The formula 1 J-damper

[joeqsmith]

There are a lot of papers about it free for viewing.


Compared to the mass damper the inerter is mounted differently within the suspension.

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


https://www.racecar-engineering.com/articles/f1/understanding-the-j-damper/

Even in F1 cars, where comfort is less important, the suspension needs to be set to allow both sensitive handling, which requires a harder suspension, and a good mechanical grip, for which the suspension would normally be softer. The upshot is that there is still some oscillation as the load on the tyres varies, which impedes the vehicle's grip and therefore slows it down.

Professor Smith realised that this poor trade-off between handling, comfort and grip could be better resolved if a third type of component was added to a suspension system to make it more flexible: the inerter.

https://www.cam.ac.uk/research/news/secrets-of-the-inerter-revealed

[nctnico]

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


This is what you'd call mumbo-jumbo.    Sounds more like crystal ball suspension.

[SteveThackery]

If you listen to the professor carefully, you'll hear him mentioning 'impedance matching'. The inerter works like a capacitor so suddenly you can create RLC filters (for example with sharp notches) instead of just RL filters for a suspension system. The video also mentions porpoising (suspension oscillations) which occured in some F1 cars when the J-damper was banned.

Yes, that's the argument made up the thread, but I still can't get it to work in my head.

It is stated that the inerter works like a capacitor. But that seems completely wrong to me. Surely inertia is the mechanical equivalent of inductance. An inductor does to electrical current what the inerter does to mechanical motion. Both resist rapid changes in current/motion, both integrate the emf/mechanical force applied, both have the ability to create a negative-going emf/mechanical force when the positive emf/mechanical force is removed.

So it looks perfectly clear to me that an inerter is the mechanical analogue of an inductor. Obviously I'm completely wrong: the professor says so. So can someone explain how something with mechanical inertia is equivalent to a capacitor?

EDIT: It seems clear to me that the mechanical equivalent of a capacitor is a spring. When an emf/force is applied a flow of current /motion occurs until the emf/force from the charged capacitor/compressed spring equals the driving emf/force. Removing the charging force allows the capacitor to discharge / allows the spring to expand.

[SteveThackery]

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


This is what you'd call mumbo-jumbo. 

Absolutely! It cannot be seen how it will stabilise load variations in that hand-wavey explanation.

[nctnico]

If you listen to the professor carefully, you'll hear him mentioning 'impedance matching'. The inerter works like a capacitor so suddenly you can create RLC filters (for example with sharp notches) instead of just RL filters for a suspension system. The video also mentions porpoising (suspension oscillations) which occured in some F1 cars when the J-damper was banned.

Yes, that's the argument made up the thread, but I still can't get it to work in my head.

It is stated that the inerter works like a capacitor. But that seems completely wrong to me. Surely inertia is the mechanical equivalent of inductance. An inductor does to electrical current what the inerter does to mechanical motion. Both resist rapid changes in current/motion, both integrate the emf/mechanical force applied, both have the ability to create a negative-going emf/mechanical force when the positive emf/mechanical force is removed.

So it looks perfectly clear to me that an inerter is the mechanical analogue of an inductor. Obviously I'm completely wrong: the professor says so. So can someone explain how something with mechanical inertia is equivalent to a capacitor?

Look at the mathematical analogies at 11:46 in the video.

[SteveThackery]

Take a look at this table from a little before 11:46.



Surely velocity and force are the wrong way round? A mechanical force is applied across something - like the two ends of a spring, or the two ends of the inerter. If you apply a force to only one end of something it skitters away across the table.

Intuitively, force must be in the same column as voltage and pressure. They are analogous, are they not?

[langwadt]

https://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html

[coppercone2]

think about it voltage tells you nothing of current so if you say the river has has a 10m/s velocity its like voltage because you don't know if its a stream or the missisipi, you just know that if you throw a bottle in there it should move 10 meters in 1 second

[SteveThackery]

Came across this video, and thought it might be of interest to others.



If I under stand correctly, it is a "two terminal" mechanical device that that produces a force that is opposite to and proportional to an acceleration, so a mechanical analogy to an inductor.

The OP said what I think: the inerter is the analogue of an inductor, not a capacitor, so I'm in good company!

Look at this, from 11:46...



The first row seems wrong. It is normal to say the effect is proportional to the cause. The top left square says exactly that: the current is proportional to the voltage across the resistor. But the top right square is the wrong way round. It should say the relative velocity (the result) is proportional to the force across the damper (the cause).

The second row seems wrong in a different way. The left square says the current is proportional to the integral of the voltage across the inductor, which is correct, but the right square says that the force from a spring is proportional to the degree of compression. Both these statements are correct, but they are not analogous. The right square is pure proportionality; the left hand square involves the integral of the applied force.

I'm not arguing with the proff's claims. But I think there is something very wrong with the explanation from the film maker.

Or more likely I'm too dumb to understand the explanation! 😅

[SteveThackery]

https://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html

Now that's confusing, because the rightmost column is what I'm saying, and the middle column is what the video says!

[Berni]

Yep most things in physics come in such pairs like voltage and current do in electrical.

But the two quantities in the pair are pretty much equivalent, there is no fundamental property that one has over the other. So when you map these between the different worlds of electrical, mechanical, hydraulic..etc there is no right and wrong way around, you can swap what maps to what and it all still works. So we just pick the one that makes more sense in that situation. So for hydraulics it makes sense to map amps and flow rate together since you could imagine the little molecules of liquid running around as being electrons running around a circuit.

In electrical you could swap voltage and current around and measure potential in Amps and flow in Volts. The equations still look the same except that Inductance and Capacitance seam to be doing the opposite thing, but if you swap the equations for those around then it makes sense again (since everything now is on the basis of conductance rather than resistance). Since other systems in physics follow the same kind of equations you can swap those around too as long as you swap everything appropriately.

This is the beautiful thing about physics how the same equations seam to work in all of these systems despite how different they may seam. So if you know circuit analysis and can map a physical system into amps and volts then you can use all the same circuit analysis tricks and it just all magically works.

[hans]

Intuitively, from a point of electrical resistance, I think you're right.

High force / low velocity = high resistance.

But I think their definition is like this because its desirable to have the equivalence of Kirchhoff current law in forces. The net  force (or otherwise current) from a node is simply the summation of all forces (vectors). Doing this for voltages becomes a lot more complicated.

Also velocity is only relative to other bodies or a reference point (much like we use ground). This was also the argument made why a mass is not a pure capacitor: its reference point is supposed to be ground. I think it has to do with how relative velocities would interact with center of gravities, and since inerters have a mass rotating around its own center of gravity, that is perhaps not a problem. But I could be totally mistaken.

These equatable laws may still need some work to translate 3-dimensional (complex) mechanical space into 1-dimensional (complex) electrical space. You can probably replace everything with vectors and matrices, or perhaps work something out with superposition, but things get a bit tricky when dealing with the various divisions that pop up..

[SteveThackery]

think about it voltage tells you nothing of current so if you say the river has has a 10m/s velocity its like voltage because you don't know if its a stream or the missisipi, you just know that if you throw a bottle in there it should move 10 meters in 1 second

But isn't it equally true to say that current tells you nothing of voltage? Both statements are true because they are missing the third element: resistance. When the resistance is known, current tells you everything about voltage, and vice versa.

Or not! 🫤

[johansen]

Which mechanical model works best to model a ram pump as an electrical circuit?

A ram pump works by letting a large amount of water flow down a pipe where a check valve suddenly snaps shut, the pressure spike as a result of the inertia and momentum of the moving water, forces open a valve which bleeds off part of the water and it flows up the pipe.

To me, that's a boost converter. pressure is voltage, flow rate is amps, inertia is inductance.
 
(Initially the flow through the relief valve equals the flow in the pipe minus the energy transferred into the pipe itself expanding with the water pressure, and this loss can be significant, it is effectively an impedance miss match resulting in a reflected wave, which is used to open the valve which allows the water to start flowing again and building up velocity.)


As for an inerter... whats to prevent a F1 team from concealing it inside a shock absorber? One of their Inerter designs was a hydraulic cylinder with a long spiral path for the fluid to flow back into itself, and they filled it with mercury LOL.

How would the rules dictate how long the hydraulic lines on the shock absorbers are allowed to be? you could wrap them around the car to get the dampening and kinetic energy storage you want.

[SteveThackery]

In electrical you could swap voltage and current around and measure potential in Amps and flow in Volts. The equations still look the same except that Inductance and Capacitance seam to be doing the opposite thing, but if you swap the equations for those around then it makes sense again (since everything now is on the basis of conductance rather than resistance).

Thank you, Berni.

I was right - I am too dumb to understand it, because the above paragraph makes no sense at all to me, even though it's bound to be right because Berni wrote it.

Forget about explaining it to me, guys - the problem is with me. I'll take it offline and give it a good thinking about.

[SteveThackery]

Which mechanical model works best to model a ram pump as an electrical circuit?

A ram pump works by letting a large amount of water flow down a pipe where a check valve suddenly snaps shut, the pressure spike as a result of the inertia and momentum of the moving water, forces open a valve which bleeds off part of the water and it flows up the pipe.

To me, that's a boost converter. pressure is voltage, flow rate is amps, inertia is inductance.

Yes! That is exactly as I see it. Inertia is inductance. But the prof (and the middle column of the table shown above) tell me inertia is capacitance. 🤔

[langwadt]

As for an inerter... whats to prevent a F1 team from concealing it inside a shock absorber? One of their Inerter designs was a hydraulic cylinder with a long spiral path for the fluid to flow back into itself, and they filled it with mercury LOL.

How would the rules dictate how long the hydraulic lines on the shock absorbers are allowed to be? you could wrap them around the car to get the dampening and kinetic energy storage you want.

the FIA is not stupid, rules are carefully written and everything is checked, approved, monitored. Breaking the technical regulations is generally disqualification no matter the circumstances

[joeqsmith]

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


This is what you'd call mumbo-jumbo.    Sounds more like crystal ball suspension.

I took that to mean they had modeled some condition, and when that happens the suspension behaves in some known way. 

[nctnico]

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


This is what you'd call mumbo-jumbo.    Sounds more like crystal ball suspension.

I took that to mean they had modeled some condition, and when that happens the suspension behaves in some known way.

Sorry but terms like 'can anticipate the input' and 'cancelled out before they occur' are severe red flags. A system can only respond to input after the input has occured.

[Marco]

You know bumps are generally only a couple cm high. You know how long acceleration will be gone during gear shifts. There's a lot of small time constant events where you can guess how they proceed from the initial suspension force change.

[joeqsmith]

The inerter, however, by operating in harmony with the natural frequencies of the suspension system, can anticipate the input. That way movements and load variations can be cancelled out before they occur. Translate that into the conditions at the contact patch of the tyre and it can be seen how it will stabilise load variations and allow the rubber to generate maximum grip.


This is what you'd call mumbo-jumbo.    Sounds more like crystal ball suspension.

I took that to mean they had modeled some condition, and when that happens the suspension behaves in some known way.

Sorry but terms like 'can anticipate the input' and 'cancelled out before they occur' are severe red flags. A system can only respond to input after the input has occured.

To me, it's just the author trying to convey what is going on to a wider audience. 

Another paper
http://www-control.eng.cam.ac.uk/Homepage/papers/cued_control_860.pdf

[joeqsmith]

You know bumps are generally only a couple cm high. You know how long acceleration will be gone during gear shifts. There's a lot of small time constant events where you can guess how they proceed from the initial suspension force change.

We use techniques like this to speed up some measurements.

[SteveThackery]

I'd like to see a diagram showing exactly how they were utilised in a car suspension. They certainly won't have been a drop-in replacement for traditional dampers.

[joeqsmith]

In a few of the papers I came across, I had seen a couple of photos showing how they were mounted in the F1.  There is a lot of information available.

https://x.com/ScarbsTech/status/1618251526946029568

[joeqsmith]

Onboard camera showing full active suspension compared to traditional.