Photo: Jürgel Lösel

I wanted to build a mechanic hand-clap robot for the installation MR-808 that sounds like a TR-808 clap. The TR-808’s clap is infamously snappy, punchy and broad. To tell the truth: I did not really reach the classiness of the original. But it still sounds similar. First of all let’s have a look at the original circuit:
In the circuit (click on the link above to see the circuit) we can see the signal called “noise” coming in from the left side (fun-fact: the TR-808 has one main generator for white noise which is constantly on and feeding a bunch of instruments!)
The principle of the rest of the circuit makes is easy to implement it into mechanics: the noise is shaped with two VCAs, one is imitating clapping hands by applying an envelope with multiple peaks, and one envelope is adding a reverb like soft-decaying single-peak envelope.
So the first iteration for a clap-like sound is to have multiple percussive instruments, that are triggered at the same time but which emit, of course, the sound never exactly at the same time, thus imitating the clapping of several people at once.
So I tried out a lot of different combinations of hitting plastic bottles, glass, stone, wood – even shoes – against each other. Finally I decided to go for wood-on-wood, also because I had some piano-mechanics laying around and it all fitted well together.
One thing I noticed when designing robo-mechanic percussive instrument is that you have to have not only an actuator (Solenoid, Motor ..) and that’s it. I use Mass-damper-systems to achieve better results in the beat accuracy. Without the damper, the instrument’s vibration, especially at the slap back, might be too high. This causes the musical instrument to vibrate when slapping back after the beating – and affects the accuracy of the beat when playing multiple beats after another.

So what I usually have is:

+ The mass (beater, stick ..)
+ A spring to hold the beater in the zero-position
+ The solenoid motor, or whatever to apply the force when triggered
+ A damper, e.g. felt, fabric, rubber or another spring

So, the take away robot message here is: use dampers as much as possible to reduce vibration and to keep everything tight. You can never have enough dampers!
What I did not realize is the second envelope part as mentioned above, the slow-releasing reverb-like shape. I did experiment with air pressure, controlled by a pneumatic valve by festo a lot. This can be very great in the future, also for other instruments like the snare, as the releasing air of the compressor makes a sound much like a nice white-noise circuit. With the valve you can control it via Midi. But I didn’t finished it.
The last thing I did stumble upon just a few days ago is this patent by Gary Richard Peterson. He also made a mechanic handclap, which is attachable to a drummers hihat. Sweet!
Here are some pictures of the ready mechanic hand-clap machine driven by solenoids:

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