I made a comparison.
Shown are keys from pivot point to front.
All scaled to same size.
This is not very scientific and unfortunately not all have the black key. So the fallboard position can only be estimated.
However it can be seen that Kawai RM3 has the shortest Key lever arm and that the Kawai Upright is closer to the grand action than the Kawai RM3 action.
So the RM3 must be compared -if this criteria is used- to a rather simple and short Upright action and not to a Grand action. Even the comparison to a Kawai Upright or Seiler Upright would be a bad match.
I did the scaling by sense of proportion, it is not absolutely accurate. Eyeballs and brain must be used to view the images ;-)
It would be interesting to find Images that allow for accurate numeric classification. Please note the images are handscaled and handdrawn and are meant to show the principle, but are not meant to be 100.0% accurate!
Ever asked yourself, why some people say, keyboard xyz is heavy and others say this same xyz is light?
Be aware, that it doesnt matter where the hammer is. This relationship is always true. It follows directly from geometry and principle of energy conservation. If you can prove this untrue, then you can build a perpetuum mobile and win the Nobel Price and buy a real Kawai or Steinway Grand ;-)
That said, if the playing is fast and the playing technique ballistic, then the dynamic forces are much stronger than the static forces. This rule above is still valid for this case, but other forces might become more important. So it is possible that even some skilled pianists are not aware about this basic relationship. Edit: I added the 200% arrows and these are as accurate as I could do. Yamaha wins, Casio looses. It is however, only a small difference so go into the next musicstore and try out, if this matters to you
90 years experience in piano building are clearly visible.
This compares to a simple Upright action that was built 90 years ago. ;-)
Casio Tri Sensor
Fatar TP40W (NUMA Nero)
Fatar TP 100 LR (Numa Piano)
I can see
it, why their action is so noisy. Some damping material like bitumen or selfhardening foam would be required. This is built like a washing machine, so it must be dampened like this ;-)
Yamaha GH3 NW
Yamaha has -so far I know- the disadvantage, that the hammer cannot move away from the key. This seems to be better with Roland and best with Kawai, because the Kawai Key has more mass inertia.
BTW, just to correct another error of mine, I found out that the Yamaha NW action has a little bit more than wooden decorations, it has an element or core of solid wood inside.
It is not hollow inside. I can however not swear it, it is 2nd hand knowledge.
It is unclear to me if the Yamaha image is accurate, as it is a photoshopped advertising image.
If this image has some perspectivic distortion applied for more impressivity, then the actual key lever arm would be even longer.
It seems to me that the Yamaha GH3 is a little bit longer than the KawaiUpright and is the closest match to the KawaiGrand action, if key-lever length is the criteria.
If you know the Yamaha key, then you know that the pivot point is at the very leftmost end of the key, it stands a little bit over. So, if the image is accurate, then Yamaha clearly has the longest key. And it has this since 1996, when the GH action was created. They have escapement functionality for almost 10 years now and had proportional pedal 15 years ago. Technologically they always where ahead of the others.
@Kawai James: Thanks for the photorealistic image. Exchange done.
To the other repliers: Thanks for the interest. I find this criteria most interesting and important. So I used it. It is clear that there are other criterias, such as bouncing, noise, weight and last not least sound. This criteria also has the big advantage, that it is objectively and easily measurable and comparable. However it is an rather important geometric criteria, I think no piano expert would say something else.