Uke 2.0
Post date: Jul 17, 2014 3:30:55 AM
I just finished installing the frets in the board, so I've learned something new. Don't break into the fret slots unless absolutely necessary. The installation process causes some minor, but fixable cracks between the fret slot and the led hole. On the next version, the bypass caps can be swung around to the side of the LED. Whatever possessed me to think of a 2.0???
I'm also thinking of putting the processor on the back of the led board. I may also switch to a 9v battery. They're easy to get and allow instant power recharge by swapping cells. That would leave only the display , battery box (they're a stock item) and encoder in the body of the uke. The single board might also allow touch sensors too...
The single board eliminates the wiring between the fretboard and the Arduino circuitry. The consideration is the material being removed from the neck. So far, I've kind of looked at any wood being removed as getting replaced by fiberglass FR4 material. However, to make room for parts on the bottom, more material would have to be removed. The strings apply tension that tends to try to bend the neck. If I consider the location of the central axis of the bend, the material I'm removing is more likely in compression, rather than tension. I think a comparison of the modulus of wood (Mahogany) versus FR4 might indicate how much effect I'm having on the stiffness of the composite structure.
Mahogany modulus: 10.6 GPa
FR4 modulus: 24 GPa
One very interesting consideration (that I haven't bothered worrying about until now) is what happens over temperature. Generically for wood, parallel to the grain, the thermal coefficient of expansion is roughly 3 x 10-6 K−1, and for FR4 , 14×10−6 K−1. So, there is quite a significant difference. The concern is that tension is created in the neck as temperature varies that detunes the strings. That's something that could be compensated by applying a similar layer on the opposite side of the neutral axis or by getting the FR4 as close as possible to the neutral axis. But that will be left for 2.0...Something to model up and evaluate.
I might switch the assembly to be more of a composite structure, that is, a frame around the LEDs with a laminated fretboard. That way there are no pockets to mill, just holes. It would take a little risk out of the milling process. This might help with the above problem too.
The order of assembly thus far looks like:
1. Attach the LED board to the neck of the uke. I used 5 minute epoxy to ensure a good bond and no loose surfaces to vibrate.
2. Attach the frets to the milled fretboard. This was not too hard, but I'm not sure this was best done here. Normally this would go after attaching the fretboard, but given other issues, I wanted to be sure I could still get to the back. By the way, the frets do not cause shorts!
3. Attach the fretboard to the neck.
4. Level out the frets
5. Attach LED lenses
6. Finish LED surfaces
7. Mark out the bridge location
8. Apply finish to uke (do I want the rosette decal? kinda thinking no)
9. Attach the bridge
10. Install tuning pegs
11. String and make adjustments.