Lovey-Dovey - 06 November 2009 11:41 AM

I was an uncle. Now I'm an auntie. My nieces and nephews are very confused.

auntysquat - 06 November 2009 07:49 PM

I guess I deserved that. Stupid karma, golden rule bull.....

Lovey-Dovey - 06 November 2009 07:55 PM

Meh ... I can take it and dish it out.

auntysquat - 06 November 2009 11:15 PM

You don't know 'Squat.

Lovey-Dovey - 07 November 2009 12:45 AM

The secret to mechanical grip is to reduce rapid load variations at the tyre contact patch. This simple truth has been known for years and is the objective of tuning suspension dampers. To this end, teams all over the world run thousands of hours of expensive rig testing time in order to better understand this. More recently, mass dampers have been employed to achieve the same aim, most notably by Renault F1. But it also emerged that the McLaren team had pre-empted their use with its subtle and complex inerter.
The concept for the inerter originates in Cambridge University and Malcolm C Smith’s work on electrical and mechanical systems. There has been a long-standing observation that most elements in an electrical circuit have a mechanical equivalent. By viewing a mechanical system as an equivalent of an electrical one, a different perspective can be taken on how it works and how the elements interact with each other.

There are different views as to how this equivalence should be defined, but for his work Smith has adopted the convention that force is the mechanical equivalent of current and velocity equates to voltage. Likewise, certain electrical components have mechanical counterparts. He equates the mechanical spring to the electrical inductor, the damper to a resistor and a fixed mechanical point to the electrical ground of a circuit, though he notes that up until now, within his preferred convention, there has been no obvious direct mechanical counterpart to the electrical capacitor. However, the mass of a body can be equated to a capacitor under a special set of conditions. That is, it has inertia, but that inertia is relevant to its position in space. In that sense it is like a grounded capacitor whose potential is relative to earth. What did not seem to exist was a mechanical element that could be used like a capacitor in isolation. In other words, with two terminals and the behaviour of which was dependant on the load across those two terminals and not its movement relative to its position in space.
Without this element, it would not be possible to replicate most electrical configurations mechanically.
It was while considering this that Smith came up with the idea of storing kinetic energy rotationally in flywheels. They could capture and release large amounts of mechanical energy, while having an insignificantly small inertia relative to their position. By gearing up the flywheels to increase their speed, a greater amount of energy can be captured without increasing the mass of the device and its inertia in space.
As an attempt to create this effect, Smith started with a configuration as in Figure 1. One terminal is mounted on the casing that houses the gears. The other is on the end of a rack that spins a gear that, in turn, spins a flywheel at high speed.

To consider how much energy is stored, we can derive a simple formula. If we define the following:

r1 = radius of the rack pinion
γ = radius of gyration of the flywheel
r2 = radius of the gearwheel
m = mass of the flywheel
r3 = radius of the flywheel pinion

Also the velocity of the rack is the velocity of one terminal minus the velocity of the other or:

v = v2 – v1

Then:
α1 = γ/r3

α2 = r2/r1

To show how effective this concept can be, if one was to set both α1 and α2 at 3.0, then the inertance factor will be 81 times the mass of the flywheel. From this it is easy to see how the actual inertia of the unit due to movement of its centre of gravity is relatively insignificant compared to the energy that can be captured and released by the device. In fact, one of Smith’s first prototypes had an inertance-to-mass ratio of about 300.
In order to use the inerter to successfully damp cyclical behaviour in a car’s suspension it is necessary to tune the device to the frequencies likely to be encountered in the system. In Smith’s words, ‘We define the ideal inerter to be a mechanical, one-port device such that the equal and opposite force applied at the nodes is proportional to the relative acceleration between the nodes.’

The constant b is the inertance measured in kg and equates to McLaren’s zogs. This was all part of the team’s efforts to keep its new technology secret. Firstly, the team christened its inerter a J-damper, or jounce damper, as was revealed in the secrets to Renault case last year. Then, rather than using the term inertance, which would have been a big giveaway in the pits if anyone overheard it, the engineers came up with the term zog. In pit garage parlance, ‘can you change to a 50-zog J-damper.’ The actual relationship between zogs and kg is still only known within the key people at Woking.
Getting this relationship right, however, is critical, not only to making the J-damper work effectively, but also to avoid huge loads should the damper and the suspension start cycling together. In the worst case it could rip the damper and even the suspension apart. Indeed, some believe this was the cause of Fillipe Massa’s suspension failure at Monza last year, as Ferrari struggled to come to terms with the new technology.

Much like a conventional suspension damper, the ideal inerter for a suspension system can be approximated by calculation.
Compared to the mass damper the inerter is mounted differently within the suspension.

In figure 2, the mass damper (m) is attached to the sprung mass (M) and uses its inertia relative to its position in space to exert an opposing force on the main mass to calm its motion. In contrast, the inerter in figure 3 between the mass and the exciting force can absorb and return mechanical energy in harmony with .................

Oh, I'm so tired of reading about mass dampers and inerters .... I think I'll go to bed now. 'night, Mrs. Dovey.

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auntysquat - 07 November 2009 01:08 AM

^ Gives my head ow-ees.

Lovey-Dovey - 07 November 2009 04:40 PM

I'll write you a prescription for smart pills. Take two before bed and call me in the morning.

auntysquat - 08 November 2009 02:07 PM

Jeremy Mayfield and JC France are a couple of my customers.

Lovey-Dovey - 08 November 2009 07:41 PM

I kidnapped Lisa Mayfield's cat.

auntysquat - 08 November 2009 11:05 PM

I'm the next Mr. Lisa Mayfield.