Research project on the development
of new tools for musical expression at the University College Ghent
School of Arts
an automated set of bronze tines
2013 - 2014
Rods clamped on one side and free to vibrate at the other side are the acoustical
base of quite many musical instruments and sound installations: reed organs,
mouth organs, bandoneon, music boxes with a comb, nail violin, toy piano, Fender-Rhodes
piano, Waterphones, Harry Bertoia's installations, African lamellophones, clock
gongs to name just a few. Two classes of instruments using this sound source
should be distinguished: instruments that only use the fundamental resonant
tone (reed organs, Fender-Rhodes, music boxes) and that are always considered
pitched instruments and at the other hand those that use the broad spectrum
of overtones these rods can generate, when tuned to very low fundamental resonant
frequencies (clocks, Waterphone, toy piano...). The fundamental resonant frequency
of these rods is inversely proportional to the square of the length of the rod:
With: f= frequency in
Hz, L= length of the rod, k=diameter of the rod, Q= modulus of elasticity, r=
density of the material. (Olson, p.76)
The <Rodo> robot was designed to be either an extension or a generalization
of the toy piano robot <Toypi>. Just like in the toy piano, the sounds
all stem from massive rods clamped at one end in a solid cast iron bar. We started
the project, as the automation of the small instrument was very successful and
appeared to have many more sonic possibilities than we grasped at the start.
So we thought of rescaling the design such that the range would extend much
lower and the maximum sound level quite a bit higher. At the same time, we aimed
at making the instrument a lot more sturdy than the toy instrument, that needed
all too many repairs because the tines broke very easily on very fast note-repetition
rates. Also quite some new features were added in this design: individual dampers,
an e-drive mechanism and a set of sensors to allow gesture interactive activation
and playing modes.
We started off by doing experiments on different metals and alloys for the
tines: martensic stainless steel, hardened spring steel, brass, aluminum, phosfor-bronze,
aluminum-bronze. We even experimented with some non metals such as bamboo, glass,
carbon-fibre. Those experiments made us drop the nonmetals very fast as the
sound was too weak or the rods too fragile. Obviously the evaluation of sonic
quality has to remain a quite subjective issue, since there is no standard to
compare to as we are designing a new instrument. After all these experiments
were performed we decided to go for the aluminum-bronze alloy. These rods produce
a very rich tone, though not as brilliant and loud as spring steel rods. As
we couldn't get beryllium copper (after the properties, it ought to be the perfect
material here) nor phosphor bronze (CuSn8) ,we cannot judge on these promising
alloys. In the design of <Rodo> we took into account the possibility for
tuning and adaptation to different tuning systems. To allow this, set screws
are used to fix the vibrating length of the tone rods. This arrangement makes
it possible to exchange the rods for other sets, as long as the diameter is
8 mm. By default the tuning is chromatic, equal temperament. Due to the high
inharmonicity of vibrating bars clamped at one end, it is perfectly possible
to consider the instrument as 'non-pitched' in the context of orchestra compositions
conceived for our robots. In this respect, the instrument would sound like a
set of gongs.
The acoustics of rods clamped at one end, after the theory books (Rayleigh,V1,p.278;
Talukdar) allow us to predict the frequency of the overtones.
The literature on the subject doesn't give any values for higher overtones than
f5. Also, different authors do not seem to agree on the exact values of the factors.
The factors derived from theoretical calculus, generally simplify the problem
by neglecting the torsional forces occurring in vibrating rods, only considering
lateral vibration. So, these factors can only be used as guidelines and experiments
were necessary to obtain exact results.
One would expect that the perceived pitch of a struck and clamped rod would
correspond to at least one of these overtones, however -at least for the rods
we selected- this is not the case. In the table below we give the measured frequencies
of a single bronze rod, 8mm in diameter and cut to a length of 961 mm. (An extra
length of 20 mm serves for clamping and thus can be considered acoustically
dead). The perceived pitch of this bar was C#3 raised 20 cents (139.45 Hz),
yet this pitch was not found back under forced resonance conditions::
||=MM296, checked by comparison to a metronome set to MM150
||reference tone used for best match with calculated spectrum
||this corresponds to the octave above the perceived pitch (139.45 Hz)
Measurements were performed under forced excitation using a transducer driven
by a Thurlby Thandar TG1006 DDS function generator with a 6 digit frequency
readout. Resonance's were determined by very slowly sweeping the sine wave frequency
and fine tuning to find the peeks in amplitude. When we tried to make the rod
resonate to the perceived pitch of 139.45 Hz, it clearly responded with the
pitch found in the table for f4. The conclusion is that our ear adds a 'missing
fundamental' here. This is not something novel, as similar phenomena have been
described with regard to the perceived pitches of tubular bells.
To conclude our measurements on the test rod, we tried to excite it with a
bow and could find all overtones from f2 to f9 back, be it sometimes after quite
some attempts as it seems difficult to predict the pitch one will get when bowing.
Starting from the measurements and experimental data obtained, we designed
a small computer program to calculate all 31 rods based on a perceived pitch
range from C3 (midi note 48) to F#5 (midi note 78) for equal temperament and
a basic tuning to A=440 Hz..
The negative fractional midi note numbers in the note0 column (giving the fundamental
frequency of the rods) are colored brown, as these cannot be properly expressed
in MIDI. Beyond that, it will be clear that they are absolutely inaudible. To
measure their frequency, a calibrated stroboscope can be used. The notes given
as overtones are notated as fractional midi, the integer part being the midi
note and the fractional part the fraction in cents. Note that the (nearly) fifth
intervals between the notes 4 and 5 are the cause of our perception of a missing
fundamental, heard as f4 / 2.
To strike the tines, we decided to use Kuhnke thrust type solenoids with conical
face armatures. Type HM157 has an armature weighting only 8 g. The nominal voltage
for 100% duty cycle is 24 V, but at that voltage the attack time is 34 ms for
a traject of 5 mm. The data sheet specifies:
The DC resistance of the coil is 206 Ohms. We decided to design the robot for
operation on 60 V and thus the duty cycle should be restricted to 15%. Thus
the maximum note repetition speed at full power should be brought down from
the theoretical maximum of 50 strokes a second to ca. 15 strokes a second. Power
supply requirements can now be derived from these data: we have 31 solenoids
and thus the required power becomes: 18 W * 31 * 0.15 = 84 W. In order to stay
on the safe side, a 48 V ac transformer rated at 100 VA should do the job. After
rectification and smoothing, this will give us a dc voltage of ca. 65 V without
load, going down to 48 V al full load. By raising the voltage, we can improve
the attack time considerably as shown, but one should keep in mind that the
fall back time is limited by the force of gravity. When we calculate this for
a fall trajectory of 5 mm ( t = SQR(0.005/4.9) we get 32 ms. Thus the fastest
full up-down cycle would take 40 ms, leading to a fastest possible repetition
speed of 25 Hz. However, in practice when driven much faster than these repetition
speeds, it still works fine but the anchors will not fully fall back between
strokes. As a consequence, the amplitude of the produced sound will decrease.
The mass of the longest tine being ca. 400 g entails that the striking force
for a good excitation ought to be between 0.39 N and 0.78 N. These values will
be reached with midi velocity values around 80.
An extra and new feature of the <Rodo> design, as compared to <Toypi>
is the electromagnetic feedback driver mechanism. To this end we mounted a powerful
(100 W) electromagnet very close (leaving just an air gap less than 0.1 mm)
to and underneath the cast iron bar. This electromagnet is driven by a high
voltage amplifier whose input comes from an ARM processor. The input for the
driver can be either a signal picked up with a piezo transducer from the soundboard
filtered and processed by the ARM controller, or a drive signal under midi-controll.
This mechanism enables bowed and sustained sounds to be produced from this instrument.
Rodo can sound very much like a bowed string instrument in this mode, although
sound build-up is rather slow due to the inertia of the mass of the rod assembly.
An improvement over the <Toypi> robot certainly consists in the damping
possibilities offered here. Each rod has an individual damper mounted exactly
above the point of excitation. The duration of the contact between the felt
covered damper and the tone rod can be controlled with the release value of
the note-off command. A sustain controller (#64) is implemented, to disable
the damping functionality completely. A controller is used to set the default
damper-contact-time for note-off commands with release parameter 0. This was
done for user friendliness, as most commercial sequencers do not offer the user
the possibility to send note-off with release values, although these are part
of the standard midi specification.
For the damper mechanism, we went for tubular push type solenoids (Lucas-Ledex
type...). This entailed the use of return springs, calculated such that at rest
their force just keeps the damper and the plunger above the tone rods without
making contact. As the plungers on these tubular solenoids have an open cylindrical
head, we attached 10 mm brass disks to the ends and fitted the return spring
over the plunger. We used the same springs as we had custom made for our
Midi implementation and mapping:
Note off: steers the dampers on the rods, if sustain is switched off. Value
0, makes use the the default damper time set by controller #14. Value 127 keeps
the damper on as long as a note-on is not received. Values between 1 and 126,
control the time the damper felt stays in contact with the rod. Note that it
is possible to play a nice pp by using the dampers as very soft beaters. This
is done by sending only note-off commands with the release value set for the
required velocity in the range 1 to 126.
Note on: The velocity byte steers the force of the strokes. For very fast repetition
rates, low values for velocity should be used.
The lights are mapped on midi notes as follows:
- Note 112 and 113: Blue LED spotlights on the front
- Note 114 and 115: Yellow LED spotlights left and right on the bottom plate
in the back.
- Note 120 and 121: Red LED spotlights to the floor
- Note 124 White LED strip on the beaters
- Note 125 White LED strip on the back side
- Note 126 Red rotating warning light
Note pressure: Steers the repetition frequency of the
- #11: e-drive amplitude (e-drivemode 1 and 4 only)
- #12: e-drive jitter (default 10, e-drive mode 4 only)
- #13: e-drive mode:
- 0: disable e-drive (default)
- 1: frequency drive active
- 2: feedback mode active
- 3: external drive mode active
- 4: frequency drive with jitter active
- #14: default damper time (used when note-off + release is not used but only
note-on with velo=0). On cold boot or reset, this value is set to 40. The
range is 6ms to 747ms.
- #15: all dampers on/off. With value 0, all dampers
are released. With value 127, the dampers stay on until released by sending
value 0. Reception of new
note-on commands will release the dampers for those notes. This controller
is non-sticky, so it can be sent many times with the same value.
- #16: if set to 0, note-on commands will always release
the damper, regardless the value set for it with the release byte or by controller
#14. If set to any other value, it is possible to attack the rods with the
damper still on. By default this controller is off.
- #64: Sustain on/off
- 0 or any value < 64 enables the dampers. Damping force is controller
either by the release byte of the note-off command, or by the value set
with controller #14
- 64:or any value > 63 disables the dampers, so sustain is active.
Sending this command immediately releases all dampers.
- #66: Power on/off: This resets the controllers to the default cold boot
- #123: All notes off. Releases all dampers and switches off the lights. It
does not reset any controllers.
Pitch bend: used for setting a frequency for the e-drive mechanism (14 bit
resolution, range 0-4096 Hz). This will only work if controller #13 is set to
Program change: used to steer the operational mode of the robot.
- Value 0: robot fully under external midi control
- Value 1: Interactive robotic mode active
<Rodo> uses midi channel 7 (counting 0-15)
- sizes: 1200 mm x 1040 mm x 900 mm
- weight: 65 kg
- power: 235 V / 220 VA
- tuning: A=440 Hz
- Loudness level: 20dBA to 86dBA
- Insurance value: 12.500 Euro
Design and construction: dr.Godfried-Willem
Collaborators on the construction of this robot:
- Mattias Parent, Moniek Darge, Laura Maes (requisites and mechanical help)
- Sebastian Bradt. Xavier Verhelst (application research)
- Johannes Taelman & Kristof Lauwers (ARM board firmware for the e-drive
Music composed for <Rodo>:
- Godfried-Willem Raes: Namuda Study #44, "Rods for Rodo" (2014)
- Sebastian Bradt "in the works" (2014)
- Lara Van Wynsberghe: 'Kutstuk' (with <Aeio>) (2016)
- 05.09.2008: Kuhnke solenoids ordered, anticipating the construction of a
completely new toy piano.
- 12.07.2012: Cast iron bar (40 x 40 x 1020) ordered from Demar-Lux to serve
as a holder for the tines.
- 12.07.2013: First practical sketches and drawings. Tone rod construction
principle and soundboard.
- 19.12.2013: Experiments with Maxon motors on tone rods and strings.
20.12.2013: Tone rod bronze delivered from Demar Lux. These rods are 8 mm
diameter and the alloy is Cu Al10 Ni5 Fe4 (Aluminium-bronze). Weight per meter
of length: 0.4 kg. Calculated density: 7.957 kg/l. (after the data sheet:
7.6 kg/l). Brinell hardness: 180. Tensile strength:640 N/mm2. 0.2% stretch
limit 270 N/mm2, stretch: 10%. This alloy contains 8.5 to 11% aluminum, 4
to 6% Nickel,, 2 to 5% Iron, and less than 1.5% Manganese, the remainder being
- 21.12.2013: Comparative tests on different materials and alloys. The bronze
rods were selected as the most 'musical' ones.
- 22.12.2013: Construction of the cast iron bar to hold the tone rods. This
bar is 1020 mm long, square section 40mm x 40mm. Weight: 12 kg. Alloy: GG25
(DIN 1691). There will be place for 31 rods if we stick to a distance between
rods of 30 mm. This is the construction drawing:
Here are some pictures taken during this construction session:
- 23.12.2013: Three test rods mounted and checked for produced pitch.
In the next picture the set screws for tuning adjustment are shown:Calculation
utility, based an acoustics theory books formulas programmed in Power Basic
Console Compiler. (Source code: rodo.bas). Kuhnke solenoids selected: type
HM157.F.24 VDC.100%ED. Extra bronze rods ordered from Demar-Lux. Hand reamer
8.0 mm purchased as well as a new set of M6 threading tools (hand taps).
- 24.12.2013: Calculation and design works. M6 x 16 set screws bought from
MEA. Work slowed down due to an emergency admission in the hospital: muscle
fraction or hernia attack.
- 25.12.2013: Precision measurement of resonance under forced excitation.
- 26.12.2013: Working out experimental results and comparison with theoretical
values. A program written to calculate all rod lengths such that we can start
sawing all rods to size.
- 27.12.2013: Total cost of the bronze tone rods will amount to 523 Euro.
The cost of this alloy amounts to 27.52 Euro a kg. Further drilling of the
5mm holes for clamping the rods. Threading to M6 for set screws. Surface grinding
to remove rusts and light polishing. All holes for the rods drilled to 7.9
mm and further honed to exactly 8.00 mm. First set of six tone rods cut to
size and tested for tuning.
- 28.12.2013: The total length of all rods together will be 21.597 m, so with
a mass of 0.4 kg/m the weight of all staves together will be 8,638 kg. Experiments
with different soundboard shapes and materials. Polystyrene works well if
clamped between the rod-holder and a strong piece of staff material. Wood
also sounds well, but we may have trouble finding a large enough soundboard.
Two end holes drilled
in the cast iron stave and provided with M12 threads for mounting the soundboard.
Start construction of the solenoid holding profile. This will be made from
a length of aluminum 50x30x3 L-profile. We did choose aluminum because its
better for dissipating the heath from the solenoids. The solenoids are mounted
with two M3x6 bolts each.
For the beaters
we plan to use M4 threaded Bakelite spheres. Inserts to fit the M2 threads
on the solenoid anchors to be constructed from M4x8 setscrews.
- 29.12.2013: Damn, Sunday... shops are closed. Continuing work on the solenoid
assembly. First attempt to prepare a beater: the 15 mm Bakelite balls have
an internal M4 thread, about 12 mm deep. So, we drill a 1.4 mm hole in a M4x10
setscrew on the lathe and after this we cut an M2 thread -by hand, in three
passes- in the hole. We will have to do this 31 times... First attempts very
- 30.12.2013: Considering the possibility to add a very strong electromagnet
just under the cast iron bar to allow the rods so sing. The input signal could
either come from the rods (in controlled feedback mode) or from an ARM processor
with properly adapted wave synthesis. Design of a damper bar to be placed
over the rods, driven by another set of solenoids. To 50 mm wide pieces cut
of from an HEA 100 profile to test usability as standoff's for the cast iron
bar. M4 x 8 setscrews bought from MEA, together with a new set of handtaps
M2. Threading these setscrews with M2 threads seems to become an endless,
if not impossible undertaking by hand. In a couple of hours, all our M2 taps
broke and we didn't even get a single bolt finished... At a cost of 30 Euro's
for a set of taps, this is becoming prohibitive. Looking for alternatives:
having this part of the job done in an automated factory, or drill 2 mm holes
and glue the anchors to the set screws with cyanoacrylate glue.
- 31.12.2013: Flatface grinder (Bernardo, Austria), ordered months ago, came
flowing in. Design of a possible driver circuit for the electromagnetic activation
of the cast iron bar. We will have to take the octaving problem into account!
We could use an Axo ARM board to do the signal processing, if Johannes Taelmans
firmware is capable enough for handling this. Version 1 of a welding plan
for the chassis and trolley worked out.
- 01.01.2014: Wheel base worked out. We will use spoke wheels again, as on
- 02.01.2014: Thread adapters M4-male to M2-female seem to exist! We ordered
them from Newport, type nr. TR-M2M4. They are expensive though: 360 Euro for
Spoke wheels ordered from Kaiser+Kraft. (415 mm x 60 mm, 120 Euro each).
- 05.01.2014: What about using an old bulk eraser as an electromagnetic driver
for the cast iron bar? Digged one up dating from the seventies: Radio Shack,
100 W / 220 V bulk eraser, maximum on-time: 1 minute. Tried on Rodo and it
seems like it's going to work if we feed if with a high voltage signal. The
DC resistance of the coil was measured as 21.27 Ohm, the inductance as 312
mH at 1 kHz, raising to 325 mH at 100 Hz and 344 mH at 10 kHz.
The picture shows the electromagnet as found in the bulk eraser.
- 06.01.2014: Design of the power amplifier module for driving the electromagnetic
exciter. The M4x6 setscrew, M2 taps and the vibration dampers ordered from
Fabory came in.
- 07.01.2014: Steel cutting and welding works on the under-chassis. Horizontal
structure uses stainless steel 50x50x2 profiles. Wheel holders: 50x30x3. Welding
plan further worked out.
The pictures show
the assembly of the holders for the cast iron bar. The soundboard is not mounted
here, but will be fitted between the HEA100 profile and the rubber damper.
- 08.01.2014: Experiments with soundboard materials. Start construction of
the damper assembly, using Lucas Ledex tubular solenoids (push type), from
a length of aluminum 50 x 30 x 3 L profile (same as used for the beater assembly).
The holes for the solenoids are 14 mm and the threads on the solenoids are
M14 x 1.5. The distance between the holes is -as for the beaters- 30 mm. We
will have to provide a spring inside the solenoids with a strength such that
as rest the dampers to not make contact with the tone rods. We may have to
order these custom made from Veren Algoet. Here is the damper solenoid assembly
without the plungers and the damper heads:
- 09.01.2014: Design of adjustable mounts for both the beater- and the damper
assembly. Adjustment should be possible both horizontally and vertically.
Horizontal range: 80 mm, vertical range 120 mm. Cutting of the 31 damper felts
(diameter 25 mm, 10 mm thick) using the arbor press and a dinking die.
These felt pads will be glued on 25 mm conical valves mounted upside down.
The centered 2 mm hole has to be slightly enlarged as the plungers have a
stem diameter of 2.35 mm.
- 10.01.2014: We cannot assemble and test the dampers as long as we did not
fit the return springs. The felt dampers have to be glued on the plungers
and then cannot be easily removed again. The ordered M4-M2 thread adapters
came in from Micro-Controle Spectra-Physics s.a.
- 11.01.2014: Start coding for the beater PIC-controller boards. The source
code for these, under development, is at http://www.logosfoundation.org/instrum_gwr/rodo/picworks/Rodo_Beaters1.bas.
It must be compiled using the Proton Compiler in combination with MPLAB.
- 12.01.2014: First version of the firmware for the damper controller boards.
This can be found back at http://www.logosfoundation.org/instrum_gwr/rodo/picworks/Rodo_Dampers1.bas.
We still have to assemble the boards though. Support for <Rodo> added
in our GMT software, so we can perform the required testing. Construction
of the return springs and the brass discs to retain them on the plungers holding
the dampers. To make these brass discs, we used the arbor press with a 10
mm dinking die on 0.5 mm thick brass foil (sheet metal).
The brass discs were glued on the flat plunger end using Loctite 401 cyanoacrylate
glue. For the return springs we used the same type as we had custom made for
the player piano robots. Note that very much on purpose we dropped the springs
over the plungers whilst the glue had not fully set, thus they are also glued
to the plungers at their end. Since
the springs unavoidably tend to make the plungers, and thus with them the
dampers, bounce on release, we may have to add a felt covered debouncing bar
over the entire assembly. This is as yet to be experimentally found out. Gluing
of the 25 mm felt discs to the inverted conical valves, using Loctite 5920
copper silicon. We prepared the 2 mm holes in the conical valves by hammering
a spare plunger with the 2.35 mm shaft in them to a depth of 6 mm. This enlarges
the holes in the wood slightly and makes a tight fit later on. As the silicone
tends to creep slightly through the hole, we may have to use the arbor press
again to force the plungers into the felt holders.
- 13.01.2014: Suitable transformer digged up for the damper power supply:
12V /25A. Firmware version 1.0 for beater-pic and damper-pic uploaded in two
chips and tested on our test-board with the GMT code. Functionally everything
seems to run fine. Controllers 14,15,16,64 tested under GMT. Note-off with
release runs fine as well. The scaling of course will depend on the behaviour
on the instrument itself. Firmware source code edited in order to program
the second beater and damper PIC's. In principle we have all four chips ready
for testing now. Soldering works on the midi-pulse boards started.
- 14.01.2014: Design work for the power supplies. As we want to avoid using
SMPS types (because of the trouble we had with them in the past with fast
switching solenoid loads and both EMC and emitted ultrasound) , we have to
come up with a very stable design capable of delivering at least 20 A. A bunch
of LT1084CP12 type 12 V/5 A regulators, operating in parallel may be a viable
solution. If we add power diodes and maybe a small resistor in series with
the output, we could even easily get at ca. 10 V, just a bit over the 9.4
V 100% duty cycle specification for the damper solenoids.
- 15.01.2014: Traced a factory that could cut out the required sound board
from polystyrene (Isomo, brand name for styrofoam).
- 16.01.2014: Technical drawing prepared. The voltage regulators 12 V/ 5 A
(LT1084CP12) came in from Farnell together with a fresh load of 18F4620 microprocessors.
Further design and calculations on the power supplies.
- 17.01.2014: Drawing a design for a PC board. If we want to place all (heavy
and large) components on the board, we need at least a 3 mm thick PC board.
Taking into account the very high currents involved, we decided to hand-make
a double sided PC board using adhesive copper foil. It looks a bit primitive...
- 18.01.2014: Assembly of the experimental board for the 25`A / 12 V power
supply. Carefull tinning of the adhesive copper foil is essential as the adhesive
itself in non-conductive. This is the copper side after tinning: We
got the entire power supply ready now. Testing also performed. Voltage over
the big capacitor measures 15 V. 12 V light supply measures 12.0 V, whereas
the outputs for the damper solenoids measure 11.8 V without load. Here is
the finished module:
Sizes are 270 x 260 x 170 mm, or about twice as large as a comparable SMPS
power supply. The output terminals are formed from brass M4 bolts and nuts,
soldered on the copper side of the board.
- 19.01.2014: Soldering works on the solenoid driver boards. 112 IRL640 Mosfets
in total on these boards alone... Some
3500 solder joints to be done. Start work on the assembly of the 48/60V power
supply. Here also we use an epoxy carrier board.
- 20.01.2014: Further work on the 48/60V power supply. This carrier board
can also hold the transformer for the 5V logic power supply. The regulators
are on board of the pulse boards, so these just need a 6 V AC source. Sizes
are: 270 x 120 x 140 mm. Start
construction of the carrier board for the ILP HY2005 power amp module and
its toroidal transformer. The link has to be soldered on the module, as required
for 8 Ohm operation. For good impedance matching, we will have to use a matching
transformer on the output. Maybe be could recycle an old vacuum-tube amplifier
output transformer. We should still have a few 100 W vacuum tube amplifiers
around... Maximum output voltage from the ILP amp is 31 Vrms, so a 1:10 voltage
ratio transformer should do the job.
- 21.01.2014: Finishing the power amplifier module. This sizes 270 x 120 x
90 mm. It's not large
enough to also fit the required impedance matching transformer. For this we
could also try a toroidal 2 x 35V to 230V rated for 160 W. It might be a good
idea to fit the bulk eraser coil with a temperature sensor that could be read
by the ARM board processor, such that a burn-out protection would be implemented.
- 22.01.2014: Instead of providing a temperature sensor on the bulk eraser,
we decided to simply equip it with a temperature switch on the windings, such
that the circuit breaks if ever the coil gets too hot. Looking at the design
now, it seems a bit stupid to use the impedance transformer. Instead we would
have done much better by rewinding the coil on the coil former of the bulk
eraser assembly to give it an inherent 8 Ohm impedance... But, obviously,
coil winding by hand is always a pretty tedious job. Block terminal contacts
ordered from Farnell. Styrofoam boards (4 pieces, as we expect accidents to
happen...) ordered to use as soundboard. Redesign of the stainless steel structure.
Suffering from a hernia, we have to postpone the cutting and welding works
a bit it seems.
- 23.01.2014: Very gentle -because of the hernia- TIG welding works on the
wheel base for the back wheels. Stainless steel profiles used: 50 x 30 x 2.
Start working on
the adjustable holders for the beater and damper mechanisms. The are to be
made from 10 mm thick staff material.
- 24.01.2014: Holders with slides for M8 and M10 bolts finished. Cutting,
welding, grinding. One for the left side, one for the right side. The vertical
slide made from 25 x 10 staff material, the horizontal one from 20 x 10 material
such that the total height is exactly 50 mm.
- 25.01.2014: Holes drilled in chassis and slides mounted and tested. Construction
of the slide for mounting the electromagnetic driver. Three bars of 20 x 10
x 300 stainless steel, welded together with two 10 mm gaps. The core of the
driver is only 24 mm wide, so we need a pair of spacers to adjust it such
as to strike in the middle of the 40 mm wide cast iron bar. The spacer ought
to be 8 mm and can be welded on the slide. Mounting
holes for the solenoid are 5 mm. Bolts for the slide must be M10 x 70 or M10
x 80. Possible front wheel mechanism found in the hardware store. Hoping to
dig up a suitable wheel now from our collection...
- 26.01.2014: Finalizing the e-drive mechanism. Start construction of the
bend sides of the main chassis. These sides are made from two pieces of 50
x 5 x 820 stainless steel. Bending by hand in a large vise clamp. Welded on
the back chassis on the welding table..
Further works on the front wheel design. Building height of the wheel will
be 240 mm. The mounting plate measures 110 x 140 mm.
- 27.01.2014: Still waiting for the spoke wheels, the brass rods and the styrofoam
soundboard... Panel voltmeter (moving coil) with range 300V ac added for monitoring
the e-drive output. (Type YH670, class 2.5) Mounted on an small aluminum subpanel
on the board housing the impedance transformer. Holes drilled for he circuitry
holding panels to be cut out from 2 mm thick stainless steel plates. So, we
decided not to weld these on, but rather to make them removable for ease of
maintenance and final assembly. Instrument under construction explained to
a small group of students.
- 28.01.2014: Cutting and bending of the mounting plate for the power supplies,
mains switch, I/O connectors etc. Cut from 2 mm thick stainless steel, left
over from the construction of the Logos building. The wheels came in, unfortunately
they came with spindle holes 20 mm in size instead of the 12 mm we had already
drilled in the chassis... Holes drilled for mounting of the supply components,
for the MIDI I/O connectors, the mains entry, mains power switch and a switch
for mode of operation selection (autonomous robot / midi controlled automaton).
- 29.01.2014: Mounting of the connectors on the bottom plate. Test mount of
the bottom plate assembly. We need 6 mm hole mounting studs in PTFE or Epramid.
The styrofoam sound boards still did not come in!
- 30.01.2014: Bending of the back wheel structure to bring it perfectly in
shape after welding deformations. Construction of the 20 mm shafts for the
- 03.02.2014: The stock of bronze rods came in from Demar-Lux. Still no styrofoam
- 05.02.2014: M12 threads made in the wheel shafts. The wheels can be mounted
now. Cutting of the tone rods from bronze staff material... trouble though:
the composition is different than that of our test staves. Either we have
to re-order the staves, or recalculate the staves for the new alloy.
- 06-17.02.2014: Research on sensor systems and information retrieval to be
used for the robotic components in <Rodo> but also for the gesture recognition
coding under GMT.
- 18.02.2014: Test mounting of the power supply carrying plate on the lower
wheel chassis. The M10 mounting bolts will have to welded op the base plate.
Test mount of the power supply assemblies on M6 MF threaded vibration dampers.
Cutting of the two holders for the 12V LED spotlights underneath (50mm diameter
stainless steel tube, length 50mm).
- 21.02.2014: Distance holders turned on the lathe from epramid staff material.
Vibration dampers would after all have been overkill here. M10 bolts welded
on the power supply assembly.
- 22.02.2014: Spotlight holders constructed for mounting on the power supply
plate. These are adjustable.
- 23.02.2014: Assembly of the back wheels, the wheelbase and mounting on the
horizontal skeleton. Welding on the horizontal structure.
construction of the front wheel structure. Still very handicapped by a hernia...
- 24.02.2014: Construction of the front wheel. Welding works. Wheel mounting
plate: 160 x 100 x 10, with four 10mm holes. Vertically inclined pole: 100
x 50 x 2 profile. Mounting plate welded on chassis, cut out from 3mm stainless
- 25.02.2014: Drawing and plasma cutting of the carrier plate for the microcontrollers
and the robotic components. Construction of two light holders for the front
next to the frontal wheel. First tests with styrofoam soundboard.
- 26.02.2014: Drilling and honing of all mounting holes on the microcontroller
plate. The plate can be taken out by loosening the five M10x50 and two M10
x 25 bolts. Construction of the mounting plate (vertical) for the four PIC
processor boards. This assembly mounts on the backside of the horizontal plate
with two M12 bolts.
With the help of Sebastian, Mattias and Kristof, we managed to flip the entire
construction and bring it back in position on the welding table...
Two blue LED spotlites
mounted in their holders on the front and two yellow LED spotlites in the
holders on the power supply plate.
- 27.02.2014: Instruction to the instrument building students at the conservatory
about the ongoing <Rodo> project. Tools and techniques explained. Wiring
of the on/off switch and the midi-input connections. We will leave the drilling
of the mounting holes for the robotic components for later on, as we do not
now the sizing of these components yet.
- 28.02.2014: Start wiring of the power supply lines.
- 01.03.2014: Continued wiring of the PIC processor boards. Mounting and wiring
done (except the dampers and the solenoids) such that we can test the board
and the initial coding in the firmware. Yellow LED spotlites mapped on notes
114 and 115 and controlled by the Dampers-1 microcontroller board. At first
boot, with all voltages applied, everything seems to run fine.
- 03.03.2014: Tracing a suitable transformer for the required +24V voltages
for the LED strips and the sonar sensor. An old transformer block from a HP
inkjet printer may do the job. Rodo project demonstration for Brent Wetters.
- 04.03.2014: Design of the dual +24V power supply.
- 05.03.2014: Dual + 24V power supply soldered and tested. HP transformerblock
mounted on the power supply chassis plate. This was done using two strap ties
and some parabond under the transformer housing. Wiring of the e-drive module.
We mount the components for the 24V supply on this same subchassis module.
The 24V power supply has two separate outputs and uses a Weidmueller connector.
- 06.03.2014: All ground connections made. Alu-bronze bars delivered. Bronze
cutting with the students.
- 07.03.2014: Front lights wired. Test mount of the mechanism. Cutting and
first tuning of the bronze staves.
Two out of the eight rods in the new delivery appeared to be cast from a different
alloy again, so we had to re-cut them. A lesson learned: never trust batches
of delivered alloys to be identical...
- 08.03.2014: Support for the front of the styrofoam soundboard designed and
beaters loosely screwed on the beater anchors. The wite stuff underneath the
beaters on the picture is the styrofoam soundboard.
Start wiring of the solenoids. Wiring just the beater solenoids took us a
full day and still we have to do the Weidmueller connectors. Wire colors follow
resistor color coding, staring with note 48 being black. The common positive
voltage is the thick red wire. A white LED strip (24V) is mounted on the userside
of the beater assembly. These LED strips require 240mA current (4.5W), so
we should be carefull not to exceed the limits of the 24V power supply if
we are adding more of these lights...
- 09.03.2014: Wiring of the beater Weidmueller connectors: two boards. If
we mounted the tone rods, rodo could play already... Electrical tests o.k.
Design of a strong red LED light assembly for the underside. This uses 1W
LED's in SMD technology. Styrofoam soundboard cut to shape with a razor blade.
Frontal holder for the soundboard welded on.
- 10.03.2014: First test mount of the rod assembly on the styrofoam soundboard:
deceptive results, as the styrofoam is clearly not strong enough to hold the
weight and the pressure of the rod assembly. We could try to increase the
contact surface, for instance by mounting the rod assembly via a piece of
wood on the soundboard. On the underside, a larger surface is required as
well. So, we did cut out four pieces of wood and indeed, now it works fine
and with good resonance. In the definitive version we should remake these
pieces of wood from real good quality hardwood 10 mm thick and 50 mm wide.
(Meranti) As an alternative we could also try out titanium here.
- 11.03.2014: In need of long bolts M12, M10 and M8... up to MEA. Four support
plates sawn out from long aged tropical hardwood, thickness 8 mm. Now the
sound is o.k. It may be better not to support the front of the styrofoam,
as supporting it gives some damping of the lower frequencies.
First tests of the electromagnetic drive mechanism, using a tone generator
leading to a large smoke stack... Something is fundamentally wrong here...
Almost certainly we exceeded the 500mV max. input level.... Analysis of the
board revealed that the elco's exploded. 4.7mF/63V types, presumably with
an MTBF below 3000 hours. We will try to replace them with decent quality
100V types and hope the amp has survived it.
- 12.03.2014: Apparently, not the elco's exploded, but the HY2005 module itself.
Bad luck... and high costs. As the HY2005 is no longer in production at ILP,
we will have to replace it with the ILP HY2004 type and adding a power supply
externally. Mattias Parent helps us out adjusting the Bakelite beaters for
a trajectory of 5.5mm to the tines. <Rodo> produces its very first tones
and scales under computer control! Apparently we forgot to implement the blue
LED spotlights on the front in de firmware for damper PIC1. Firmware revised,
not yet in the chip. GMT test-code adapted to make measurement of good velocity
scalings for the beaters possible. Our tests in this matter lead us to new
analysis of solenoid behaviour under fast repetition conditions. If the time
between two pulses becomes smaller than the fallback time of the anchor and
its load, the anchor will assume a 'floating' position without coming down.
As the pulse time is increased, the distance to the struck object becomes
smaller, repetition time can be increased but sound volume will go down. If
you go beyond the duty cycle limits, obviously the solenoid will burn out.
This confirms our observation that for very fast repetition rates, very low
velocity values have to be used.
- 13.03.2014: Working session with the instrument building students at the
Conservatory. Acoustic theory of styrofoam explained and demonstrated. Introduction
in welding technology. Firmware version 1.2 uploaded for beater PIC2, with
'dead-time' after strike provisions and new velocity scalings.
- 14.03.2014: Continued work on the damper assembly. All solenoids wired:
a full working day.... Weidmueller connectors to be done.
- 15.03.2014: Mounting of the damper felts on the solenoid anchors. Wiring
of the Weidmueller connectors. The boards are up and running now. Further
work on the firmware is required.
- 16.03.2014: Bounce-back bar over the damper assembly mounted. This
bar carries also the engraved brass nameplate 'me fecit logos'. Firmware development
for the damper controllers. Midi implementation updated. The time the dampers
stay in contact with the tines can be controlled within the range 6 ms to
767 ms. Either the note-off release value or controller #14 can be used to
control this. Lights 116,117,118,119 implemented on the second damperboard,
although we have as yet no lights connected there. Rodo plays well now and
can be given in the hands of users/composers for evaluation. All controllers
implemented sofar tested with the coding in GMT.
The left blue light appeared to be broken. Probably because of the strong
electromagnetic fields welding works caued too close to the LED... LED spotlite
- 17.03.2014: Meeting with Kristof Lauwers on the way we are going to implement
the electromagnetic drive mechanism. The power amp (HY2004) has been replaced
and works fine now. We have to keep an eye on input and output conditions
though. Never ever exceed 500mV on the input! The frequency range should be
limited to 20Hz - 260Hz range. In the lowest range, resonances with the dampers
- 18.03-21.03.2014: Kristof Lauwers at work on the development of the code
and patches for the ARM board, Axo project.
- 21.03.2014: Two red LED lights mounted on the underside. These need a 18
Ohm series resistor to work on 12 V DC. Each of these LED clusters draws ca.
200mA. Here is the datasheet.
- 22.03.2014: Finalisation of the wiring for the red lights. These are mapped
on midi notes 120 and 121, controlled by the PIC for the second set of beaters.
Power comes from the +12V lights power supply.
- 23.03.2014: Continued tests and evaluations on the e-drive mechanism. GMT
test-code further improved.
- 25.03.2014: Work session with the Axo firmware as developed by Kristof Lauwers.
- 26.03.2014: Axo board problems: input attenuator unavailable, variable midi
channel not implemented, strange behavior with output volumes. To be discussed
with Johannes Taelman. It seems the audio inputs on the board are very high
sensitivity and do not have an attenuator...
- 27.03.2014: Wiring of the Honeywell 944-T4V-2D-1C1-130E distance sensor
connector. The connector is Hirschmann type ELKA 5012 PG7, 5 pole , order
nr.933 170-100. The responsiveness of the distance sensor appears to be very
slow. Here is a link to the sensors manual.
- 28.03.2014: Distance data is refreshed only once every 1.2 seconds using
this Honeywell sensor.
- 31.03 - 03.04. 2014: Continued work on the ARM firmware by Kristof Lauwers.
- 03.04.2014: <Rodo> lifted from the welding table as we needed it to
be free for the construction of the <Snar2> robot. Now set up in the
center of the tetrahedron...
- 06.04.2014: The first interactive piece for <Rodo> is in the making:
Namuda Study #44.
First rehearsal with Dominica Eyckmans.
- 07.04.2014: Further debugging of the ARM coding.
- 08.04.2014: There must be a small bug in the PIC firmware for the beaters.
It doesn't seem to work under running status conditions. The dampers behave
- 09.04.2014: Bug found in the beater firmware. Repaired and both chips reprogrammed
with version 1.3
- 10.04.2014: Adding rotating red warning light, 24V. Mapped on midi note
126 and controlled by beater PIC 1.
- 11.04.2014: Television shooting session with Rodo for VRT 1.
- 12.04.2014: Attempts to power the ARM board from the general +5V V DC supply
such that is does no longer require the USB connection. Code tested for playing
Rodo with the dampers alone.
- 13.04.2014: Rehearsal session with Dominica Eyckmans:
Rods for Rodo, namuda study #44.
- 14.04.2014: Stand-alone operation of the ARM/Axo board succesfull. The connectors
to the board are a bit shaky however. Start design of a PC board for the analog
input channels and sensing components.
- 16.04.2014: <Rodo> plays for the first time in public.
- 16.07.2014: Impedance transformer board soldered and mounted for the piezo-disks.
1:10 audio transformers used. This way there is no more risk for overloading
the ARM-AXO board input.
- 11.02.2016: Failure of the e-bow mechanism. Apparently the power amp is
dead. Maybe we should redesign this, for instance by using a Visaton exciter
instead of the electromagnet. This would greatly simplify the circuitry. However
we first have to find out what it sounds like. Drivers already ordered from
- 14.02.2016: Repairing the original circuit, with an added diode compressor:
HY2004 amplifier module replaced. Measurements: with 160V ac on the output
transformer and over the driven electromagnet, the HY2004 gets pretty hot.
The amp output is delivering 23.5V to the transformer then, so it ought to
be well within specs... (66V pp output, that is).
- 16.02.2016: HY2004 burned out again, despite the input protection, in the
music for our 'Oorsprong' production... Alternative approach seems required.
- 18.02.2016: 'Oorsprong' production done by using an external Maranz amplifier
replacing the HY2004. This is a temporary fix though.
- - calculation of a parameterized model for the tines
- - construction of alternative rod sets in beryllium copper and phosphor
- - testing and finishing electronics boards for interactivity.
- - wiring of the the robotic components
- - welding works on the frontal section (distance sensor assembly)
- - design of the interactive robotic components: radar interfaces for gesture
- - ARM board firmware for the sensor components (Axo platform) by Kristof
Lauwers and Johannes Taelman.
Last update: 2016-08-20
by Godfried-Willem Raes
Further reading on this topic:
MECHEL, F.P., "Formulas of Acoustics"
OLSON, Harry F. "Music, Physics and engineering"
- ed. Dover, New York (1952), 1967
RAYLEIGH, John William Strutt "The Theory of Sound" (2 vols)
- ed.: Dover Publications Inc., NY, 1945, ISBN 486-60292-3
- een reprint in twee boekdelen van de originele uitgave
uit 1894. (ed.MacMillan Company)
TALUKDAR, S, "Vibration of Continuous Systems",
- ed.:Dept.of Civil Engineering, Indian Institute of Technology Gowahati -
Technical data sheet, design calculations and maintenance instructions:
Technical data and design elements. Maintenance instructions and replacement
Technische gegevens, ontwerpberekeningen en instrukties voor onderhoud en demontage:
- Beaters: Kuhnke Gmbh, type HM157.F.24VDC.100%ED (website: www.kuhnke.de,
e-mail: email@example.com). A
copy of their catalogue for linear solenoids containing the data sheets is
- Dampers: Lucas Ledex, (Saia Burgess) type 195225-229, STA, 9.4V dc @ 100%
- 7Watt, nominal traject 5.1 mm, maximum traject 17.8 mm. Length:39 mm, Plunger:
15.3 g. Total weigth: 87.3 g. DC-resistance: 12.8 Ohm. Maximum power @ 10%
duty cucle: 70 Watt, 11.9 N. Mounting thread: M14 x 1.5.. Lifetime: 25 miljoen
cycli. (= 86 dagen ononderbroken roffelen aan 8 cycli per sekonde).
- Electromagnetic driver: Bulk eraser coil (Radio Shack, 100 VA, 220 V). Inductance:
320 mH, DC resistance: 21.27 Ohms.
Tone rods: Material: Aluminum-bronze, Cu Al10 Ni5 Fe4, diameter 8 mm. Ordered
from Demar-Lux bvba.
Cast iron bar: 40 x 40 x 1020, GG25. Ordered from Demar-Lux bvba. http://www.demar-lux.be
- Circuit drawing - pulse boards / damper boards: (download to view at 100%
- Source code for the firmware for the beaters notes 48 to 63: http://www.logosfoundation.org/instrum_gwr/rodo/picworks/Rodo_Beaters1.bas.
- Source code for the firmware for the beaters notes 64 to 78:
- Source code for the firmware for the dampers notes 48 to 63:
- Source code for the firmware for the dampers notes 64 to 78:
- Hex dumps and assembly code is available as well.
- MidiHub board: (download to view at 100% size)
- Power supplies:
- +48 V/ 60 V - 150 VA supply (for the beaters)
- +12 V / 25 A supply for the dampers and the lights (300 VA)
- +/- 55V supply for the power amplifier (250 VA)
- + 24V / 500mA (two separate outputs) for the sensor components and the
- +5 V supply for the microprocessors (30 VA)
- Circuit overview:
- E-drive circuitry (2014):
Changed 14.02.2016 like this:
- Data sheet for the ILP HY2005 amplifier
Toroidal transformer: Noratel TA250/40. Farnell order nr. 953 0835
- Toroidal transformer: Block RK160/35 (www.block-trafo.de)
Wheels: Ordered from Kaiser + Kraft, Tente, art.nr.95, 415 mm x 60 mm,
polyurethane. (back wheels, with spokes)
- Front wheel: diameter 200 mm, building heigth 240 mm.
- ARM processor board: AXO board designed by Johannes Taelman. Version Axo
V0.3, 2013.12.10, component mount 90140313.
- Distance sensor: Honeywell, 944-T4V-2D-1C1-130E. Measurement range: 350mm
to 3500mm. Power supply 24V. Beam angle 8 degrees. Working frequency: 130kHz.
Data sheet and programming manual.
- Two LED spotlights on the bottom plate (Yellow, 38 LED's, GU5.3, 1.7W,
BaseTech nr. 574584) (12V)
- Two blue 1W single LED spotlights underneath the frontal part. (12V)
- One white LED light strip (24V, 4.5W) on the backside.
- One white LED light strip (24V/4.5W) on the beater assembly
- Two Red LED spotlight underneath: Kingbright
led clusters. (12V, 2.4W)
- One Red rotating flashlight (24V)
|Druksterkte bij 10% vervorming (korte duur) se=10% of CS (10)
|Lange-duur druksterkte se=2% of CS (2)
|Buigsterkte sb of BS
|WarmtegeleidingscoŽfficiŽnt lD = lR W/m.K
|Vochtopname bij onderdompeling % v/v
|Lineaire uitzettingscoŽfficiŽnt a m/m
|Warmtecapaciteit C J/kg K
|Temperatuurbestendigheid (min/max) T
||-180 + 80
||-180 + 80
Robody Pictures with <Rodo>