Newton, Thanks for confirming the definition of up weight and down weight for me. Yes, I am in the very early stages of developing an automated device to measure these parameters. Key to this design is a digital scale. I have been unable to find anything ready-made, so I am trying to make one from scratch. As for a motorized "thumper", how about starting with one of those massage units that normally strap on the back of your hand? If the cushioned padding were removed and the unit were fastened securely to the keybed, it would induce a nice steady vibration that might be just what is needed to break static friction. You also asked about measuring key inertia. What is needed in principle is a key stroke that is as hard as you dare, the limiting factor being the potential for damaging the action. With a very hard key stroke, the reaction force due to inertia would swamp the force due to friction. (And if you already had done the up/down weight measurement, you could even subtract out that little difference.) In practice, the way I would measure action inertia would be to strike the key with an apparatus that contacted the key through a spring, and then bounced back up. If the inertia of the apparatus were equal to that of the action, then all of the momentum of the striking apparatus would be transferred to the action, just like in those swinging metal balls. But if the inertia of the striking apparatus is less than that of the action, then the striking apparatus will rebound away from the key. If you measure how high it rebounds, you will be able to compute the action inertia. Just make sure that rebounding happens before the hammer strikes the string, or else the measurement will be invalid. To make sure that the striking apparatus always rebounds, make the inertia of the striking apparatus less than the lowest expected action inertia. Perhaps you could use several different strikers - high inertia ones for measuring bass action and low inertia ones for measuring treble action inertia. So we have reduced the problem of measuring action inertia to the measurement of the rebound height of a springy striker. And the way I would measure that is to time the period between the first strike and the second one and use the formula for free fall in gravity to relate the time to the rebound height. The striking event is easy to detect with a piezo accelerometer in the striker (essentially, an old- fashioned phonograph pickup). -Bob Scott Ann Arbor, Michigan
This PTG archive page provided courtesy of Moy Piano Service, LLC