Initial Phase
At the beginning, we had to decide on a way to strum the strings. We considered 2 main options. Firstly, an arm connected directly to a motor that would strum the string as the motor rotated, and secondly, an arm that would be connected to a conveyor track suspended over the lyre strings, which would be revolved by motors on either end of the lyre. After some discussion, we decided on the former option.
Using some spare parts that were lying around the lab, we confirmed that this concept would be able to create a decent sound while strumming the lyre. Thus, we decided to proceed to design and construct the machine around this type of arm.
Prototype
After making some measurements, we designed the prototype of the machine with the intention to play 10 strings on a lyre. With our design, it will be highly difficult to play all the strings on the lyre. Thus, we got a 19-string lyre and removed the intermediate strings, to create a 10-string lyre.
We decided to construct the frame out of 2020 aluminum extrusions, as they were not too bulky and easy to obtain compatible brackets for.
For the motors, we needed a motor that was small enough to be able to fit at least 5 in a row on a 30cm length extrusion, while at the same time having enough torque to strum the strings. Eventually, we decided on using NEMA 17 stepper motors to drive the arms.
In order to mount the motors to the frame, we initially designed a bracket to be printed and used to connect the NEMA 17 mounting bracket to the aluminum extension.
For the arms, we decided to use guitar picks as the strumming point due to the similarity between guitar and lyre strings. An arm was designed that would be secured to the motor pivot using nuts and bolts, and would hold a guitar pick in a slit on the end.
For our prototype, we made a rough setup with 10 motors that was able to play a 10-string lyre.
Final Product
After our success with the 10-string lyre, we felt a little more ambitious and decided to upgrade our design to accommodate 12 strings. As we still wanted roughly equal spacing between strings, we decided to get a 24-string lyre and remove alternate strings in the same way we did for the 19-string lyre.
From the prototype to the final product, we made a few more changes.
- With more strings to strum, some motors had to be positioned far from the center position, which meant that the 8.5cm long arms that were used thus far could not reach the lyre strings. To remedy that, some arm variations that were 9cm to 9.5cm long were printed so all the motor arms could reach and strum their assigned strings.
2. We decided to do away with the mounting bracket, and instead mount the motor bracket directly to the aluminum extrusion. While we initially avoided this due to the labor involved and the difficulty in demounting the motor brackets once mounted, we decided to go forward with it as our design was mostly finalized by this point.
3. We replaced the aluminum extrusions of the frame with ones of specific lengths, by cutting those of excessive length down to size, to reduce the overall bulkiness of the frame.
4. Screws that act as stoppers were added in order to add homing to the motors so that they will be able to play songs without having to be manually set to their starting positions.
5. A box was added at the top of the machine to contain all the motor drivers and Arduino circuitry.
