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New inertia drive

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New inertia drive

Postby nix » Sun Mar 01, 2020 9:36 pm

Heya,
I have been out in my shed recently,
and have found a really simple build that is a contender for a drive in space->
https://www.youtube.com/watch?v=YUDggX5NfwU
It utilizes inertia and relative mass

Do you think it would work in space?

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Re: New inertia drive

Postby trogluddite » Mon Mar 02, 2020 1:32 am

nix wrote:Do you think it would work in space?

In short - No; and if it did, spacecraft designers would almost certainly already be doing it, and astronauts on space-walks would be able move themselves around with comical variations of my incredibly funky dancing (I may have got "comical" and "funky" the wrong way around there!)

In the first example, displacement is produced primarily because static friction ("stiction") is stronger than sliding friction. Ignoring inefficiencies of the pneumatics, energy lost to sound and heat, etc...

If the same amount of energy is going into the piston in each direction, moving it over a shorter time period creates greater force at the sliding surface (force = mass * acceleration), so stiction is easily overcome, and the "vehicle" part is then able to slide over the worktop as the lesser frictional reaction force is insufficient to oppose it, and the two parts separate from the barely moving centre of mass of the composite object.

Doing it over a longer time period creates insufficent force to overcome stiction between worktop and "vehicle", so the same energy is put into moving the "inertial mass" (and centre of mass of the composite object) by a larger distance. The analysis of rolling resistance is somewhat more complex than sliding friction, but is analogous enough in practice that the example with the bearings is essentially the same in principle.

Floating freely in the vacuum of space, there are none of the surface or rolling contacts necessary to create these conditions; so there would be no net acceleration of the centre of mass, just a redistribution of mass around that centre - the two piston movements would exactly cancel out regardless of the speed of movement, and the result would be the same as if you never actuated it. To make the vehicle accelerate and then keep moving in a vacuum, the mass moving in the other direction has to separate from the vehicle, because so long as they don't interact with anything else, the problem can always be reduced to a single rigid object with the same mass and centre of mass as the composite object. Even if they separate, the system as a whole is equivalent to them being joined with a massless piston rod that can be extended forever.

There is no way to do it without effectively requiring the vehicle to lose mass (e.g. the products of the burned fuel ejected from a rocket engine), at least, not without harnessing gravitational acceleration or some other external influence.

Sorry to be a party pooper! But kudos for your inventiveness - and I'm incredibly jealous of your shed!
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Re: New inertia drive

Postby nix » Mon Mar 02, 2020 6:41 pm

Hey thanks Troggie!
I'm happy that I have made a curious earthly motor
So I can't hang this from a pendulum either of course(as it's a frictive point)?
-or put it floating on water?
I'm still trying to understand this entirely!
The concept of an everlong piston is so strange
ta for liking my blunt instrument approach
I wish u could use my workshop-
it's a great sketchpad
I am using pickups for tachometers in our shared technical/audio concerns
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Re: New inertia drive

Postby trogluddite » Mon Mar 02, 2020 8:07 pm

The pendulum example is an interesting one. If you change the centre of mass in harmony with the period of the pendulum, you could very easily make it swing wider and wider. That's exactly what we do when we're on a playground swing by leaning and sticking our legs in and out (I often wish that playing on the swings as a grown-up with no kids didn't elicit such dodgy suspicions from other people - I really enjoy it!)

And in principle it could be made to work in air or water too, because fluid drag scales approximately with the square of velocity (so long as you're nowhere near the speed of sound!) - so you could still generate that difference in "friction" between slow and fast motions of the piston. However, something very lightweight designed to "catch" the fluid (i.e. a sail or oar) would be a lot more effective - the difference would most likely be far too small using a dense mass to overcome the losses in other places.

I'm a big fan of "amateur" inventions; it's a kind of creativity that's very underrated, IMHO. I also really like what the Japanese call Chindogu - where silliness and impracticality are all part of the fun, like the mad machines of Heath Robinson and Rube Goldberg. I've often wished that I lived a couple of hundred years ago, when huge leaps in science and engineering were still regularly made by people tinkering in their home workshops; and I think it's great that people continue the tradition, whether seriously or just for laughs (I'd probably have more likely ended up as a workhouse pauper back in those days, though!)

FWIW, I've long harboured the ambition to build myself a "Strandbeest"!
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Re: New inertia drive

Postby deraudrl » Tue Mar 03, 2020 1:24 am

trogluddite wrote:I also really like what the Japanese call Chindogu - where silliness and impracticality are all part of the fun, like the mad machines of Heath Robinson and Rube Goldberg.
Well then, I give you this:
https://www.youtube.com/watch?v=C_CDLBTJD4M
An organic gravity-powered synthesizer/sequencer.
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Re: New inertia drive

Postby trogluddite » Tue Mar 03, 2020 2:30 pm

deraudrl wrote:An organic gravity-powered synthesizer/sequencer.

Cheers! There's something about the simplicity of it (not to mention the patience required to set it up) that I really like. Unlike this one that did the rounds a while back (and requires rather more physical effort to add a bit gravitational potential energy)...
Wintergatan
(I couldn't resist it for its inclusion of a bit of Lego!)
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Re: New inertia drive

Postby tulamide » Thu Mar 05, 2020 8:59 pm

To make the vehicle accelerate and then keep moving in a vacuum, the mass moving in the other direction has to separate from the vehicle

And that's the only form of so called mass drivers that work in space. There are quite a lot of concepts, NASA, ESA and others are working on. Most involve superconducters, an electromagnetic field and any kind of mass that's propelled by it. A nuclear reactor could provide the energy needed and the mass itself doesn't need to be "heavy" (in earth terms), because it will add up over time.

A conventional car engine works by repeatingly exploding an air-fuel mix, and that's the same principle concept.
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