Xavier the xylophone robot

Post your comments on the youtube page:
https://www.youtube.com/watch?v=xCa3EzTXzd0
Project performed in 2017, P2I6 mécatronique at INSA Lyon , France
12 students

Xylophone demonstration with the robotic orchestra

Manufacturing and Multi-Modal Tuning of Xylophone Bars

We use 40x10 mm² aluminium to manufacture the xylophone bars. The material is AU4G1 (Aluminum 2024 for USA).
Prismatic bars vibration is anharmonic: f2/f1=2.76 and f3/f1=5.40
We need to remove material at the center of the bar to have harmonic bars.
We want to have: f2/f1=4 and f3/f1=9.8
This is the most common tuning for Marimba. The tuning for xylophone is different.

Step 1:

Xylophone bars shape calculation with Matlab and Zhao inspired code

Graphical result for 10 mm thick bars. 19 bars calculated from C5.

Here is the modified code
Here is the original Zhao code
The code is useful for Step 1 and step 6.
The code is very efficient with aluminium because the physical properties of aluminium is very well controled.
The code exports the shape as csv

The code is a bit messy . Have a look to Rich code on Supermediocree; Mayb it's easier to understand....

Step 2:

csv import to the CAD software Solidedge



Step 3:

Shape manufacturing with CNC. The CNC program as generated with NXcam from the Solidedge CAD software.

Step 4:

Drill hole with salt method

Step: 5 Experimental frequencies analysis


We use the following applications:

Da tuner:(Android)



Very good for fundemental but not harmonic
It is possible to hit aluminium bar near the node to have the 1st harmonic intensity higher than the fundamental.
Here is a demonstration:

FFT Spectrum:(Android)


Good for quick harmonic vizualisation but the sample size are too small. The harmonics frequency precision is not good enought. It can't be used for fine tuning.
Here can be seen the fondamental (522 Hz) and first harmonic (2085 Hz)

Audacity:(Windows/Mac/Linux)


It is possible to specify a 32768 sample size and the harmonics can be seen with a very prcecise frequency.

A quicker method is to use Datuner and hit the bar near the hole to have the first harmonic frequency instead of the fondamental.

Step 6:

Fine tuning position calculation with matlab. White columns are the frequencies after milling and before tuning.
Blues columns is the position (pos) and the depth (depth) where material must be removed.

Theorical frequency Measured Offset % File
Note f0 f1 f2 f0 f1 f2 f0 f1 f2 f0 f1 f2 pos depth
C5 523,3 2093,2 5128,34 525 2112 5147 1,7 18,8 18,66 0,32 0,9 0,36 76,47 0,79

554,42 2217,67 5433,29 558 2240 5426 3,58 22,33 -7,29 0,65 1,01 -0,13 82,54 0,42
D5 587,38 2349,54 5756,37 592 2394 5729 4,62 44,46 -27,37 0,79 1,89 -0,48 74,18 0,94

622,31 2489,25 6098,66 628 2513 6055 5,69 23,75 -43,66 0,91 0,95 -0,72 81,16 0,31
E5 659,32 2637,27 6461,3 664 2661 6407 4,68 23,73 -54,3 0,71 0,9 -0,84 78,22 0,34
F5 698,52 2794,09 6845,51 721 2862 6808 22,48 67,91 -37,51 3,22 2,43 -0,55 77,83 0,45

740,06 2960,23 7252,57 771 3048 7210 30,94 87,77 -42,57 4,18 2,96 -0,59 76,21 0,5
G5 784,06 3136,26 7683,83 818 3231 7638 33,94 94,74 -45,83 4,33 3,02 -0,6 74,04 0,51

830,69 3322,75 8140,73 869 3431 8333 38,31 108,25 192,27 4,61 3,26 2,36 71,93 0,52
A5 880,08 3520,33 8624,81 905 3588 8625 24,92 67,67 0,19 2,83 1,92 0 70,43 0,36

932,41 3729,66 9137,66 963 3812 8945 30,59 82,34 -192,66 3,28 2,21 -2,11 68,42 0,39
B5 987,86 3951,44 9681,02 1014 4016 9427 26,14 64,56 -254,02 2,65 1,63 -2,62 66,48 0,31
C6 1046,6 4186,4 10256,68 1078 4252 9628 31,4 65,6 -628,68 3 1,57 -6,13 65,59 0,32


Step 7

The metal is removed at File "pos" acording to the matlab calculated table with a half round file. The depth is controled with Datuner on f0 because too difficult du measure with a micrometer.
When f0 is tune on the theorical frequency, f1 and f2 are tuned too!

Half round file

Resonators


Cut view of resonnators: Resonnator are made with a Ø40 mm PVC pipe.  Stoppers in PVC(blue) are CNC machined. A O ring (not shown on the figure) allows an easy adjustment.

Resonator tuning

The resonator tuning was made with an android phone with Audio Test Tone Generator:


We play a sine frequency at 1 cm from the resonnator. We adjust the stoppers position to the theorical frequency of the bar (the bars were not ready at this step of manufacturing).

Electronic control with arduino and midi shield




Here are the sources for the components

Arduino mega (for the 13x mosfet control solenoid):
https://store.arduino.cc/usa/arduino-mega-2560-rev3
Arduino yun (for the wifi control - optional)
https://store.arduino.cc/usa/arduino-yun
A cheaper option would be ESP8266
Midi shield (for midi interface) DEV-12898
https://www.sparkfun.com/products/12898
Mosfet STP36NF06L
http://fr.rs-online.com/web/p/transistors-mosfet/4865671/
Solenoid LS2924BD: 12V  9W
https://www.gotronic.fr/art-solenoide-12-vcc-ls2924bd-11904.htm

Link
Supermediocre xylophone building
http://supermediocre.org/index.php/rich/richs-projects/xylophone-project/

Post your comments on the youtube page:

https://www.youtube.com/watch?v=xCa3EzTXzd0