an automated suspended drumkit

Godfried-Willem RAES


under design and construction

[Nederlandstalige versie]

Robot: 'Per'

In January 2018 we got a request from the Speelklok museum in Utrecht to make some of our robots available for a long running exhibition on musical robots. The robots they wanted to borrow were <Aeio>, <Bello>, <Bug>, <Pos> and... <Simba>. The loan came in as a perfect fit for the 50th anniversary of Logos. However, this placed us for a serious problem, <Simba> being used in an awful lot of orchestrations for our robot orchestra. Thus we decided to isolate the most frequently used components found in <Simba>, the hi-hat and the bell-rattle (tambourine) , and started designed a new robot that could replace these components and add some extra features as well. Thus <Per> was designed such that it could for the most part replace both <Simba> and <Troms>, a minimal drum kit as it were. As we are running out of space at Logos - at the time of this writing, the robot orchestra consists already of 72 musical robots - we decided to make it a robot to be suspended from the ceiling. Hence, it should not become too heavy. The idea of a flying drum kit also inspired us to develop a special Namuda production around it, to be premiered at the occasion of the festivities for the 50th anniversary of the Logos Foundation in our homebase in Ghent..

Here are some selected components:

For the tambourine we used 16 brass shell bells from an old orchestral tambourine dating from the beginning of the 20th century. In fact, the same shells as used for the <simba> robot. The design, although entirely new, follows the lines of the original instrument. Also we found back a small set of four Latin percussion drums we once got as a present from a girlfriend: As these are miniatures, although very well made, they produce very high pitched drum sounds. The kit consists of a small conga, a darbukah and a pair of bongos. Designing a good sounding beater mechanism for these tiny instruments was not a trivial matter. The beater mechanisms we used hitherto didn't work very well and certainly couldn't compete with what human hands and fingers can produce. It's also worth to note that these drums use pretty thick natural skins and thus require quite some striking force. The best results we got after long experimenting sessions, was using flat blade springs as beaters. These springs we made from old metal saw blades. As the blade springs have to hit the drum membrane in a perfectly flat way, this idea can only be applied to drums not having a rim over their circumference. So it would not be applicable in a robot such as <Troms>.

The bass drum used here is in fact the other half of the bass drum we used for the <Troms> robot : The cymbals were more of a problem as we did not have a pair of decent cymbals with equal diameters in stock... For the movement of the cymbals on the hi-hat mechanism, we found a heavy duty solenoid type - presumably made by Siemens - , but the anchor was missing. So we made new anchor from very thick polished steel tube, in fact a recycled part from an old photocopier. The hi-hat assembly using these solenoids came out to look like this: To operate well, these solenoids require pretty high voltages. However, at 100% duty cycle the voltage must be limited to 40 V, as we found out by measurement (temperature rise over a long time in function of applied voltage). Thus we required a microprocessor controlled high voltage power supply. To keep things as simple and reliable as possible, we used a zero cross optical relay -internally using a triac - driving a rectifier and a quite hefty electrolytic capacitor.

This is the principle, drawn as a circuit diagram: We revisited an old and proven but quite primitive circuit principle: This is pretty easy to implement on a PIC controller, as long as the control pulses are longer than a full period of the mains frequency, 20 ms. Due to the long RC time realized with the large capacitors, we can go with very slow pwm. The solid state AC relay we used is MP240D4, as it's a zero-cross relay specified for 4A at 280V ac. The feedback-loop for voltage regulation makes use op an optor, a resistive optocoupler. Instead of the pulse transformer driving the IGBT, an optocoupler can be used as well, but this requires a separated power supply, unless an esoteric high voltage optocoupler is used. Note bthat there always must be a load in this circuit, as otherways output voltage will always be the peak voltage of the input.

We invested quite a lot of research time on the beater mechanisms used in this robot. First of all we wanted to improve on the beaters as we made them for <Troms>. The problem with Troms, using Laukhuff pallet valves for the beaters, was that the dynamic range goes down with decreasing size of the drums. Here we wanted to get a much more penetrating sound. As said above, we found that flat blade springs perform better in this respect than striking mechanisms using a ball. However for the bass drum, we went a very different way and here we used solenoids with a fully free anchor. These behave very different than standard push or pull solenoids. When activated, the anchor moves to the magnetic central position and moving it from there requires a force proportional to the distance of the movement, up to half of the length of the anchor. So the behavior is a bit spring-like. When activated with the anchor one fourth of the length out of center, the anchor moves through the coil with an overshoot and then returns back to the central position. It's exactly this overshoot we use here for striking the drum. A light spring is used to return the anchor to an out-of-center position after a stroke. Without such a spring, further strokes would be impossible as the anchor wound start from the central and forceless position. The big advantage of this mechanism is that it guarantees an elastic stroke, as the anchor with the attached beater is basically free during the collision with the membrane of the drum. It goes at a price however: repetition speed is limited by the large inertia of the anchor and also, power efficiency is quite low. Mostly for visual reasons, we wanted the drums in a vertical position although from a pure functional point of view, a horizontal position would yield much better results and has the advantage that a return spring would not be needed and that friction would be minimized.

The firmware for all PIC microprocessors was written in Proton Basic.

Firmware for the midi-hub and power board per_hub.bas per_hub.hex
Firmware for the pulse-hold boards per_beat.bas per_beat.hex


Circuit Overview:


to be worked out, such as to have maximum compatibility with <Troms> and <Simba>

Midi implementation:

The midi channel for <Per> is 6 (0-15) or 7 (1-16).

Midi note range: 24- 100., Velocity implemented to steer the attack force of the beaters, the hi-hat and the tambourine.dividual note aftertouch (polyphonic) under development.

Note Off commands are not required for the drums, note release is not implemented. Note off is mandatory for the tambourine and the hi-hat. If you leave them on for too long, the solenoids get very hot.

Key pressure is implemented for automatic note repeats. The pressure value determines the repetition speed. Maximum repetition speed is 16Hz, but if such fast values are used, velocity values have to be kept at very low values. It is obvious that when the repetition length is shorter than the velocity pulse length, repetition will not work. Also, note that repeats using key pressure are 'sticky'. The setting is not canceled with a note off. So, once set all new note-on commands will lead to repeated notes, unless key pressure is set to zero again.


Controller #30 is used to set repetition speed for all notes to one and the same value. The parameter determines the repetition speed. (Range 2Hz to 16Hz for values from 1 to 127). Repetitions start on reception of a note-on command. Thus, phase shifts of the repetition frequency will occur if notes are not started at the same time. This controller, with value 0 can also be used to cancel all repeats.

Controller #66 is used to switch the robot on or off. Switching the robot off, resets all controllers.

Controller #123: <Per> responds to the midi all-notes-off command. This command also switches off the lights.

Technical specifications:

Design and construction: dr.Godfried-Willem Raes (2018)

Collaborators on the construction of this robot:

Music composed for <Per>:

Back to Logos-Projects page : projects.html Back to Main Logos page:index.html To Godfried-Willem Raes personal homepage... To Instrument catalogue Naar Godfried-Willem Raes' homepage


Robot: <Per>

Er is geen Nederlandse beschrijving beschikbaar. Zolang we geen strukturele erkenning krijgen van de Vlaamse Gemeenschap zal daar ook niet meer aan gewerkt worden.

Building logbook Bouwdagboek
Following diary given an idea of the work involved in the making of the <Per> robot. It also illustrates the building process.

Omdat ons vaak wordt gevraagd hoeveel werk en tijd kruipt in, en nodig is voor, het bouwen van dergelijke muzikale robots, houden we ook voor <Per> een beknopt en geilllustreerd bouwdagboek bij:


To be done

Robodies Pictures with <Per>:

none as yet.


(Terug) naar logos-projekten:


Terug naar Logos' index-pagina:


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Last update: 2018-05-21 by Godfried-Willem Raes

Technical data sheet and maintenance instructions:

board output connector pin mapping wire color remarks PIC pin Weidmueller
1 2     pulse/hold 4,3 4p1
2 3     pulse/hold 2,5 4p2
3 4     pulse/hold 6,7 4p3
4 5     pulse/hold 8,9 4p4
5 7     pulse/hold 10, 37 4p1
6 8     pulse/hold 36, 35 4p2
7 9     pulse/hold 34, 33 4p3
8 10     pulse/hold 30, 29 4p4
9 12     pulse/hold 28, 27 4p1
10 13     pulse/hold 24, 23 4p2
11 14     pulse/hold 22, 21 4p3
12 15     pulse/hold 15, 16 4p4
13 17     pulse/hold 17, 18 2p1
14 18     pulse/hold 19, 20 2p2

Parts & components:


Disassembly and servicing instructions:

This robot uses drums with mostly natural skins. Hence it has to be protected from moisture.

Cost Calculation for this building project:

Item - Qty. specs. cost
6 m stainless steel 50 x 5 310,-
2 m stainless steel 30 x 3 73,-
1 m2 stainless steel 3mm thick, plate 245,-
1 Latin Percussion miniature drumset (4 drums) 110,-
1 Regular turkish Darbukah 40,-
1 miniature darbukah 25,-
100 M3 hex-cylinder bolts 35,-
100 M3 stainless steel nuts 25,-
100 M4 hex-cylinder bolts 40,-
100 M4 stainless steel nuts 35,-
1 3/8" threaded rod 17,-
5 3/8" brass nuts 15,-
4 Sandvik steel sawblades 10,-
1 Funke electric bell (for mechanism) 24 V 50,-
10 Laukhuff pallet valve solenoids 585,-
2 Siemens open solenoids 1A / 60V 140,-
1 Blacknigth pull solenoid 24V 65,-
1 Brass shell tambourine - brass shells 22,-
1 set of 2 hihat cymbals 255,-
1 soft steel rod, massive, 17 mm diameter, 300 mm long 11,-
1 wood handgrip, lathe turned hardwood 2,-
10 hardwood wood balls, 20 mm diameter 10,-
6 m stainless steel tube, 50 mm x 2 mm 80,-
2 stainless steel brackets 46 - 54 mm 24,-
10 felt rings, Laukhuff 17,-
1 spring, diameter 22 mm, 100 mm long 3,-
1 bass drum, Pulse Percussion 120,-
20 M10 stainless steel cylinder head bolts 60,-
25 M10 stainless steel nuts 25,-
12 shock absorbers 72,-
1 stainless steel flange, diameter 160 mm 27,-
1 Argon gas cylinder 120,-
  Welding electrodes 175,-
1 IEC mains entry block 8,-
1 Power switch 12,-
1 M16 nut, stainless steel 3,-
10 cutting discs 0.8 mm 14,-
1 16 mm drill Cobalt 12,-
1 10 mm drill Cobalt 8,-
  TOTAL (expended sofar) 2900,-

On the original budget but not yet expended:

nr description
1 ride cymbal or ice bell
1 Hub PCB
1 pulse PCB
3 Power supplies
2 motors
2 propellers
  sensing components
1 safety transformer and suspension gear
from stock
6 lights
from stock
  TOTAL: (first estimated total)


calculation based on 273 Euro/day, which is the wage cost derived from our payrolls in 2017.

(Invoiced by self employed collaborators Bert Vandekerckhove, Johannes Taelman a.o.)

days task
? design
pro memorie
3 firmware design
10 welding and mechanical assembly
2 testing and adjusting

Total estimated cost: 9.388 Euro