Mechanics 2
The MR-808 robotic HiHat
The HiHat machine is part of the Drum Robot MR-808. It took some experiments until I figured out how this can be crafted into a high-performance working instrument: A HiHat is normally used in any track and plays most of the time!
This robotic HiHat is based on a normal drummers hihat, with two cymbals and parts of the hihat-stand. It also contains two solenoids (electro magnets), one for opening and closing the cymbals, on for the actual beating of the cymbal.
The force needed to open the HiHat is quite high, as it has to work against the force that closes the HiHat. The solenoid used here comes from a car engine starter. They have the most powerful solenoids, are reasonably cheap, easy to get at any car junk jard (or eBay) and operate at 12V. Perfect for low budget robotics!
The disadvantage is, that they consume roughly between 30 and 50A. Un-technically spoken: This is very much! I use server power supplies which can supply a current up tp 50A@ 12V.
I started with a standard HiHat machine (the full hardware Hihat Stand) and cut the lower part off. One thing you have to consider: a HiHat is default-OPEN, meaning that the spring inside keeps the cymbals separated when no pressure is applied. Only if the drummer steps on the foot-part, the HiHat closes. Replacing the drummers-foot with a solenoid (yeeha!) would mean that you would have a constantly powered solenoid, in this case about 35A, for most of the time (closed HiHat).
As we don’t want to fry eggs with the robot (solenoids can get quite hot) its recommended to reverse this mechanics, meaning that the HiHat is default-closed, and the solenoid is only powered when you want an open HiHat. I then removed the spring and let the gravity do the closing of the cymbals. Afterward I attached a fan inside the HiHat machine as the solenoid gets really hot for off-beat disco music. The huge car solenoid is only for the opening and closing of the hihat.
The actually beater is another solenoid which just hammers directly on the lower cymbal. It is used for both closed and open HiHat.
MR-808 Interactive – Technique
Collaborative drum sound installation: decovering digital action & physical reaction
The drum robot installation MR-808 as it exists gives an immediate feedback on how the sound is created. The listener can see the sound physically evolving from the robots.
The drum robot is controlled via a web interface by users with tablet computers. The audience can program the drum robot in a collaborative process and listen to and see the emerging sound in real time on the exhibition site.
Background
In November 2012, the “MR-808”, a huge robotic drum machine installation, wasreleased, developed under the direction of Moritz Simon Geist. The drum robot, build after the famous TR-808 has so far been presented on various events, from techno club nights to media and hacking congresses.
The robot installation MR-808 is a replica of the famous 1980s electronic drum machine TR-808, with robots playing the drum sounds! For the Installation MR-808 eleven sound of the 80s drum computer TR-808 are replaced by mechanical actuators and physical tone-makers. The actors are placed in a 330 x 170 cm size replica of the original drum machine. The robot installation visualizes the motion and formation of sound creation in a way no other tool of electronic sound creation is able to.
Program beats together, in a Browser!
The idea was to have a universal interface with which the average everyday person can program “moderated beats” – a step sequencer – with an interface they already know. We choose Nexus 7 tablets because they were reasonably cheap and esay to use. The interface itself consist of a basic step sequencer which is quickly comprehensible.
- Server running on a Raspberry Pi
- Node.js and SuperCollider
- Javascript for the interface
The Colaborative Sequencer is a web-based MIDI sequencer application. The server runs on a RasperryPi (Model B) rendering an node.js based interactive website and is connected with websockets. Different clients can connect to the server, manipulating a SuperCollider Step Sequencer (also running on the RasPi). A midi-interface connected to the RasPi outputs the Midi note whoch then go to the MR-808 to trigger the different instruments.
Special care has been taken to control the latencies of the different instruments. Each robotic instrument (Snare, Bass Drum…) has its own unique latency, given by the time between the “note on” signal (triggering a note in the sequencer), and the time when the tone finally leaves the physical instrument. These latencies can be up to several 100 microseconds, a delay that a human ear will definitely recognize. The latency consists of the time for the physical path that the actor has to resolve to get to the instrument and the electrical and digital delay inside the electronics and software. Read more about it here.
Resources
We try to open-source all the technologies used. If you have any questions, contact us.
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