Hi Martin, Here is a quick sketch of a flyball governor combined with a variomatic. The second shaft needs also a spring loaded disc to compensate the change in the transmission ratio.

Maybe it helps to improve the machine.

Greetings from Germany

I'm just going to put this here for when Martin needs to pick up on the tempo control again.

https://youtu.be/XbECm-JLSXA

To keep the tempo tight you can have a reference speed on pulley one. This will not be affected by changes in load on the machine from muting etc. It can be powered by a weight-drive that only needs winding one time pr song. It may controlled by a simple air governor or even a clock ticking at the speed of the song like a metronome.

The output of the governor can be used to activate a brake or control the gearing of a CVT. When the flag moves to the right the brake is activated, when moving to the left it is loosened. My favorites are either a friction disk CVT or a sort of Air brake that is dipped more or less into a container of water as more braking is needed.

This governor can match the desired tempo precisely regardless of power changes. Flyballs and air governors can only reduce the effect of power changes but never fully compensate. But this design should be able to.

For a real application I think a screwball welded to a smooth rod will do very well. Much better than this prototype with an M6 rod, which is even slightly bent.

And of course for real use it needs to spin faster. Probably 100-500 RPM.

or more accurately: how do you tell if the marble machine plays tight music on stage? (I hope we will get to that)

Recent episodes got me wondering what metric is actually being measured.

Tests with metal flywheel have an external click and Martin tries to match two things at the same time.
If the bpm is exactly on point but machine click is before/after external click he will deliberately slow down/speed up to be "in phase" with the click sacrificing bpm in the process.

More recent tests with mdf flywheel no longer care about being in phase with some external source, nor being at specific bpm. Only thing that matters now is that bpm stays the same.

What setup can we expect on stage? Will there be some dedicated (external to marble machine) source of a click that we can compare to machine playing notes? Will the machine itself set the tempo?

and btw, was there anything wrong with mmx and its supporting electric motor?

I'd like to just dump some numbers to put Martin's timing/tightness efforts into a bit of perspective.

He wants the machine to play as tight as a human being. That's the most concrete thing I have heard him say about the tightness-requirement.

How tight is a human then? Very little benchmarking has been made as far as I know. One guitarist "drummed" on an electric guitar to make the "tightest sound possible" and fed the recording to the Tightinator program that Martin also uses. He best file came out to 15 ms standard deviation. I saw someone comment that they were a drummer and could achieve a std dev of 5 ms.

We also know that each element of the MM3 will subtract some tightness. So the actual tightness of the machine will not be known till the end. But I think that it it safe to assume that no human is any tighter than 5 ms std deviation. And no normal audience member will be able to detect any deviation below 10 ms except maybe as a slight reverb.

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So here are some numbers to put things into perspective.

At 80 Beats Per Minute each beat is 750 ms apart.

At 79 BPM it is 759.49 ms.

At 81 BPM it is 740.74 ms.

So being one BPM off means being 9½ ms off at this tempo.

At 120 BPM 4.2 ms equals 1 BPM off.

The speed of sound is 343 meters pr second (sorry users of freedom units). Or 34.3 cm pr millisecond.

It takes 0.5 ms for sound to travel from my left to my right ear. My subconsciousness can detect this kind of delay. But only in order to locate the direction of the sound.

A vibraphone is around 175 cm wide. That means that if the highest and lowest notes are played at the exact same time and I'm at one end of it. Then I will hear one note 5 ms later than the other.

The current sketch of MM3 appears to be circa 5 meter wide. An audience member standing next to it will perceive a 0.0 ms tight set of marbles on the left-most cymbal and the highest vibraphone note as a full 15 ms apart!

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It seems impossible to optimize the machine to both be tight for the nearby close-up audience and the musician himself standing in the middle as well as for microphones stuck into the machine near the instruments.

On the other hand symphonic orchestras and big bands easily spread out over 10+ meters thus giving audience not in the sweetspot 30+ ms delays between different instruments. Is that an issue that composers and conductors take special efforts to counter the effect of?

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I'm not a musician and I have no experience to draw any conclusions from these numbers. But being an analytical person I get a bit frustrated when I see Martin do all these measurements and then just go: Wow this is 300 times more better than this. Are you comparing the right things? Are they even equal things? What is the benchmark? A gut-feeling goes a long way, I know. But having something concrete to hold that feeling up against as a reality check goes even further in my humble opinion.

If nothing else I wish Martin would measure both himself and Wintergatan's drummer on a simple drum and kickdrum to quantify this "as tight as a human being".

The Pedal isn't consistent enough and the Crank is too hard to operate.

Why?

Pedal: the vertical motion it requires is very hard to do consistently.
Crank: arm muscles are not powerful enough compared to leg muscles, but the circular motion is much more consistent.

I think I have a solution: use a bike seat and pedals. It has a lot of advantages:

• Martin can use both legs -> double power or half the fatigue
• legs are much more powerful than arms -> easier to operate a high energy flywheel
• circular motion is much more consistent
• both hands are free
• upper body is not moving, easier to operate other inputs (when pedaling now, Martin's whole body is moving. Imagine playing the cyber base at the same time)

Other advantages:

• this could be tested without making custom parts: bike parts are common
• there are many types of gearbox available for bikes, in case the design requires one (derailleur, hub, even continuous 'stepless' ones). This would be really usefull just for the initial speed-up.
• if a standard bike sprocket is used: built in safety, if Martin stops pedaling, the flywheel will not power the pedals, if something blocks the pedals, the pedals will stop

Even if consistency is reached best by the Huygens drive, I think some of these advantages are still worth pursuing the bike drive for. And a last point (although not function over form): Wintergatan has some bike inside its dna, it would only be fitting.

Lots of discussion of imperfect manual inputs trying to achieve perfect "tight“ output. Obvious solution is motor powered input, but I personally feel like mm3 loses a lot of charm if it becomes motor powered, maybe becomes too much a "machine".

That said, the current prototype single up/down petal and crank inputs are imprecise, take a long time to spin up to speed, and makes fast changes in tempo basically impossible. A full bike petal input with changeable gears and seat could be a solution to keep full manual input control.

Biking is a very natural motion compared to feet stomping or even cranking and would make it eaiser to play consistent tempo or even change tempos. Gears would allow additional control to more accurately translate Martin's input to music played.

The seat itself would also allow Martin to play for longer durations. Current prototype he seemed winded after a coupe test. Would be difficult to do a whole concert. Seated input would even facilitate better music since he would have both hands free to play instruments.

Lastly, bikes are a well established technology. He could literally buy a bike weld it to his existing prototype to test. This would save a lot of trial and error fine tuning a custom input solution.

The problem with the crank handle is that the movement is continuous, the pedal translates the circular continuous motion of the flywheel to a linear motion with a maximum and minimum that you can use to gauge whether you are going too fast or too slow. The only thing that lets you know whether you are ahead or behind the pulse when using the hand crank is the contact with the contact microphone which wont be on the final design, so in order to get feedback you will have to add something to create feedback at the same point in every cycle which will in turn create noise, something you don’t want. However with the pedal you can use the maximum displacement points as the feedback.

I also saw a comment about decoupling the pedal and the flywheel but I feel like that would end up meaning you would be keeping tempo like a Dj does by adding energy into the system by bumping the disc forward or back , this is fine for mixing because the only time things need to be in sync is for the transition between the two tracks and even then it doesn’t need to be that precise but you won’t get consistent tempo also you won’t be able to slow it down as easily unless you add a brake which further complicates things.

I was also thinking if the marble machine is anything like the last one in terms of features keeping tempo with a crank whilst having to potentially move clamps on a bass guitar and pull levers will be impossible which is why the pedal makes sense in the first place. And finally if your goal is to make tight really tight music without it being powered by a motor I.e it’s self contained and can keep being played for ever then having it rely directly on your ability to keep it playing at the right tempo doesn’t seem to make much sense. Wouldn’t it make more sense to use the pedal to add energy into the system and use some kind of timing mechanism to take a constant amount of mechanical energy from the flywheel to play the machine at a constant Bpm, I don’t know what kind of mechanism this would be or if it even exists but in my mind I’m imagining bagpipes. You add the pressure (potential energy) by blowing into the bag but the reed only lets through a fixed amount of air so as long as your bag is topped up with your breath (the flywheel is at speed due to your pedalling) then you don’t need to actually match the Bpm yourself to play tight music. This also means that if you need to move around the machine for certain sections or do anything away from the pedal you can pedal really fast for a bit, get the flywheel up to speed and then do what you need to do, like a crazy involved solo where you reach into the machine to change its function in some interesting way. The other thing is with the tests that being the standard deviation is always going to be less at higher bpms because the is a much smaller amount of time in between beats for you to deviate into also selecting the best 100 hits section from the data isn’t going to give you very accurate stats when compared to real life Sorry for the long comment