Keys and MOI - wipp assist

[Fred Sturm]

	Thanks for the feedback, John. I'm just wondering how such a thing as a 
wipp assist spring fits into calculations. It seems to me the wipp assist 
is very similar to the Fazioli magnetic underkey whatsits. Both are fairly 
static sources of energy (the wipp assist spring de-compresses very little, 
hence its available energy remains fairly constant throughout an action 
event. As does the force of the underkey magnets, since the distance 
doesn't contract that much).
	Since moi is perceived at the key as resistance to the force of the finger 
which is trying to accelerate, and since in the case of both the spring and 
the magnet, force is being added to the system, it would seem that there 
might be an effect that would "feel like" reduction in moi. But maybe not. 
The issue is whether these two means of reducing mass as measured at the 
key have an effect at all levels of acceleration. It's the really fast 
acceleration (hard blow, fortissimo playing) where moi is really felt (as 
others have pointed out earlier, in comparison to pianissimo playing which 
is proportional more to simple balance weight). Or so I surmise. I guess it 
comes down to, "Does the heavier hammer compensated for by the wipp assist 
feel heavier on faster/louder blows? Same question with magnets 
substituted?" And how does one calculate what effect forces like these have 
on weights and levers and inertia?
Regards,
Fred Sturm
University of New Mexico
	


--On Tuesday, January 6, 2004 2:21 PM -0500 John Hartman 
[link redacted at request of site owner - Jul 25, 2015]

> Fred Sturm wrote:
>>
>>     I guess my main question is, "Is the moi of the hammer assembly, as
>> perceived from the key, reduced by the engagement of the spring?" Since
>> the stored energy is always present, the energy required to accelerate
>> the hammer assembly mass from the front of the key is always reduced. So
>> does that, in effect, reduce the moi of the hammer assembly mass? Or how
>> does the spring enter into the picture in engineering terms?
>>
>
> Fred,
>
> I would say no, the spring does not change the MOI of the hammer or how
> it is felt at the fey. When the action is at rest the spring has
> potential energy. When the key is depressed the energy is used to help
> move the action. When the action returns to rest the spring is compressed
> and it stores the energy for latter use.
>
> I suspect the drawback of using the springs is the potential for creating
> undue harmonic motion in the action. With too much spring tension the
> action would take a wile to come to rest. There would be a lot more dance
> to the keys.
>
>
> John Hartman RPT
>
> John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
> Rebuilding Steinway and Mason & Hamlin
> Grand Pianos Since 1979
>
> Piano Technicians Journal
> Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]
>
>
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