by Godfried-Willem Raes
The central part of this computer controlled musical automaton, made and designed in the year 2000, is a robust free standing module containing all the control electronics, microprocessors, the power supply and three automated instruments: 2 shakers (maracas) and one large siren. The design of this module resembles an altar piece, maintaining strict symmetry. The central part is formed by the motorized and belt driven heavy duty siren. In top, a large voltmeter reflecting the electrical state of the instrument. Voltmeter and siren are covered with an arc made of stainless steel.On the backside of the voltmeter, a rotating blue flashing light is mounted. From the underside of the instrument we see a row of six XLR connectors. Here the wires feeding the <Springers> originate. These <Springers> are a computer controlled assembly of maximum six free standing percussive instruments using very large springs. All spring sound sources incorporated in the <Springer>-instruments are highly reverberating and can be placed, far away from the control unit, freely in a large space. In suitable spaces, the springs can be suspended, without using their tripods, as well. In all cases, the springs end on large resonators made from stainless steel and hardened brass, placed on the floor on special adjustable stands. The automate was designed to be pretty monumental since it had to fill the forum of the Technical University in Eindhoven, a space with a very high ceiling.
The instrument can be played by standard MIDI commands and a midi implementation table is given further below on this web page.
The picture to the right is a detail of the top part of the tetrahedral structures from where the springs are suspended. The large cylindrical object is the hefty solenoid activating the springs.
Six of these components form the top vertexes of six tetrahedral structures with legs ranging in lengths as shown and chosen from the table below:
The springs were in the original version (2000) attached to large empty oil barrels (200 liter, for the largest selection of leg lengths, for the smallest selection, 100 liter) serving as amplifiers. For one of the springers however, we constructed a resonator from an old circus bass drum, by providing it with a single brass membrane to which the spring is attached. The resonance of the latter construction was so much better that we replaced the oil barrels for all the other springers with similar resonators using hardened brass in 2008. Since we had no more metal bass drum bodies available, we constructed the flanges from stainless steel. This greatly improved the sonic result and it also made transportation of the entire instrument a lot less voluminous and cumbersome. The legs for each one of the springer-modules are made of 3/4" gas tubing, reinforced at the slotted ends. These legs have steel feet such that they are stable even on very polished and slippery floors. If placed in open air, on ground or grass vegetation, the feet can be left out of the set up.
The instruments were originally made and designed to be a part of the <Slag-Werk> project realized for 'Web Strikes Back' at the occasion of the Tromp biannual, October 2000 in Eindhoven, the Netherlands. In that project the installation was controlled by the internet: people could submit playing instructions to the automate from anywhere in the world. Audio feedback to the participants, using webcasting, was implemented as well.
The <Springers> use dedicated hardware, designed for musical automata such as player pianos, percussion instruments, organs and even bowed instruments. The first version of <Springers> used a laptop computer for controlling the different components of the instrument. In 2006 we revised the instrument such that it since than can take midi input directly. It has a couple of microcontrollers taking care of all electromechanical controls.
The hardware in the control module consists of a single board carrying the PIC microprocessor and a few more circuit boards for the different power supplies required.
The power Mosfets we used for controlling all solenoids are IRL640 , since these switch on TTL levels and are capable of dissipating 60Watts. The current rating is 17A and their Uds limit is 200V. The rather high gate capacitance (850pF) is not a real problem since switching speeds in this application are inherently pretty slow. For this reason we did not fit a resistor between gate and ground in the driver circuit. Note that when the power supply is switched on, all PIC outputs may go to a high state, thus sounding all springers at the same time. To avoid this, users should always first switch on the 5V power supply and only when the PIC controller has started up, switch on the high voltage power supply for the solenoids. Hence the dual switch in the power supply.
The power supply for this instrument is rated for 440 Watts. It consists of different sections:
For the <Springers> we used solenoids made by Laukhuff, Weikersheim, type number GL90A/15. Officially these are rated 24V at 1.41A. At these conditions, they deliver a power of 55N. Anchor displacement is 25mm and cannot be modified. We took the solenoids to the lab, and derived following table describing operational conditions relevant to our application:
The springers are connected to the control module with long cables ending in female Neutrik or XLR connectors. For the largest springers, mapped on notes 120, 121,122 and 123 we used XLR-LNE high voltage types wired as shown.At the first revision of the instrument in 2006, we added outputs for two more springer elements mapped on the notes 118 and 119, but since the original type of connector XLR-LNE (produced by Cannon and Neutrik) is no longer in production, we used for these outputs two normal female audio type 3-pole XLR connectors. On these the solenoids are connected between pins 2 and 3. Ground or pin 1 is connected to the chassis but not used nor connected on the solenoid side. The female connectors are situated on the underside of the control module. Activation repetition rate is limited by the solenoids in combination with the spring-loads. Maximum pulsing frequency is about 65Hz. Of course fast repetition rates are only possible when using small values for the velocity byte.
The <Shakers> use bi-directional solenoids of the same type as we used in <Thunderwood> for the thundersheet as well as for the bamboo windchimes.
The siren is driven by one of the hardware PWM programmable pins on the microprocessor , and uses a strong DC motor. This motor drives the siren through belts. The motor belt wheel is 40mm, whereas the siren wheel measures 140mm. For safety reasons we limit the speed of the motor by using 70V dc as maximum voltage. The motor when driven with 210V dc rotates at 7000 rpm. Not only would the siren turn dangerously fast, but also -since sirens have sound output proportional to pitch- it would become largely over 120dB in loudness at an earpiercing pitch...
For the rotating flashlight, requiring 24V at 3A for full speed operation, we used the second PWM programmable PIC controller pin in a very similar way. To power this part of the engine, we used a standard switched mode power supply made by Sunpower and rated for 24V at 3.5A.
The wiring to and from the PIC controller board looks like:
Program change: 0, 122-127 select different velocity lookup tables. The velocity scaling lookup tables can be programmed using sysex commands. 0 is the original, non-reprogrammable mapping. It is recommended to allways use 122, which contains an optimised mapping.
Wave samples (click to play or download):
Concerts where <Springers> could be heard:
The sketch shows the way the shaker solenoids are connected to the shakers. Underneed is the axis of rotation (8mm). Ca. 30mm above this point another pivoting point forms the actioning point . The last pivoting point is drilled laterally through the anchor of the solenoid. The picture shows the final realization.
Insurance value: 11.750 Euro.
Note for organizers: these instruments are very high and cannot be taken into parts. Make sure the space you provide allows for the height of this instrument. Also access routes to the space have to be carefully checked beforehand. <Springers> are collapsible and can easily be positioned and repositioned. This project is suitable for open air performances, since we can put small umbrellas over the top ends of the tetrahedrons. However, this project cannot be battery operated, so mains voltage is required. For transportation, a truck capable of taking a load of 6m20 in length, is required. Springers can also be set up as an audio art installation, with radar based audience interaction. If required we can consider modifying the space requirements, heigthwize.. If the springers can be suspended from a strong enough ceiling, we can also suspend the springer modules thus reducing transportation requirements to a normal small truck without elevator.
Maintenance and repair logbook:
Technical notices & maintenance information
- 4 x RVS boordring 508 x 3, AISI 304L (Source: Demar-Lux bvba)
- 2 x RVS boordring 406 x 3, AISI 304L
- 2 x RVS boordring 323.9 x 3, AISI 304L