Posting the video about the parallelogram linkage of the keys. Will just leave it in this thread instead of starting a new one as its not really as complex as the other topics.
In summary, regular pianos feature a simple lever for their keys - which makes playing the same note at constant volume require different amounts of force based on where you play on the key (playing along the back requires ~2x more force and has 1/2 the travel distance than playing along the front). In the Janko piano this is further worsened by the keys being longer, so either the lever needs to be longer as well or the player needs to accept 3x or more difference between the front and back rows.
To solve this a parallelogram linkage is used to ensure that the key has a consistent 10mm of dip throughout the entire key - no matter if you play on the front row or the back row.
PS: just to clarify; the difference in key dip along the length of the key on a classical piano isnt exactly a 'problem' for players - you pretty much never think about pressing 'harder' when playing along the backs of the keys - you just do it subconsciously. However as anyone who played on a cheaper synth keyboards with like 1mm key-dip along the backs of the keys can tell you there are limits here - 2x difference is kind of the sweet spot, and on a Janko keyboard with its longer keys it becomes harder and harder to stay within that sweet spot for all rows - hence the parallelogram approach.
Plus, having consistent key dip is kind of nice in and of itself. Almost like taking off a weight you've been carrying for so long you no longer notice its there.
