In our mechanical system, we valued a solid, reliable structure that allowed us to focus on fulfilling our goal of playing three octaves rather than on flash and unnecessary complexity. We utilized a series of human-inspired fingers to press keys on the keyboard. We connected the fingers in an offset pattern, so that we could place the servos close enough together to play three octaves of notes, including sharps and flats. The mechanism was built from simple, easily replaced components, which allowed easy scaling from one to three octaves, and opened the possibility of including more in the future.
As shown in the CAD to the left, our mechanical system is made up of a series of servos on a V-shaped mount, each with an arm customized for its position relative to the keyboard. We did calculations to ensure that the arms would strike the keys at approximately the same velocity. The arms and servo mount are made of laser-cut MDF, and the arms have felt glued onto their heads to protect the piano keys. The arms are epoxied to the plastic servo attachments. Finally, the servos are screwed into place on the servo mount. We designed a free-standing servo mount to be placed in front of a keyboard or piano. We made this decision because we wanted to prevent any kind of damage to the keyboard, as per our design goals. Instead, we re-designed the mount so that it is self-supporting and does not need to be held up in any manner when it is playing.
Our main challenge was fitting the servos close enough together so that we are able to play keys adjacent to one another on the keyboard. To solve this, we quickly realized that we would have to offset our servos because the width of their casing was too wide. For a single octave, this problem was not too challenging, and was solved with a single V-shaped arrangement. Adding more octaves, however, was more challenging. Our immediate reaction was to keep a single, much larger V-shaped arrangement. However, this would have forced us to create precariously long arms. We re-considered the design to expand past a single V-shape and redesigned some of the arms so that they would be able to pass over other servos closer to the piano.
Over the course of this project, the design for our mechanical system is what changed the most. When we started, we were very interested in making use a mechanical system called a reciprocating rectilinear actuator, which converts continuous rotational motion to bi-directional linear motion. However, after investing some time into designing this system, we found that they would only work if we spent a significant amount of time making sure the tolerances were perfect on the gears. We decided to re-design using laser-cut arms and servos, to get precise position control.
With this decision, we re-evaluated our goals for the mechanical system and determined that we valued reliability over a more complicated system. This decision, which came reasonably early in the project, allowed us to make our system significantly simpler, more modular, and more easily replicated. Replication was an especially important component, as repication was such a key part of of the project. All of these factors allowed us not only to meet our minimum deliverable - a system capapble of playing a single octave in the key of C major - but also to expand to play three times as many notes.