2000-2002-2006-2010, 2017
Version 2.2

automated nature sounds
Godfried-Willem Raes

This instrument is a computer controlled assembly of percussion and 'effect' instruments. All sound sources incorporated in this instrument are non-pitched and share a vague reference to nature sounds: we encounter thunder, rain, woodpeckers, wind, a bird, storm, lightning, crackling wood, squeaky sounds... In this respect it could be considered a realization of the first category of sound sources in Luigi Russolo's Intonarumori. Also soundwise, this futurist reference is pretty obvious. A bird was donated by Moniek Darge, and lives since on a little piece of grass underneath <ThunderWood>. It got company from a sounding cricket in 2006.

The instrument can be played by standard MIDI commands, using commercial sequencers or our GMT software but is also capable of listening to pure algorithmic commands.

The first working version of this instrument was finalized on July 18th of 2000. Later, the lightning was added. The storm-wind module, as well as the bird sound, was designed and finished in august 2002. Thunderwood has undergone a complete revision in 2006, whereby it can be controlled by midi directly. Some light effects, as well as the squeaky sounds were added in 2010. High resolution pictures are available on request.

<ThunderWood> was originally made and designed to be a part of the <Slag-Werk> project realized by Godfried-Willem Raes for 'Web Strikes Back' at the occasion of the Tromp biannual, October 2000 in Eindhoven, the Netherlands. It is since a standard robot component in the Logos Robot orchestra.

Technical details:

The <ThunderWood> robot uses dedicated hardware, designed for musical automata such as player pianos, percussion instruments, organs and even bowed instruments. Details can be found in our course on experimental music as well as in the descriptive webpages on our many other robots on this same website. A general article 'Expression Control in Musical Automates' covers the many aspects of the design in depth.

The hardware for <ThunderWood> consists of following components and printed circuit boards:

1. a midi input/hub board, housing a single PIC controller (18F2525 type) in charge of the motor driven components and the heavy bi-directional solenoids used for shaking the brass thundersheet and the bamboo wind chimes..

2. A pulse driver board, using a PIC microcontroller, type 18F2525. This PC board houses the power MOSFETS used to steer the solenoids used for activating the one-shot sound sources. (Woodpeckers, bird, cricket).

3. Squeaker and LED light control board. This board uses another 18F2525 microcontroller taking care of the PWM control of the two squeakers as well as the high power LED lights. This board makes use of high side drivers using P-channel power MOSFETS. The circuit is build as a stand alone unit with its own integrated power supply. The circuit looks like:

The physical circuitry as well as the sound mechanism mounted on the base of the automate look like:

There are 4 woodblocks in the instrument, each provided with a number of solenoids driving the beaters. The lowest woodblock has 5 beaters, the second lowest 4 beaters, the second highest 3 beaters and the highest block got only 2 beaters. The woodblocks are handmade from dark tropical wood and hollowed out. The slit, also functioning as a cavity resonator, is underneath the blocks.

In addition the instrument has as set of low sounding bamboo windchimes, the latter are activated the same way as the brass thundersheet, suspended in top of the instrument..

A wind-machine was added to the instrument also. This engine uses a strong DC motor (700W / 12V - 210V DC) since this made precise speed control easy to implement. The motor rotates a perforated stainless steel cylinder taken from an old laundry machine. Over the cylinder a piece of heavy canvas hangs, causing the wind-noise production proportional to motor speed. In the picture to the left, the canvas is removed to better reveal the mechanism. The motor is controlled using one of the hardware PWM outputs available from the PIC controller. Kevlar, polyester or Tyvek, or even architects paper may be used instead of canvas to produce the wind noise. All of these materials wear out after intensive use and should be replaced regularly for a good sound.

A ratchet , controlled by a synchronous AC motor with speed reduction mechanism (gear box) makes the crackling wood sounds in this instrument. As can be seen from the picture, the wood tongues are taken from an old metric size. This device is switched on/off via a relay.

A rainmaker was implemented by filling an RCF 300Watt loudspeaker [a 20cm woofer with glassfiber cone as used in RCF's Monitor 8 enclosures] with fine grains or pellets. The speaker is mounted underneath the instrument. Over the speaker we mounted a resonator taken from a Turkish darbukkah drum. [cf.. picture] This resonator is mounted upside down. The assembly is placed such that the cone is horizontal. The speaker is driven just as if it were an ordinary solenoid and causes a rain sound when driven with a series of slow pulses. To damp any remaining speaker noises (caused by the square waves) be did provide a simple LC low pass filter (cut off frequency at 77 Hz). Maximum allowable DC current through the speaker coil should be limited to 1.5A at 12V maximum. With the low pass filter, we can power this part of the circuit from 45V directly. Needless to say that the capacitors in the circuit as shown need to be bipolar types!

4. The power MOSFETS we used for controlling these solenoids are Harris RFP10N12L (or the more modern equivalent IRL640), since these switch on TTL levels and are capable of dissipating 60 Watts. Cooling is not required, since the current flows only in bursts for very short times. The current rating is 17A and their Uds limit is 200 V. The rather high gate capacitance (1200 pF) 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 it is impossible to operate the instrument before sending the required power on/off command (midi controller 66).

5. The Storm component of <Thunderwood> was realized with a small cavity resonator coupled to a linear cone made off brass. The fan used (Rotron Manufacturing Corporation) to implement it was taken from an old aircraft and hence its motor runs off a 3-phase 208 V at 400 Hz frequency power supply.
We designed a 3-phase generator using a 16-bit PIC 24EP128MO202 motorcontroller to generate the required voltages. The speed of rotation can be controlled by sending the velo byte that goes with a note on command. Note that suction wind is used , and therefore the horn and the cavity resonator are mounted on the side of the fan. The strongly one-directional windflow from the blowing side does not yield good musical results! Cavity resonators work best when driven with a highly turbulent airflow. The original circuit was replaced in 2017 with this new design, wherein we implemented some new features, such as braking, controlled by the release byte of a note off command:

This is what the physical board for this circuit looks like:

5. For the DC motor controlling the wind machine, one of the hardware PWM's provided on the 18F2525 on the hub board PIC is used. This motor (a Thomson brushed DC type) runs off the unstabilized 35 V power supply thus limiting the maximum speed to safe values. Of course here also a power mosfet is used in a conventional DC motor control arrangement.

6. The bird sounds were added to <ThunderWood> in august 2002. The mechanism uses a small pump driven by a solenoid. The bird sound is produced by a special anticonical high pitched organ pipe. A mechanism making use of a threaded rod passed and rotated through a piece of hardwood, driven by a DC motor with speed reduction gears, was realized in a first attempt, but needed too much maintenance (rosin!) to be reliable in this automate. The pump mechanism implemented now, uses velocity control for the air burst, but cannot make long sustained sounds. The solenoid used is a Lucas Ledex type, as used in our player piano. It is connected to the 48V power supply. The return spring is build into the pump. This mechanism served as a prototype for <Puff>. The bird itself, a mere visual feature, is a donation from Moniek Darge...

7. Cricket: this sound source was added at the occasion of the complete revision of the <ThunderWood> electronics in 2006. The mechanism is a modified small motorbike horn with a metal membrane. It does not produce a realistic cricket sound, as it is way too loud (imagine a fff cricket of a prehistoric kind...), but can very well be used for short click sounds. It is mounted above the solenoid driving the wind chimes.

8. As an extra (visual) feature during the rebuild in 2006, we added an orange rotating flashlight, reflecting on the thundersheet. This light can be controlled with midi controller 70.

9. The power supply for this instrument is rated for 650 Watts. Thunderwood was not designed for mobile use and therefore cannot be operated from batteries.

The power supply is kept very simple and consists of three hefty building blocks, mounted on the base of the automate on the right and the left side. Two small size SMPS modules take care of the required +5 voltages for the processor boards. Note that this power supply delivers a bunch of different voltages. Very thick wiring was used for the lower voltages since we are dealing with pretty high currents here. (At times up to 20 Amps!). The somewhat strange looking power supply with the toroidal transformer can be explained because we modified an existing Velleman power amplifier supply with split voltages, to serve for this new purpose, by connecting both windings in parallel. As the capacitors in 2012 exploded, we changed the circuitry and disposed of the original circuit board altogether.


Any decent sequencer program can be used to write and edit music for <ThunderWood>. We favor Sonar (the new name for Cakewalk). If you are a programmer-composer and using <GMT> under Power Basic, you can use all specific hardware control functions and procedures provided in our DLL libraries. A midi command converter was written in <GMT> by Kristof Lauwers and the author. A plugin usefull with just about any sequencer was written by Alain Van Zeveren in 2021. The midi mapping and implementation is as follows:

Midi mapping:

All commands have to be send to the <Thunderwood> midi channel: 5 (0-15) or 6 for those who count 1-16.

Program change 0, 122-127 select different velocity lookup tables applicable to the woodpeckers and all other sound generating devices except the squeaky sounds. The velocity scaling lookup tables can be programmed using sysex commands. 0 is the original, non-reprogrammable mapping. It is recommended to always use 122, which contains an optimized mapping.

For those preferring to see the mapping in 'staff' notation:

Sound Samples:

Compositions for <ThunderWood>:

Collaborators on this project:


Insurance value: 9.500 Euro.

Note for organizers: this instrument is very high and cannot be mounted lower than the height given. Make sure the space you provide allows for the height of this instrument: 3.2 meters. During transportation, the upper part can be taken off, such that transportation requires a van with an internal height of only 1m65. <ThunderWood> is mounted on 4 autonomous wheels with brakes, so it can easily be positioned and repositioned. However, the automate should never be put flat but always stay in a vertical position. <ThunderWood> is not suitable for open air performances, since the electronic circuitry is fully exposed and not weather protected.

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The <Thunderwood> robot can be heard on the Logos Public Domain CD <Automaton> (LPD007).  as well as, in combination with many more automatons, on LPD008 <M&M>, a CD recorded by the Logos Robot Orchestra.

Last update:2022-06-12


Repair and maintenance notes:
Components, references & relevant data-sheets:
IR2104 H-bridge driver
IR2104 application notes
BUK454 power MOSFET, data sheet
IPP200N25N3G, MOSFET datasheet
IPP60R180C7XKSA1 datasheet
Firmware for the PIC 24EP128MO202 microcontroller (storm module) : source code , hex-dump
Firmware for the PIC 18F2520 microcontroller (Squeaks board): source code, hex dump