Virtual Capstan

[Bill Ballard]

At 12:09 PM -0400 6/21/03, Mark Davidson wrote:
>This was my initial reaction.  You do less work at the front
>of the key but the same amount at the back of the key.  How's that possible?
>Yet he's got the experimental data to show it works.

The data you refer to is static, and is merely a reading of how the 
gravitational pull on each side of the key is balanced across the 
fulcrum.

>I think the answer lies in that fact that the magnets, like a spring, have
>stored energy that is released as the wippen and key move apart 
>which does some of the
>work. This energy is stored again as the parts move back together. 
>It wouldn't
>work if the distance between the parts were not changing.

I don't know how it works for magnets, but for springs, barely 8% of 
of stored force is relieved at the top of the wippen's swing. The way 
to release 100% of the stored energy is to unhook the spring. With 
magnets, the force doesn't exist (excuse me, it doesn't become strong 
enough to be noticeable) until you bring like poles of two magnetic 
fields close enough. That doesn't sound like a force-storing system 
to me. Stored energy is at work however with inertia and gravity, as 
well as deformation of springs.

As far as the wippen and key moving separately (de-coupling), that 
needs to be studied.

At 7:38 PM +0200 6/21/03, Richard Brekne wrote:
>Ron Nossaman wrote:
>
>>  >Then put a 45 gram weight on the front of the key and begin to screw down
>>  >the whippen magnet so that it gets closer and closer to the key. At some
>>  >point the key will just start to move on its own.
>>
>>  And as it does, the distance between the magnets increases and the touch
>>  weight does too as the magnet repulsion lessens. The down pressure from the
>>  repulsion on the back of the key lessens too, but to a lesser degree
>>  because of the leverage differences.
>
>Actually, the distance between the magnets is so stable that I dont think you
>can notice this with conventional UW/DW measurements. Tho there is a slight
>difference in the amount of vertical rise in the whippen at this 
>point compared
>to the key at this point to be sure. In anycase...it doesnt affect the motion
>characteristics of either measurement noticebly.


Let's be clear about this, guys. When, Ric, you say that at some 
point the key will start to move on its own, I'm assuming that the 
key is moving downwards, meaning that the magnetic repulsion has 
reduced the load on the "bricks'n'mortar" capstan to the point where 
the FW plus the 45g deadweight can overcome the DW. At that point, 
with the front half of the key moving downwards, the back half with 
its "two" capstans and their load would be moving upwards. This is 
not where I would expect to find the gap between magnets expanding. 
Actually, I would expect to find that until a certain point is 
velocity, gravity and the magnetic repulsion would have no trouble 
finding a stable balance.

If, Ron, you're thinking of motion of the key which might occurs as 
the repulsive force grows strong enough to force the key down into 
the backrail cloth (showing an upwards motion which a dial indicator 
could read), that may be true. However, as the increasing repulsion 
tries to relieve itself, at a certian point it will have out-run the 
squash in the backrail felt and balance rail punchings, and at which 
the repulsion will have a far easier time pushing upwards on the 
wippen (instead of downward on the key). That's the point at which 
Ric gets the signal that UW has been overcome.

Let me know if there's something I have to write on the blackboard 100 times.

Bill Ballard RPT
NH Chapter, P.T.G.

"When writing a mental note, first procure a mental piece of paper"
     ............mental graffitti
+++++++++++++++++++++