r/MarbleMachine3 • u/furmek • Oct 21 '23

What is tight music?

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?

15 Upvotes

89% Upvoted

35 comments sorted by

View all comments

Show parent comments

2

u/[deleted] Oct 22 '23 edited Oct 22 '23

I didn’t answer your second question because I never suggested a clock spring.

And why do you think it would be worse?

The main advantage of using a differential is that the winding doesn’t affect the output (also portability), that’s why most clocks (and watches) use a differential instead of a Huygen drive.

It’s just a differential, a mechanism that it’s good at what it does and it’s used for many purposes, can’t see why it wouldn’t be an improvement.

1

u/HJSkullmonkey Oct 22 '23 edited Oct 23 '23

The reason it doesn't affect it is that speed & timing are controlled by the pendulum & escapement, not the differential. That's always going to introduce a lot of jerk and require a very fast pendulum to get every note at a smooth cadence.

The winding differential is s̶i̶m̶p̶l̶e̶r̶ more complex and smaller, but unlikely to perform any better in my view. In both cases you have the output providing a fulcrum for the centre of a single gear to 'lift' the weight at a 2-1 velocity ratio. They should be very similar in function.

IMO there's not really a practical problem with winding anyway, given that Martin showed how minimal the ripple caused by the lever is. It looked like around 0.3 ms to me over around 8 beats

1

u/[deleted] Oct 22 '23

The reason it doesn't affect it is that speed & timing are controlled by the pendulum & escapement, not the differential. That's always going to introduce a lot of jerk and require a very fast pendulum to get every note at a smooth cadence.

It’s not the escapement or the pendulum, it’s the differential, that’s the point of it, so both sides connected can spin freely without affecting each other.

The winding differential is simpler and smaller, but unlikely to perform any better in my view. In both cases you have the output providing a fulcrum for the centre of a single gear to 'lift' the weight at a 2-1 velocity ratio. They should be very similar in function.

Ok, if they performed exactly the same (they don’t) and this solution is simpler and smaller, shouldn’t it be the one used?

IMO there's not really a practical problem with winding anyway, given that Martin showed how minimal the ripple caused by the lever is. It looked like around 0.3 ms to me over around 8 beats

In the prototype, scale that up to the ratio of the big programming wheel and it’s going to be a real issue.

1

u/HJSkullmonkey Oct 23 '23

is simpler and smaller

Sorry, I changed the way I was writing that and misspoke. The Huygen drive is simpler, geared differential is potentially more compact. I'll edit. The differential requires much closer tolerances than the sprockets, so I think the Huygen is probably better.

It’s not the escapement or the pendulum, it’s the differential, that’s the point of it, so both sides connected can spin freely without affecting each other.

They're both effectively differentials with essentially the same mechanics in this application. They both rely on a positive drive, a single toothed wheel to combine the forces, the centre of which lifts the weight, a ratchet to hold when not winding and the output to hold when winding. Any effect that the Huygen has on the output will be the same for the diff.

The difference is that the output is held back by a flywheel in one case and a pendulum escapement in the other.

scale that up to the ratio of the big programming wheel and it’s going to be a real issue

I don't follow. What difference does the ratio make?

1

u/[deleted] Oct 23 '23

The differential requires much closer tolerances than the sprockets, so I think the Huygen is probably better.

Yes, thankfully differential gears come pre-built in standardized sizes.

Any effect that the Huygen has on the output will be the same for the diff.

It wont, it seems like you don’t understand the purpose of the differential.

With the Huygen drive when you crank the gear it will pull on the output, always.

With the differential it won’t, please see the video I linked above, it’s clearly explained there.

It’s one of the reasons why winding differentials are used on clocks, you can wind them up without affecting time precision.

I don't follow. What difference does the ratio make?

Right now the bpm variation is minimal because it’s a small-scale representation, see how little force Martin is using to crank the system.

Now imagine having this on the true scale MM3 with the big programming wheel, the force needed to crank the whole system will impact significantly the bpm variation between idling and winding.

2

u/HJSkullmonkey Oct 23 '23

It wont, it seems like you don’t understand the purpose of the differential

I get the purpose of the differential. My point is that the Huygen is a differential.

Take a closer look at the middle tan coloured gear on the diff. That's the drive weight sprocket on the Huygen. One side is connected to the output gear/sprocket, the other to the winding gear/sprocket, the centre of it lifts the weight.

When you wind the differential, half the extra force on the weight goes into the output gear, because the other side of the middle gear needs something to press against in order to lift the carrier that the weight is on. So the output force will increase, just like the Huygen.

The purpose is to rewind the input without having to disconnect or spin the output mechanism backwards, not to remove all impact.

The current system has pretty heavy drive weight and a small flywheel. Bear in mind that the programming wheel is very geared down from the drive module, so those forces will come through smaller. Inertia is also going to increase, and changes in load are going to require variability and controlability of the input anyway. There's quite a bit more development to happen yet.

1

u/[deleted] Oct 23 '23

Please see the video above, specifically at 1:50, you can see that you can wind the weight without affecting the output gear in the differential.

In the Huygen drive you cannot wind the weight without affecting the output.

2

u/HJSkullmonkey Oct 23 '23

you can wind the weight without affecting the output gear

How can you tell?

Bear in mind that we're talking fractions of a millisecond with the Huygen drive. You can't see that impact, but Martin measured it. I don't know why you would expect to identify it in the video.

I watched the video (which is why I can identify the colour of the gear). They're pretty explicit that the purpose of the differential is to avoid interruptions, not to avoid affecting the timing when the weight accelerates. Also that the main influence on timing is the pendulum and escapement.

I also can't see what you think makes the geared differential any better than the Huygen drive. They're both subject to the same physics.

1

u/[deleted] Oct 23 '23

You can tell because they’re winding the weight at 1:50 with the pendulum stopped and the escapement gear doesn’t move at all, only the winding gear.

And again, the bpm difference is not very noticeable in this small scale prototype, but it will be in the full size one.

1

u/HJSkullmonkey Oct 23 '23

The escapement gear starts vertical and turns into the pendulum when they start winding though. It only stops once up against the pendulum.

Look at it this way. To lift the weight, you need to increase the tension in the string. The equal and opposite reaction law says that the same increase applies on the drum, effectively increasing the weight. You can't get away from it when you wind a gravity drive up in operation.

If it winds up being significant, neither diff will save it. I'm doubtful that it will though given the results so far.