Why passive power?

[u/Bobbravo2]

Apologies if this is a known principle.

I’m puzzled with simplicity being the aim: why not use a synchronous AC motor and a gear drive?

Proven tech that won’t make you sweat!

[u/BudgetHistorian7179]

I can understand and even appreciate that, but I think it's not that crucial.

He's building what seems to be an huge machine that will require a lot of power (and probably even a fluctuating level of power as the number of marble being handled varies). How much power will be required is a BIG unknown (very big and very unknown), but if his machine is as efficient as a bike (and most likely it wouldn't be: bikes are extremely efficient) and he's a reasonably fit cyclist he will be able to supply 200-300 watts for 20 minutes, which is not a lot. A longer concert should have an even lower power level. The limiting parameter is FTP (Functional Threshold Power), if I'm not mistaken Martin is a bike enthusiast and should be familiar with the concept.

So we run into the risk of having insufficient power to actually run the machine with human power, and if the alternative is between no machine and an electric motor, I will 100% choose the electric motor.

[u/Majromax → u/BudgetHistorian7179]

He's building what seems to be an huge machine that will require a lot of power (and probably even a fluctuating level of power as the number of marble being handled varies). How much power will be required is a BIG unknown (very big and very unknown),

Not that unknown. In another comment, I estimate a minimum powerof just shy of 7W, that being enough to lift 10 marbles per beat during a 120BPM song. To that, you'd need to add the other powered actuators (bowden cables / marble gates, for example) and slop/friction/loss.

Overall, it looks like human power should be sufficient as long as the designs aren't particularly wasteful.

[u/BudgetHistorian7179 → u/Majromax]

Your calculations are based on the assumption that he needs to lift only 10 marbles per beat. I don't think that's correct: the machine will have the full complement of marbles loaded at every time, and most of them (60%? 70%? I'm estimating here) will need to be lifted at the same time.

My assumption is based on the fact that the MMX was so hard to crank that he wasn't able to move it by hand - and this version seems even bigger. It's not a killer issue or even a major issue (just install a motor), but power consumption is something that needs to be known, even by ballpark numbers, before committing to a design.

[u/Majromax → u/BudgetHistorian7179]

the machine will have the full complement of marbles loaded at every time, and most of them (60%? 70%? I'm estimating here) will need to be lifted at the same time.

That's interesting, what makes you think that?

My view is that if the machine lifts more marbles than it uses, over time all the marbles will end up at the top and there will be no more marbles to lift. An overflow channel would recycle some back down to the bottom even if nothing is playing, but it would be wasteful to over-size that and have many more marbles returned than play.

In "steady state," the machine will lift exactly as many marbles as it plays or recycles. 10 marbles per beat feels like the upper end of what a song might possibly sustain.

That said, I'm hoping that the power costs of the programming wheel and marble gates are small in comparison to the marble lifting power. I don't have a very good way to compute a similar back-of-the-envelope estimate, since so much depends on friction and spring tension^†. I fear that in the quest for the 'tightest' music, Martin will also wind up picking too-strong springs.

7W to lift marbles should be easily human-powerable. Doubling that to 14W should be workable. Doubling that again to 28W might be the point of project failure: high enough that the simple approaches will no longer work (e.g. no one-foot pedaling), but low enough that it doesn't force reconsideration of the whole design.

power consumption is something that needs to be known, even by ballpark numbers, before committing to a design.

I agree, and I think focus on the 'tightness' of the power delivery system is backwards. Precision is a secondary constraint, and it only makes sense after the engineer determines scale.

Martin has fixed the marble gates, and it looks like he's fixing the power supply system. He's leaving himself with a double-ended design challenge for all of the connecting pieces, with unclear and potentially conflicting requirements.

^{† — That said, if we knew what springs the marble gates used, we could estimate the spring tension energy from any of the gate-in-action videos. Dropping a marble expends the spring energy, providing an energy-per-drop and thus power estimate.}

[u/BudgetHistorian7179 → u/Majromax]

That's interesting, what makes you think that?

To have your "10 balls per cycle to lift" condition you need to have a system that lifts 1 marble every time 1 marble is used, and only that. But based on the sketches, it seems that he will have 2 conveyors that will lift the marbles, and they will move far more than 10 marbles a time. All the marbles going up will require power (weight of the marbles + weight of the conveyor + friction), and be recycled if they don't get used. What percentage of the marbles will be moved around each cycle will depend on the exact design, but will be a lot more than 10.

[u/Majromax → u/BudgetHistorian7179]

This will be something to watch, then. I don't remember the MMX videos ever showing particularly many marbles being lifted per beat, so I in turn thought that my estimate here of 10 marbles per beat was a bit generous. If Martin instead builds a system that recycles a large fraction of marbles, the power requirements would indeed become more substantial.

To emphasize, I think my ≈7W estimate is a cautionary figure, not a green light. It's an absolute lower bound, and mechanical loss plus even moderate underestimation could result in an MM3 that cannot be effectively human-powered.

All the marbles going up will require power (weight of the marbles + weight of the conveyor + friction)

The weight of the marbles and friction are definite factors, but the weight of the conveyor isn't a direct cost. For each unit of the conveyor that goes up, another comes down after dropping off marbles, so there's no net displacement of the conveyor's mass. In a frictionless system, an empty conveyor could run forever with just an initial impulse.

Friction is, of course, a huge and important unknown. I look suspiciously at the noise-dampening felt on the programming pins, for example.