This instrument is a computer controlled assembly of five rototoms. Each drum is equiped with a set of beaters and the pitch of each rototom can be controlled. The lowest couple of rototoms have 3 beaters each, whereas the upper three suffice with two beaters each. The beaters are velocity sensitive and have a very wide range dynamic control. Heavy duty stepping motors are used to achieve pitch control of each individual drum. Instead of rotating the drums on their fixed axis, we fixed the frames of the drums and rotate the threaded axis through a geared construction using dented belts. This also contributes to more silent operation of the mechanics.
The instrument can listen to midi commands directly, using midi channel 8. However, good control of the pitches requires a lot of midi controllers to be send to the robot. The picture above gives an idea of the construction of the beater side of <Rotomoton>. The construction of two of the five stepping motors can be seen on the picture below. The picture was taken with the position sensors rermoved.
<Rotomoton> uses a lot of dedicated hardware, designed for musical automats such as player pianos, percussion instruments, organs, brass instruments, and even bowed instruments. Details can be found in our course on experimental music on this same website as well as on the detailed pages treating our other musical robots composing the Logos M&M robot orchestra.
The original version dating from 2000 used hardware based on a parallel bus controlling Intel 16 bit timer chips with a resolution of a single microsecond, next to motor controllers of our own design. It was not directly controlable using midi but required a separate laptop computer to translate midi (or midi via UDP/IP) commands to the parallel bus commands required. In 2005/2007 we redesigned the hardware such that we could get rid of the laptop. No less than 7 PIC microcontrollers now take care of the control of every detail of the mechanics. The timing resolution suffered a bit under this change and is now limited to 19.2 microseconds. An 8th PIC microcontroller takes care of the support for Midi via UDP/IP now.
The stepping motors use special circuitry, and make use of special motor controller hybrid power modules. Since in this application, very high force but no holding torque is required from the steppers, we could use many power saving features available from these motor controllers. The hybrid stepper motors used in this design are Cetronic or MAE type HY200 3424 170 A8, specified for Umax = 90V and maximum phase current 1.7A. We use them with the motor windings in parallel.
The solid aluminium dented wheels are selected as follows:
Two bits on each microcontroller for the steppers are used to read the start and end position of the tending mechanism, two bits for each drum. Miniature microswitches were first used as sensors. These may be replaced by optical or inductive proximity sensors with 0.01mm resolution later on, since our microswitches suffer from a larger than necessary hysteresis. In 2007 we experimented with inductive proximity sensors from Pepperl+Fuchs. Herewith we could obtain a hysteris of ca. 30µm. The sensors are now connected to two analog inputs on the PIC. For precize positioning, it is mandatory to reset all motors first to the lowest and next to the highest end position prior to running music compositions. This calibrates the pitch range for each drum. Software to handle this automatically has been integrated into our <GMT> language (also part of our GMT midi-file player for the M&M robot orchestra). Technical exploded drawing showing the construction of the tuning mechanism driven by the stepping motors:
5. The power supply for this instrument is rated for 1130Watts. Three
transformers are used: 230V/12V - 630VA and 230V/2x35V 200VA. and 230V/24V
- 300VA. During normal operation however, power consumption is reduced
to ca. 150VA.
Midi implementation and music:
If you are using <GMT> under Power Basic, you can use all specific hardware control functions and procedures provided in our libraries. However, direct midi control is also possible from any decent sequencer. (We use Cakewalk or Sonar, written by Twelve Tone Systems). The midi and hardware mapping of the different components of <Rotomoton> is:
Composers that wrote pieces for <Rotomoton> sofar, include: Godfried-Willem Raes ('Rotstuk' voor Rotomoton), Michael Manion, Moniek Darge, Kristof Lauwers, Rene Mogenson ('The swarm breaks through the net'), Claude Coppens. Rotomoton is a fixed member of the M&M ensemble and as such also performs in orchestra pieces such as 'Technofaustus', 'Gestrobo', 'Picrada', 'STOvSQE4MM' , "Quadrada", "g_tech611" .. by Godfried-Willem Raes and many other pieces.
Insurance value: 19.000 €.
Construction of this automated instrument started august 2000 and was completed in its first working version around easter 2001. Rotomoton played its first scales on april 26th of 2001. It is now a permanent robot member of the Logos <M&M> ensemble. Its hardware was completely revised and rebuild in 2007.
The picture on the left shows the first step in the construction of <Rotomoton>: the assembly of the five rototoms in a TIG-welded frame.
The final instrument is shown on this picture:
The <Rotomoton> automat can be heard on the Logos Public Domain CD <Automaton> (LPD007).
aim:1. improving pitch change speed by increasing torque from stepping motors.
In the original design we used unipolar steering of the stepping motors. By using bipolar drives, the torque can be increased with a factor 4 compared to the first version, where considerable power got lost in the series resistors. We decided to use Intelligent Motion Systems (IMS) stepping motor drivers, type IB106, each capable of delivering currents up to 6A and able to cope with voltages from 24 to 80 Volts. (Cost: ca. 350 Euro/piece) . For the motors we use in this robot, we could easily increase the power supply voltage to 48V and thus achieve high rotational speeds with high torque. So for each stepper, we used a single IB106 module, controlled from a PIC (18F2525) directly. The timing requirements for the motor driver are:
In the first design we had five microswitches to sense the lowest possible position for the stepping motors. No sensors were foreseen for the highest possible position. This was dictated by the fact that on a standard PC printer port, there are only 5 bits free for input. Since we do not have this limitation anymore using a PIC design, we now fitted rotomoton with end position sensing microswitches as well.
aim 2: changing control such as to get rid of yet another Windows laptop, by controlling rotomoton directly via midi commands and optionally midi via UDP/IP.
aim 3: Increasing the dynamic range of the instrument. This involved merely increasing the power supply voltage for the solenoid drivers to ca. 75V. The pulse generation can be confined to a separate PIC controller.
By also using PIC microprocessors for the steppers, we could at the same time make the robot listen to midi commands directly.
The five boards for motor control we now use were build after the following schematic:
Some sections of the circuitry do not apply to Rotomoton, since the board was designed such as to replace similar functions in our <Flex> robot as well. The power supply section had to be completely revised also. We kept the hefty 12V/630VA transformer since it was required for the brigth lights on <Rotomoton>. In the new version dimming becomes possible, since they use PWM on their supply voltage. Note the absense of a smoothing capacitor on its power supply. As a whole, the power supply is clearly overdimensioned now, since the bulbs will draw at the most 200W of power. The solenoids for the beaters get their power from a separate 70V ungerulated power supply using a toroidal transformer. For the stepping motors, an extra 24V /12A transformer is connected in series (after rectification) with the already present 12V supply. The unstabilised voltage available for the motors thus becomes 50V. With all motor activated this voltage may collapse to 44V.
Board layout for the five motor control PIC-micro boards:
On the left picture below, we see the new five motor control boards and next to it the new midi-hub board.
Last updated: 2017-08-05 by Godfried-Willem Raes
Maintenance, research and repair logbook: