)?  I love it when a
> student has me stumped.  :-)  Any help would be greatly
> appreciated...from both of us.  (hahaha)
>  
>  
> Mr. Souder
This is a pretty kinetic sculpture. It seems to have a clock mainspring 
(ot two?)
in base and reduction belt wheels driving two escapement wheels of a sort.
The drive seems to be pass from them through very soft concentric 
helical springs
on the axles of the final wheels.
Soft springs on an axle can act as a mechanical diode,  in that driving 
the spring
in the direction of tightening locks it on the shaft, while  the other 
direction allows
a much longer arc. The mechanical details of the escapement in the upper
right wheel hubs are not clear to me.

Brian W