5 ms·
Is there a 4th missing component in the mechanical world?
- iwr 16y agoWhat's an inerter?
- eru 16y agoSee http://en.wikipedia.org/wiki/Inerter_(mechanical_networks) http://en.wikipedia.org/wiki/Inerter_(mechanical_networks). I am not too happy with that article; does anybody have a better source?
- asmithmd1 16y agoThese notes are pretty "skimmable" http://www-control.eng.cam.ac.uk/~mcs/lecture_j.pdf http://www-control.eng.cam.ac.uk/~mcs/lecture_j.pdf
- pontifier 16y agoMy own experience... I know why this concept sounds so familiar to me. I had one when I was little. There are many childrens toys with a flywheel and a ripcord. That system is an "Inerter"... If the ripcord is a rigid toothed rack and pinion setup then it can act as an "Inerter" in compression as well as tension.
- judegomila 16y agoAn inerter is the mechanical equivalent of a capacitor. http://www.admin.cam.ac.uk/news/dp/2008081906 http://www.admin.cam.ac.uk/news/dp/2008081906
- archgoon 16y agoI question whether the article is correct about the "J-Damper" being a meaningless code-name. In circuit theory, a capacitor can be thought of as a resistor with purely complex (and frequency varying) impedance. Since "J" is the standard symbol for the square root of -1, and given the fact that this device had never been used before, "Imaginary Damper" seems entirely appropriate.
- judegomila 16y agogood point
- davnola 16y agoIt's actually J for "jounce" http://www.f1technical.net/features/10586 http://www.f1technical.net/features/10586
- stretchwithme 16y agoMakes sense to me. Excellent article, thanks.
- kqr2 16y agoAlso see What is the mechanical element equivalent of the memresistor? http://www.quora.com/What-is-the-mechanical-element-equivalent-of-the-mem-resistor?q=mechanical+equi http://www.quora.com/What-is-the-mechanical-element-equivale...
- judegomila 16y agoI sent him an PM. I'm sure there is a lot more to this!
- judegomila 16y agoFrom a friend: "The quantum mechanics stuff sounds very unlikely. Although if you wanted to try and go in that direction you would have to figure out whether circuits have a strong analogy to the Hamiltonian formulation of quantum mechanics (i.e. no discussion of forces!) - then you would be in business. You could then probably formulate a "quantum circuit" in which measurements of voltage and current obey an uncertainty principle"
- judegomila 16y agoAnother interesting question. Given we can move between mechanical and electrical systems with circuit theory. Are their other systems that we could apply circuit theory to (i.e. non electrical and non mechanical systems). Light and space circuits for example?
- Derbasti 16y agoAudio Systems consist of electrical circuits (amplifier, player), mechanical circuits (loudspeaker-membrane) and acoustical circuits (air, room acoustics). All these parts can be modeled as circuits that directly interact with each other. You can actually calculate the electrical properties of the mechano-acoustical loudspeaker+room or the acoustical properties of the electro-mechanical loudspeaker+amp. This is extremely helpful when designing loudspeakers since you can see the electrical, mechanical and acoustical properties all in one notation.
- ticktock 16y agoI once heard an undergrad talk about his crazy professor reproducing digital circuit theory with microwaves running through copper pipes... we were drunk at the time - not sure if there was anything to it, but it sounded plausible.
- AlexandrB 16y agoA classic one is heat transfer: http://en.wikipedia.org/wiki/Lumped_capacitance_model http://en.wikipedia.org/wiki/Lumped_capacitance_model You can also model some hydraulic systems using components analogous to electronics (flow=current, pressure=voltage, pipes=resistance). For example a certain pressure applied to a pipe of given size (cross-section + length) and material will result in a predictable rate of flow.
- kwantam 16y agoBasically any LTI differential equation can be modeled as a network of Rs, Ls, and Cs. You can get fancier if you want by adding nonlinear elements. In other words, anything you can describe as a differential equation has an analogous circuit. In fact, I've read the claim (though I cannot, for the moment, find the reference) that the term analog was first applied to circuits which were being built to solve LTI differential equations: the circuit was the analogue of the equation, thus it was an analogue (eventually, just analog) circuit.
- secretasiandan 16y agoCharge being equivalent to position doesn't make much sense to me. When I learned systems modelling, we studied spring-mass-damper systems right next to electrical circuits and I have ever since thought of a capacitor as equivalent to potential energy, an inductor as equivalent to inertia and a resistor as equivalent to friction.
- moron4hire 16y agoNo, charge would be equivalent to potential energy, resistance would be equivalent to friction, etc. You're confusing a property and objects that effect that property.
- colanderman 16y agoThat's a common view, since force ~ voltage, current ~ velocity (i.e. charge ~ position) seems "intuitively" correct, but it breaks down when you look at what would be the equivalents of KVL and KCL. KCL states that currents sum to zero at a node in the absence of capacitance: this is similarly true of forces (capacitance in this case representing the ability of the node to change position/"charge"). KVL states that voltage differences sum to zero around a loop: this is similarly true of velocity differences. This can be difficult to visualize, but imagine a loop of N springs. Assume the loop can have no net translational motion (as above, this means it is not capacitive). Now imagine the different ways each spring can move individually. The loop could rotate as a whole, meaning half the springs have are moving "up" (i.e. have a positive voltage across them) and the other half "down" (i.e. have a negative voltage across them). The loop could be still, but for one element compressing and its neighbor expanding (i.e. all zero voltages with one positive and one negative). The reason the examples in your systems class worked was likely because the circuits were simple enough that their duals shared the same, or similar, network structure. You can see this with a purely electrical circuit -- analyze a simple LCR loop, and then swap the L & C equations and you should get the same result. This breaks down for larger circuits, where you must find the dual network in addition to swapping Ls and Cs.
- secretasiandan 16y agoThe invetor's slides say that the only time the analogy breaks down is with ungrounded capacitors, though its unclear to me what exactly that means (I don't really feel like thinking too hard about it). See slide 17 http://www-control.eng.cam.ac.uk/~mcs/lecture_j.pdf http://www-control.eng.cam.ac.uk/~mcs/lecture_j.pdf There are actually a few different analogies you can make between electrical/mechanical devices. See the top table "Key Concept: Analogous Quantities". This is part of the reason why I don't feel like thinking too hard about what the inventor means when he says the analogy "breaks down" with ungrounded capacitors. http://www.swarthmore.edu/NatSci/echeeve1/Ref/LPSA/Analogs/ElectricalMechanicalAnalogs.html http://www.swarthmore.edu/NatSci/echeeve1/Ref/LPSA/Analogs/E... The inventor has created a "new analogy" where the inerter is a capacitor. I read your post as saying the old analogies don't work. Is that correct?
- moron4hire 16y agoWhy isn't an inerter just a flywheel?
- colanderman 16y agoBecause flywheels have only one usable node; the other is effectively "grounded". They're also rotational; if you're working with translational systems (e.g. suspensions), you need something else. An inerter, being basically a flywheel connected to a rack gear, meets both these requirements. You have two nodes (the flywheel's axis, and the rack gear) and the motion is translational.
- moron4hire 16y agothanks
- colanderman 16y agoAdditionally: a rotational inerter can be made by connecting the ring gear of a differential to a flywheel. The two nodes are then the two side gears of the differential.
- gfodor 16y agoIt's "memristor", not "memresistor"
- foobar2k 16y agoactually, both are acceptable terms
- kwantam 16y agoI've never been convinced that the memristor is worthwhile to consider as a "fundamental passive device" as everyone seems to want to claim. There are a few reasons for this: (1) It's underspecified compared to the fundamental passive circuit elements. For linear R, L, and C, each has one parameter, its value. Ignoring trivial cases (viz., resistors), a memristor has as its memristance an arbitrary function of V and I. As a result, any interesting memristor is automatically not LTI. (2) It's not particularly special. Why don't we also define a memcaptor, whose capacitance is a function of its current history? I could easily do this, for example, by making a capacitor where one plate is attached by a spring to a fixed support; then, by adding charge, I move the plate and increase the capacitance (or, by removing, I decrease it). Oh wait, that's just a nonlinear capacitor. In the same way, the memristor is just a funny name for a particular kind of nonlinear resistor. (3) It's not particularly practical (for the moment). It can't be made in anything but a very specialized, presumably extremely expensive process. I hope this changes---I'm sure it'll encourage someone to use them!---but at the moment this really limits my excitement. (4) There's nothing I can build with a memristor that I couldn't build already. This isn't like the invention of the vacuum tube: you give me a memristance function, and I can build you a pseudo-memristor out of transistors, Rs, Ls, and Cs. Yes, it could be less {space,power,?} efficient, but this is not a quantum leap in technology the way the vacuum tube was (one could not, with 1890s technology, reasonably build something that emulates a vacuum tube). I'll admit that strictly interpreting my last argument, the vacuum tube could be made to emulate a transistor and thus the transistor wouldn't count as a quantum leap---clearly ridiculous. However, I'd contend that the real value of the transistor was only evident once it was sufficiently miniaturized and its production was sufficiently cheap. You show me memristors that are six orders of magnitude cheaper than transistors and by golly I'll be a convert. Even then, it'll just be yet another nonlinear device with which we can do interesting things---and just like the transistor, the memristor will simply never be as fundamental as R, L, or C.
- judegomila 16y agomemcapacitor and meminductors have been proposed in 2009. You can build the memresistors out of combinations of components but it doesn't allow for miniaturization and low power usage. I.e. the application in RAM is going to be huge!
- judegomila 16y agoFrom Prof. Malcolm Smith "I have always thought that the memristor is rather a weak concept. It is defined as a device with a nonlinear relationship between flux and charge. A linear memristor is the same as a resistor, so in linear circuits the element is not meaningful. The definition does not pin down the type of nonlinearity. So the difference between a variable resistor and a memristor is not sharply defined. The mechanical equivalent of a variable resistor is of course a variable damper. Variable dampers and semi-active dampers are of course used a lot in suspension systems"