Quote from ajp71 :

For my A2 DT project I'm designing and building a rolling road for a small electric car. It needs to be able to produce resistance approximately like the car will experience in a racing environment and allow long high load tests. The common method used in car rolling roads seems to be a water based resistance system, which sounds rather complicated or rarely an electric motor based system, which sounds more complicated.

From what I can remember the water system is a simple friction brake with water cooling of the braking parts. I did an experiment at university with an old (1904, I think!) single-cylinder gas engine attached to such a dyno...if you know the water flow rate and the temperature rise of the water flowing through the braking system you can calculate the power being dissipated

I'll have a look through some books at work tomorrow...our rolling road is a fully transient AC electric system but we've got some old textbooks in our 'library' which describe some other dyno systems.

I'm not an expert in dyno hardware but I would imagine that any sort of electric motor would be able to absorb power from your rolling road. Connecting a high-power, low value resistor across the motor terminals should build up quite a lot of resistance when the motor shaft is turned. Add in a voltmeter and current meter and you should be able to calculate the power being absorbed. Don't quote me on that though

Quote from Mako. :

I just dont see how REMOVING a speedometer completely is a good idea. Even on the track, you need it. You need it to gauge how fast you're going into a corner, how quicly you gain/scrub off your speed, pit lane for no limiter cars (btw, the limiter only works once you get realy close to 50mph, so if you fly in and press it right before the enter line going 100mph, it's not going to help ya.

How can you drive withought one? Confuses the f8ck out of meh.

You're supposed to be going as fast as the car will go! Part of the skill of driving is feeling where the limit is and not exceeding it. It doesn't make any difference what speed you're going as long as long as you're at the limit.

Maybe I just trained myself not to look at the speedo during my GPL days

Wow...lots has happened in 24 hours! Been busy at work, then went to do some PC repair for a friend so no time for posting

Anyway, it seems like the issue has been more or less sorted. Going back to my diagram (end of page 1), obviously the analysis only applies if the damper rod has reached its full extension and the elastic modulus of the rod can be considered as a part of the system. It's true that in that specific case, you'd have to add a force equal to the preload force to get the damper off its end stop and get the spring moving. However, once it's moving, the spring rate is exactly equal to the spring rate of the spring, with or without preload.

Obviously when the suspension is fitted in a car you'd hope never to reach the end stops of the damper (in droop or bump), so this analysis isn't representing the correct situation. However, if you imagine hanging the car in the air with the suspension at full droop, then lowering it gently, I think my equations work. Once the damper is clear of the end stop, however, I think the preload only acts to reduce the ride height by the preload distance (multiplied by the bellcrank ratio).

Quote from tristancliffe :

With one inch preload the car already takes up the preload statically (and more so with downforce and cornering load transfer). In other words because the preload is already overcome just supporting the car (even if we use lots of preload) I don't think that's an issue. But there would be a slight reduction in wheel rate - i.e. the car is effectively slightly softer sprung. I'd need to do some maths to work out how much it varies, but I'd be shocked if it was lots.

I'm not sure I agree on the 'slight reduction in wheel rate'...the preload only seems to affect the offset, rather than the slope, of the load/displacement line. So, assuming no change in the bellcrank position, where does the reduction in wheel rate come from?

Quote from Shotglass :

because the damper at full extension is essentially a metal rod

OK, I think we're getting somewhere. I've attached a quick sketch of the system as I understand it.

Fp is the preload force and xp is the preload compression of the spring (k1). k2 is the spring constant of the metal bar of the damper and x2 is the extension of the damper rod. The extension of spring k1 is (xp-x2). We can apply a force F to the end of the damper rod, which is rigidly attached to the spring k1. Let's assume that the system is in equilibrium, i.e. we have added a preload and it is now sitting on a table. The forces at the end of the damper rod must balance.

F + (k2 * x2) = k1 * x1

but x1 = xp - x2, so:

F + (k2 * x2) = k1 * (xp - x2)

Which leads to:

F = (k1 * xp) - x2 * (k1 + k2)

Since the system is in equilibrium, the force F is zero and the preload force in k1 is exactly balanced by the extension of the damper rod k2.
Thinking about this equation, the spring constant of the whole system at this point is zero. That is, any small force F will cause the system to move. The spring constant then increases as F increases until x2 = 0, at which point the damper begins to move and k2 disappears. We're left with:

F = k1 * xp - (x2 * k1)

which, since x2 = 0 at this point, reduces to

F = k1 * xp

which is Shotglass' 'biasing' preload force. However, as x2 becomes negative, the spring rate of the system returns to k1 and the preload simply becomes a 'force offset'. What's the effect of this force offset? It raises the ride height


On reflection it seems that I had misunderstood Shotglass' point. He is, of course, right about the 'biasing' thing but this doesn't affect the spring rate of the system, only the equilibrium point.

Now I leave it to you fine people to ridicule my force diagram

Quote from Shotglass :

GAH again

preload doesnt add weight ... its a weightless force on the spring...

How does the spring 'know' whether the force is weight or preload? The spring simply changes its length according to the applied forces, whether they're weight or preload.

Quote :

...which is used to deform the damper and its casing in an elastic manner (the damper being a streched spring of its own)
you then have to push the damper back into its original form before you are able to compress the spring

I don't understand. How does the damper act as a spring?

Quote from Shotglass :

GAH
that force is still in the system currently trying to lengthen the damper (which it cant) and you first have to equalize that to change the springs length to any degree

forces dont just fade away into thin air

Let's say we have a spring which is 20 cm long and has a spring rate of 50 N/cm. It is sitting on a hard, flat surface. We also have 2 weights, each weighing 100 N (10 kg). Now, you'd agree that by Hooke's Law, placing all three weights on the top of the spring should compress it by (2*100)/50 = 4 cm, leaving the spring 16 cm long?

Let's add the weights one at a time. Weight number one will compress the spring by 100/50 = 2 cm.
Now let's add the second weight. By your logic, the spring shouldn't move, since there must be an extra 100 N of 'preload' in the spring because of the first weight. The extra 100 N weight will simply balance this 'preload' and the spring won't change in length.

But we agreed before that the spring should only be 16 cm long...

Quote from Shotglass :

I think what we can easily agree on is that a spring works according to Hooke´s law which is:

F = k*x

For simplicity´s sake we assume that the spring is fully extended when the damper is fully extended, ie. the springs length matches that of the damper or in other words the spring wont kill you if the gear used to put it into the damper fails since you dont need any.

So if we were to compress the damper, discounting that it dampens, the force needed to compess the spring by x directly follows from Hooke´s with x=0 being a fully extended damper.

If you add a preload of x_0 the force the sping exerts is, with x still being the _dampers_ change in length from full extension

F = k * (x + x_0)

Thus the force needed to compress the damper by x_1 which previously was:
F = k * x_1
has now increased to
F = k * (x_0 + x_1)
or in other words you have added a bias term of k*x_0 to the force.

The extra force of k*x_0 is the preload! That was added when you tightened down the preload collar and has nothing to do with the force needed to compress the spring further.
F = k * (x_0 + x_1) is the force needed to compress the spring by the preload x_0 and the extra compression x_1. However, the x_0 distance has been added in the preloading and you only need to compress it an extra x_1, hence the force required is still k*x_1.

Quote from tristancliffe :

People have tried to tell me my front wing is designed as a ground effect wing because it's large aspect ratio. Whilst I'm sure the wing does operate slightly in ground effect, I bet that's not the primary reason for the large aspect ratios. In fact, I don't really know why a lot of cars have large aspect ratios - the most efficient wing is long and slender (see gliders or passenger planes). Maybe it's because length is constrained by the regs, so they go deeper looking for downforce.

I think you've got your definition of aspect ratio wrong. Aspect ratio is calculated as (span^2)/wing area, so a long, thin wing (like you'd find on a glider) has a very high aspect ratio. The wings you describe for your F3 sound like low aspect ratio wings, having short span and long chord.

Higher aspect ratio wings are more efficient because the induced drag is reduced. Induced drag is caused by the wing-tip vortices of any finite-span wing creating a downwash region between the wingtips, hence changing direction of the lift and drag vectors. A component of the lift vector now acts to cause drag and a component of the drag vector acts against the lift. The wing-tip vortices of wings close to the ground are disrupted by the presence of the ground and the induced drag effect is smaller (search for the Ekranoplan to see this in action!).

What this means is that, for wings close to the ground, the effect of a high aspect ratio is already provided by the ground! Of course, having a high-aspect ratio wing will help further, but it's not so important as providing maximum lift.
Another nice feature of low aspect ratio wings is that their stall behaviour is much more gradual than a high-aspect ratio wing.

Getting back to topic...I think you're right about suspension preload settings. Most of the sites I've found dealing with bike suspension suggest that preload is used to change the ride height of the bike and should be adjusted with driver weight, etc... If a spring is linear then the force required to compress it won't change with compression.
The only effects of changing preload should be to change the ride-height of the vehicle and to alter the static position of the bellcranks, as you've already noted.

Believe it or not, I think the reintroduction of refuelling was meant to 'spice up' the show by adding a more strategic element to the racing.

However, I completely agree with you!

Quote from BuddhaBing :

I don't know the details of how netKar PRO generates force feedback but I strongly suspect that the self-aligning torque generated by the tyres is at least factored in and may in fact dominate.

The selt-aligning torque should be a factor in calculating the feedback torque, but there should also be a component from the product of the longitudinal wheel force and the scrub radius.

Sit in the pits in LFS and turn the wheel from side to side. You should find very little resistance because the wheels are free to roll. Now put the brakes on and try again...it will be much harder because you're now trying to roll the wheels against the force of the brakes.

Quote from ATC Quicksilver :

I still think Alonso should be faster, or at least more intelligent with his decisions and comments. I want to know how he brought 6 tenths of a second with him when he joined Mclaren, its not like he took them from Renault.

I think I agree with you, but it does seem that some drivers are capable of getting more out of teams than others. Take Damon Hill, for example. Now I realise that he isn't a truly great racing driver, but it seems like every team he was part of during his career (with the exception of Brabham in 1992!) improved leaps and bounds while he was with them, then failed completely after he left. Williams were already good when he joined, but Arrows seemed like a different team in the second half of 1997, then Jordan took their first win in 1998 and were challenging for the title (with Frentzen) in 1999.

I'd say yes, for tracks only. I know I seem to be in the minority in LFS, but I really like driving on real-world tracks. I couldn't care less about the cars being fictional as long as there's a good mix of different types and they're representative of real-world equivalents.

However, I was so desperate to drive a real-life track that I actually bought rFactor...with disappointing results!

Limiting mods to offline doesn't really make sense. Who is going to create a mod if it can't be raced online? Obviously allowing online mods does create some difficulties but for modding to be useful it has to be allowed online.

Quote from ajp71 :

What possible advantage can there be in bringing the heat up, assuming the ignition temperature stays the same you just make your heat engine less efficient.

I'm afraid I don't think I'm allowed to tell you that It's only an issue for Diesel engined road cars in any case.

Quote from bbman :

I heard the exact opposite, which apparently is the reason they have to use the heavier steel block instead of using aluminium...

No, Diesels run cooler than petrol engines. The reason for the heavier block is that the cylinder gas pressures during combustion are much higher in a Diesel than a petrol engine.

I'm not actually sure why Diesels run cooler than petrols...OK, they generate less heat, but what's to stop the manufacturers reducing the cooling to bring the temperatures back up? I've run tests on a Diesel engine where I found significant benefits to running it hotter.

Quote from Forbin :

That's exactly my problem with recent games, they go for the movie look rather than the realistic look, probably because it's easier to do and looks flashier to Joe Schmoe.

Well, you're displaying the game graphics on a device rather similar to a movie screen. It's a problem of dynamic range. The human eye can see brighter whites and darker blacks than can be displayed on a CRT or TFT. You can either compress the whites and blacks to fit into the CRT/TFT dynamic range (like LFS), making the lighting look flat and dull or you can attempt to fool the eye by using HDR rendering and a small amount of bloom.

Neither is 'realistic', they're just different ways of attacking the same problem.

Watch the 'Tearing up the Track' video on IGN...if you still think LFS looks better, I think you're deluding yourself. Of course, the cars don't move very realistically, but the graphics taken on their own are stunning.

Banning refuelling would be the first thing I'd do to improve overtaking. You want to get past someone? Do it on the track.
I think you'd suddenly see a lot more overtaking manouevers if the drivers knew they couldn't rely on pit stops to get past people in front.

Quote from J.B. :

If an engine concept from 1892 is the motorsport industry's idea of a future propulsion technology then I'm worried.

So what do you think should be a 'future propulsion technology'? The electric motor was invented in 1873 and the Otto cycle engine (i.e. petrol/gasoline) was developed in 1876. Diesel is the new kid on the block!

Quote :

And about WTCC: so SEAT is telling us that diesel is better than petrol because a turbo diesel beat an NA petrol engine? I'm eagerly awaiting their report on apples being better than oranges.

It's not necessarily about saying that Diesel is better than petrol, it's about breaking the public perception (particularly in America) that Diesel engines are for tractors or lorries. In the short/medium term, it looks like Diesels are the next big push in the automotive industry...they offer similar performance/ecomomy to gasoline hybrids without the cost and complexity of the hybrid drive.

The Audi R10, JCB Dieselmax Land Speed Record and the SEAT Diesel are all recent examples of a desire in the industry to promote Diesel as a modern technology. Diesels have come a long way since the development of common-rail high-pressure fuel injection systems.

Quote from Becky Rose :

"Fantastic start by Hamilton!" the UK race spokesman (I refuse to acknowledge his as a commentator any more) screamed as Lewis slipped down the order.

I was especially amused to hear them all talking about what an awful start Alonso got. Looking at the replays, it seems like both McLarens had bad getaways, the only difference was that Hamilton only had one fast-starting car behind him.

Still, the result was nice

Quote from shiny_red_cobra :

My dad says it could be that the cap on the gas tank may not be allowing air to go through like it used to, meaning there is slightly less air pressure in the gas tank, which could cause gas to stay in the tank instead of going to the engine. Could this be it?

Surely this would cause a constant loss of performance? I don't see how a blockage in your tank vent could fix itself once your engine has warmed up. In any case, modern cars usually have some sort of fuel tank breather connected to the engine air intake.

If the engine warning light is illuminated then the loss in performance might be a 'limp-home' mode which engines use to allow the driver to get to a garage for repair. There could be any number of reasons for this...it's probably best to take it to a garage so they can interrogate the ECU.

Quote from LazLoW :

I think it's kind of stupid in the regulations to have a reverse gear, so they put a shitty one in that doesn't work. If it doesn't work then why is it in the regulations? They must have updated them so it definatly works when you need it, not a fault due to the obsession of saving weight.

It does work, it's just not designed for continuous use.

Quote from ajp71 :

EDIT - I had forgotten to switch to Direct X, problem gone now, just need to figure out why I've got no FF

Have you got the following lines in your 'core.ini' file?


The numbers in here are the defaults set by the GPLPS installer. I've not tweaked them in any way, so don't worry if the numbers don't match. The important thing is that the lines exist and that allow_force_feedback = 1!

Quote from ajp71 :

Ah right sounds like that's what I want

Downloading...

Oops! It doesn't include GEM and iGOR...very sorry. I've just checked and I installed them seperately from the GPLPS installer. The d/l link for the latest GEM/iGOR is here:

http://gem.ebi-service.de/GEM/GPLS_0424.exe

Sorry about that...hope I didn't confuse anyone!

Quote from ajp71 :

No the 2004 demo (and original demo) is identical to the full GPL with one difference, it only has 1 track, you can change it into the full version by just copying the track folder from your CD (no need to install the folders are loose on the disc). I used the 2004 demo + original tracks online without any problems, now I wish to install GPL again (and GEM) so I'm wondering which is the easiest solution.

Well, the GPLPS installer includes GEM and iGOR so I'd still say it's the easiest way to do things. Oh, and the GPLPS installer comes with big updates to 10 of the 11 original tracks.

I'd strongly reccommend using the GPL installer from this thread at RSC:

http://forum.racesimcentral.com/showthread.php?t=288457

You must have the original disc to install the game (it's not a stand-alone complete download) but it makes sure you've got all the relevant official patches (up to 1.2.0.3, I believe) as well as some unofficial patches (Direct3D rendering and 'carsound' patch) and all the latest car and track updates.

It's a big download but IMO it's worth it if you're new to GPL and haven't got all the little bits individually.

Quote from MAGGOT :

What on Earth are you talking about? That was a generalisation, not a personal attack.

So if I wrote "Weird, Canadians are usually not dumb. " in response to one of your posts (or a comment on one of your posts) you wouldn't be offended?

Quote from wsinda :

"Basic food and shelter"? A prison isn't a B&B. It's about taking away someone's freedom, and that causes suffering. If that suffering is your sole goal of imprisonment, then your view of punishment is a bit... outdated.

Outdated it may be, but that doesn't mean it's wrong. Criminal acts require punishment, otherwise the justice system is meaningless. How can you punish someone without causing them some degree of 'suffering'?

Quote :

I'm still wondering how you can concede that abuse is barbaric, but maintain that execution is not.

I don't call a quick death barbaric. I must admit that I'm a little uncomfortable with the use of the electric chair as a method of execution, but I don't even see that in the same league as sustained abuse.