[Nederlandstalige versie]

Robot: <So>

This musical robot consists of an old sousaphone with an automated playing head and automated valves. Wind supply is also automated. Controlling this robots is realized with a nonstandard midi protocol. (cf.. 2072.html in our course on electronics for the performing arts). The sound generating mechanism mimics human lips and does make use of the normal mouthpiece of the instrument. A moving coil valve activates a leather pad (actually one taken from the lowest keyholes of a tenor saxophone) that opens and closes the air traject through the mouthpiece. We did spend a lot of research time in finding a mechanism producing a realistic sound. Hundredths of attempts using solenoid valves failed, because the magnetization of the iron alloys used is way too slow to open and close any kind of valves at speeds exceeding 40 Hz. Hence we decided to use a moving coil mechanism in a permanent magnet, much like the action of a regular loudspeaker. This mechanism is controlled by a switching signal of a frequency corresponding to the note to be played. At the same time the valves (activated by solenoids) are pushed such that resonance through the instrument does occur. Pressure , derived from a smal axial compressor, is applied to the artificial mouth assembly.

Dynamic control is not an easy matter, and requires two interdependent parameters: wind pressure and signal amplitude. The valve membrane amplitude diminishes and the center point of movement symmetry shifts with frequency, when pulsed DC is used. Thus to compensate for the lower valve excursions at higher frequencies, the wind pressure has to be increased. On theoretical grounds it would have been better to adjust the distance between valve seating and mouthpiece in function of amplitude and frequency, but this posed us way too many mechanical problems. Thinking along this path, we finaly went for a DC pulse steering for the lower notes and transformer coupled AC steering for the higher notes in the compass.

The overview of the circuit boards used to construct this robot look like:

The first building block parses and converts the incoming midi data to parallel bytes. Click here for circuit details. It is build around a 6402 UART chip and performs very fast due to the lack of a microprocessor. The input wiring can be easily converted to accept DMX signals, making very long wires possible. With midi the practical limit seems to be 15 meters. The DEMUX board converts the received data to an 8-bit data bus and an adres bus. Click here for circuit details. This board also houses a BS2 pic controller used to steer the radial compressor. The variable frequency output signal from this processor is transformed to a regular 230V level using a transformer as shown in the overview. For the sound generating mechanism we used a note synthesizer build around an old S50240 chip. Click here for circuit details. The frequency outputs of this board are AND-ed with the note select signals on the speaker driver board. Click here for circuit details. The solenoid valves are controlled by the logic on the same board. The power DAC is very primitive, and makes use of relais switched power resistors.

Note on the push tubular solenoids used to activate the pistons:

Brand: Lukas Ledex Dormeyer, 195207-228, 1" x 2", with 60 degrees plunger . Coil winding resistance: 19,2 Ohm. The following specs are valid at 20 degrees celcius. Maximum holding force is 29N

These solenoids do not deliver enough starting force to start the valve movement. Therefore we switch them in series with a 14.3 Ohm resistor (10 Watt) and have a 2200microfarad electrolytic over them. When we feed the solenoids from a 24V supply, the solenoids when firing will see a voltage of 24V across them for a time RC= 42ms, enough to start the movement with a force of about 5 Newton. When energized, the voltage drops to 14V, enough to hold the valves pressed down:

This way there should not be a risk of burning out the solenoids. The picture below shows how it looks like during construction.

Power DAC for amplitude control of moving coil driver:

The resistors are rated between 5 and 25 Watt. Maximum power that can be applied to the driver (Sonics SLE60) is limited to 60Watt. Originally we used series connected power mosfets to form a high power AND function, but since the gates of the upper mosfets are exposed to up to + 20V in such a configuration and taking into account that logic level Mosfets can only have +10V to -10V on their gates, we changed the circuit and realized it the old way, using relais. Since speed is very low, this has no negative effect on performance. However, the relais clicks are audible.

There still is a problem with this circuit however: fast switching from DC to AC mode causes glitches (and sparks over the relais contacts) causing faulty data in our latches... If you first perform a note off, do the switching, wait for 50ms and then switch the DC mode note on, there is no problem.

Power supply voltages and currents:

• 12V dc: required for the 50240 divider. Draws 50mA. Power supply can deliver 250mA.
• 5V dc: required for all logic boards and displays, 3A (This power supply is equiped with 3 sepate 1A outputs).
• 24V dc: required for the moving coil assembly, (3Amax), the valve solenoids (2.1A max) and the foot stepper (420mA). So we used a SMPS rated for 24V , 6.4A
• 230V ac for the radial compressor

Mapping:

Midi note range: 12 - 47.

The footstep is mapped on midi note 48. It is not required to send separate commands for the pistons, since these commands are handled automatically in our DLL code. For your information however, we can tell you the pistons are internally mapped on midi notes 64,65 and 66. The note range 56 to 63 is used to steer the power DAC. This also is handled automatically. The DC/AC control switch is mapped on midi note 70.

Note Off commands are required. Velocity is implemented and has a wide control range. Very soft notes do not sound very natural, since no real tuba is able to produce those.

Controlling the wind supply is possible by using a standard channel pressure (aftertouch) midi command.

Note that although this instrument is using a midi protocol, it cannot easily be driven with a standard midi sequencer program. However, we are preparing a software track converter to convert standard midi tracks intented to be played on <So> to the commands the instrument is expecting.

Technical specifications:

• size: base 700mm x 700mm, heigth 2200mm (For transportation, the sousaphone bell can be taken off)
• weight: ca.70kg
• power: 240V ac / 200W peak, nominal 60W.
• Tuning: based on A = 440 Hz (within 1%)
• Ambitus: midi note 15 to midi note 45 ( to 47 with carefull adjustment of playing head) (mouthpiece pulses can be generated using notes 12 to 14 and external signals can be applied using note on/off commands for note nr. 8)
• Insurance value: 7500 Euro.

Design and construction: dr.Godfried-Willem Raes

Collaborators on the construction of this robot:

• Kristof Lauwers (Standard midi to specific So-midi conversion software)
• Leonaar Degraeve (tuba advisor 2002)
• Bert Vandekerkhove (assistance in soldering)
• Moniek Darge (painting)

Music composed for <So>:

• Godfried-Willem Raes "So What" (premiered on august 21th 2003)
• Godfried-Willem Raes "GestroSo"
• Godfried-Willem Raes "SQE v STO 4 QR" (premiered on september 9th 2003)
• Kristof Lauwers & Moniek Darge "King So" (premiered january 14th 2004)

Nederlands:

Robot: <So>

In het M&M robot orkest hadden we behoefte aan wat meer variatie in de heel lage basinstrumenten, niet in het minst voor de verklanking van de opening van mijn apero <Technofaustus>. Alleen de <player piano> en <bourdonola> beschikken over een in de laagte redelijke bas. Nu is het maken van lage instrumenten op zich eigenlijk technisch eenvoudiger dan hoge vanwege de geringere eisen gesteld aan de precizie bij de bouw, maar, de afmetingen ervan swingen werkelijk de pan uit. Om midi noot 24 voort te brengen met luchtkolommen bvb., heb je gauw een bouwhoogte nodig van ca. 6 meter... Tongwerken anderzijds klinken wanneer ze klein worden gemaakt, gauw erg nasaal en uiterst boventoonrijk, waardoor ze niet goed als dragende bassen aan te wenden zijn. De bezoekers van de <M&M> koncerten zullen dit ook wel al hebben opgemerkt bij het horen van de klanken van <Vox Humanola>. Vandaar het idee om werk te maken van een geautomatiseerde bastuba. Een tuba, het instrument bij uitstek voor de verzorging van sterke dragende bassen, hadden we wel niet in onze instrumentenverzameling, maar een Sousafoon, ooit eens op de rommelmarkt gekocht voor een prikje, hing nog ergens in onze traphal sierraad te wezen. Nadere inspektie leerde ons dat het om een Sib instrument ging voorzien van 3 ventielen. Automatisering van die ventielen bleek een erg eenvoudige klus, maar het vinden van een adekwaat klankvormingsmechanisme had heel wat meer voeten in de aarde. Na heel wat research met namaaklippen in rubber, silikonen en neopreen, kleppen in koper, mica en teflon, kwamen we terecht bij een reeds in de 19e eeuw bekend mechanisme voor toonopwekking: dat van het diaphane register in sommige britse orgels. Het toongat, in ons geval het mondstuk van de sousafoon, wordt daarbij door een zachte en juist sluitende klep heel erg snel geopend en gesloten. Dat klinkt zo'n beetje zoals je met de palm van je hand op het mondstuk slaat: een zachte slaptongue op het instrument. Nu was het zaak deze klep tegen de juiste snelheid, overeenkomstig de resonantiefrekwentie van het instrument, te laten trillen. Elektromagneten bleken hopeloos te traag: we haalden nooit snelheden groter dan ca. 40Hz. Dan maar de zaak omgekeerd aangepakt: vaste magneet en beweeglijke spoel. Zo hadden we ei zo na opnieuw de luidspreker uitgevonden natuurlijk... Hier echter, wordt niet een membraan in beweging gebracht door de spoel, maar uitsluitend de afsluitklep voor het mondstuk. Dit bleek prima te werken en liet ons de mogelijkheid ook lucht opgewekt door een radiale kompressor aan de achterzijde toe te voeren. De sousafoon wordt op die wijze ook echt aangeblazen. De pedaalnoten (midi 15 tot 22) bleken met ons op deze wijze opgebouwd artificieel hoofd uitstekend speelbaar: voor menselijke spelers zijn die tonen zo goed als onhaalbaar). Alleen om snel van lage naar hoge noten te kunnen overgaan, konden we geen snel genoeg reagerend drukventiel verzinnen. De tessituur zal dus beperkt blijven tot de diepere regionen van de muziek (tot midi noot 47).

Als extraatje hebben we onderaan deze robot een houten leest gemonteerd, die bekrachtigd door een elektromagneet, de maat kan tikken op de grond; 't heeft voorwaar iets menselijks zo...

Deze nieuwe robot werd op het 21 augustus 2003 koncert van het Logos <M&M> ensemble ten doop gehouden. In de daaropvolgende weken werden nog vele verbeteringen in de werking van de robot aangebracht.

Godfried-Willem Raes

Construction Diary:

• 15.03.2001: first ideas and practical sketches.
• 12.09.2002: Proeven met rotatiemechanismen voor de klankopwekking, voortbouwend op experimenten opgezet door Christoph Schlaegel. Het probleem is het vinden van stillopende motoren met extreem hoge toerentallen en uiterst geringe traagheid...
• 18.10.2002: Principle design of control electronics.
• 01.07.2003: Design of a UART decoder for non-standard midi control in robots.
• 02.07.2003: PC board design finished and sent to Digit printservice.
• 03.07.2003: Tests and experiments with compression drivers (as used on Autosax). The sound is not very pleasing and quite electronic in nature. So this path was rejected.
• 04.07.2003: Test lucas ledex solenoids on valves (same type as used on Vibi).
• 05.07.2003: Design of sound synthesis part and vibration mechanisms.
• 06.07.2003: part placement and soldering of UART pc-boards. Testing UART boards with midi input.
• 07.07.2003: part placement and soldering of DEMUX circuit boards.
• 08.07.2003: part placement and soldering of power Mosfet driver boards.
• 09.07.2003: Welding of playing head assembly with artificial lip mechanism. (modified Sonics SLE60 moving coil operated valve)
• 10.07.2003: soldering driver boards. Test artificial mouth mechanism. Now behaves somewhat like a 19th century diaphane register in some British pipe organs.
• 11.07.2003: start construction wheelbase for <So>. Software written to calculate the valve lookup table. Artificial mouth welded and soldered. Speaker driver mounted. Procedure GetInstrumParams in g_file.dll prepared to return the correct values for <So>.
• 12.07.2003: Welding day... Basic construction, wheelchair model, completely welded together. Plasma cutter gave up... Murphy being the way he is, we also fall without argon gas...
• 13.07.2003: Mounting of sousaphone on base construction. Artificial mouth connected to sousaphone. Solenoids mounted on valves.
• 14.07.2003: Plasma machine to repair (Welda) . Argon gas ordered (A-Gas center). Frame for PC boards welded. Frame mounted (movable) in instrument base. Soldering divider synth board. Base plate holder in glasfiber epoxy cut out.
• 15.07.2003: Rescue came: Fresh Argon gas! Replacement plasma machine available... PC boards mounted on base assembly plate. Start soldering AND- mosfet driver boards.
• 16.07.2003: Piston solenoid circuit designed, using large cap and power series resistor, to limit dissipation. Practical RC values used and soldered in (cfr. circuit diagram): 15 Ohms and 4700mF.
• 17.07.2003: construction of piston solenoid board and mounting. Assembly mounted under left arm. Further soldering on note driver boards (connectors). Low level driver code added to gmt in module g_midi.inc compiled to g_lib.dll.
• 18.07.2003: power DAC circuit built and tested.
• 19.07.2003: wiring boards. Woodshoe model found on flea market.
• 20.07.2003: more wiring of boards
• 25.07.2003: design foot assembly. Wiring valve solenoids
• 26.07.2003: further wiring board assembly. Power supplies connected.
• 27.07.2003: bs2 code written for wind controller. Test program written in GMT and added to g_gorgel.exe compilation for our midi controlled robots.
• 28.07.2003: construction and mounting of foot mechanism, using a Laukhuff electromagnet. Software adapted to implement wind controller (using channel pressure command) and foot mechanism (now mapped on midi note 71).
• 29.07.2003: hardware/software debug session. 8 IRL640 power mosfets gone to heaven because of error in our software... Replaced with BUK101-50 types (moving coil drivers on latch 7). Mapping of foot mechanism can now also be on notes 48,49,50 or 51.
• 30.07.2003: design of power DAC appears to be faulty. The gates may be exposed to way to high voltages. When the mosfets have protection diodes, the AND gates will die since they will see up to 24V on their outputs... New power DAC designed used relays.
• 31.07.2003: Rescue: 74HCT93 counters found at Gentronics electronics store, so we could finish the synth board. The relais we planned to use, appeared to be bistable types. Problems finding 24V dc coil types that fit onto the sockets on our PC board...
• 01.08.2003: Bad luck day: artificial head burned out. 8 mosfets gone to heaven. So, we have to start all over again with the construction of the artificial mouth. Wiring bugs removed. Foot mechanism is now up and working.
• 02.08.2003: debug session of driver code. Specific low level code written and tested. Bug discovered in g_mus.dll: GetLowestNoteInHar and GetHighestnoteinHar had an offset error. This bug repair may affect many existing compositions. Still hardware problem with note 24. Artificial head replaced. (Sonics SLE60 driver). Wind inlet welded on the back of the head. BS2 controller programmed and placed in the circuit. So played its first notes today!
• 03.08.2003: support welded for radial compressor. Assembly of compressor finished. Polishing of valve interiors for smooth operation. Cleaning of Sousaphone. Regulating mechanism made for valves. Springs tuned. We still have problems with notes higher than midi note 30. Maybe we have to AC couple the mouth assembly.
• 04.08.2003: Those awfull holidays seem the be finally ending, so we could get the missing components again at our regular stores. 24V relais ordered.
• 13.08.2003: Zero cross relais (Crouzet type) for motor control (wind pressure) added.
• 14.08.2003: For notes higher than midi 28, AC signals work better on the mouth assembly. Transformer coupling tested. A diode appears essential now. This makes the very low notes less natural sounding however. Maybe we need a much heavier 1:1 transformer with very good low frequency response, or, a low pass filter on the output. We still have a problem with note 24. Probably a short on the PC board. Higher windpressure would also greatly improve the sound.
• 15.08.2003: 74HCT08 burnt out: this caused the failing note 24. Support added for external drive, mapped on note 8. Transformer replaced with a 50W type toroidal with burnt out 230V primary but intact split 2 x 12V secondaries. Head assembly painted red.
• 16.08.2003: very short experiment with 24:24V transformer. Seems to work better. No time today to really figure it out...
• 17.08.2003: transformer changed again. (20V:24V), series resistance should be > 8 Ohms. For good low basses it is better to use DC on the speaker, whereas for higher pitches (midi 39 and above) transformer coupling sounds better. So we will have to change the circuit with a relais mapped on note 50 to switch between AC and DC excitation modes.
• 18.08.2003: wiring AC/DC circuitry. Software extensively checked and debugged (in g_midi.inc, part of the library g_lib.dll). Our circuits still seem to suffer from inductive spikes. We may have to add many more bypass caps.
• 19.08.2003: Bypasses added. Spikes seem to remain. Trying to solve it in software. Mosfets on notes 40-47 replaced with IRL640 types.
• 20.08.2003: Rattle in compressor repaired. <So> would work better with a Laukhuff blower (tested!). Gray code based latch adressing applied. Spikes seemed to come from the inherent deficiencies of the 74HCT154 demultiplexer chips (Why does'nt our elecronics industry produce improved versions of this 25 years old chip...). Thanks to Kristofs GMT midi fileplayer, So played its first midi pieces: a Tango by Cardel and my own '2bv-2b'. We also implemented support for <So> in 'Wandering Quadrada Space'. The public premiere is scheduled for tomorrow...
• 21.08.2003: First public concert with So. It worked nicely, but in order to overcome the glitch problem we are causing a way to large midi stream resulting in a delay larger then needed. So further research is required here.
• 22.08.2003: Redesign of adressing scheme of latches. Now we should only have two bits changing on each transition.
• 23.08.2003: New wiring applied to <So>: latch adresses are now: 1,2,4,8,16,17,32,48. DLL revised. We now solved the problem with the data stream, but still have glitches on the AC/DC transitions.
• 24.08.2003: Software fine tuning.
• 27.08.2003: Ventola blower delivered from Laukhuff.
• 28.08.2003: mounting of Ventola blower in So. We have a 6dB sound level improvement now! Also, this blower is in itself a lot more quiet than the type we had mounted at first.
• 29.08.2003: construction of holding and steering bar in 3/4" tube. Painting. CEE male power socket mounted.
• 08.02.2005: UART circuitry redesigned using PIC's. This to avoid glitch problems that arrised on high midi data rates. At the same time, solenoids for valves redimensioned. In the new design we will use bidirectional types. For more recent data and follow up consult the more recent <So> page. This page is no longer updated.

Last update: 2007-07-30 by Godfried-Willem Raes