This surprised me, the car in the video below has these specs:
-800 kg total weight
- low inertias (800 pitch, 1000 yaw 300 roll)
- ~1.5G pulling ''slicks'' (slip peak probably between 7 and 9 degrees)
- lowered centre of gravity by 7cm

Why? Just a bit of an 'extremes' test, tends to help understand certain things better.. And I expected it to still be impossible to drive such a car over the limit in rFactor. Its not far off a 'downforceless' 1979F1 car in a way..

The rest is the same Corvette, i.e. same suspension (though twice as stiff as the weight is nearly halved!) same dampers, rollbars etc etc.. Yet it was quite hard.. but not impossible!

http://www.youtube.com/watch?v=ouexJ7MKMe4

Around the 'centre' (i.e. going straight) it felt harsh but once in a slide, not too bad.

Woah you dug this old thread up Leo! Thanks for the insight.. Not all games 'poll' the controller at the framerate per se.

What does help a lot is that 'render ahead' tweak (set to zero) in various ATI or Nvidia 'tray tools' type things. Roughly made the rFactor lag go from ~0.25 to ~0.125s, including all measurment lags. There is a distinct difference from sim to sim though.

Input lag should be a priority, at 0.25 seconds, although an extreme example (some games at ~30fps) you simply are not driving the car.. It is more like telling someone what you want them to do with the controls..

Hi readers,

I'm assisting a Romanian student who is doing a research project on small cable companies (i.e. TV / Internet / phone type providers). Part of the research is a study of the European situation.

Finland it seems, has quite a few smallish providers. We have a list of possible companies, but now we need a Finnish (speaking) guy or girl who is willing to spend a few hours gathering just basic information about a few of these companies. Things like:
- amount of customers
- amount of employees
- type of products offered
- involvement in local activities

We anticipate that in 5 hours it should be possible to find these superficial details for 3 or 4 companies. We can pay what we get paid, about 10 euro per hour.

Are you Finnish, somewhat aware of the cable company market and good with google, not afraid of perhaps making a phonecall or two? And can you use 50 euro?

Send me a PM!
/Niels

Looks like a step up! But still not fast enough, from the ultimate standpoint. And knowing Frex, it won't come cheap.. Plus the many thousands of euro that patents cost must be earned back.. Don't count on this getting affordable

And the 50.000 one has to pay to Immersion for the licensing.. yay.. Brave of SHige to invest though, easy to talk, brave to do things like this.

Last edited by Niels Heusinkveld, Sun, 3 Jun 2007 14:47.

doh!

Here is a better deal,

Antec SLK3000B (boring, but neat, front and rear 120mm fan

but!! this leaves you with cash for a Scythe Ninja heatsink. That will cut noise and temperatures in half.


That is what I'd do!

Edit: assuming your system is AMD64 or P4 / Core duo type, the heatsink won't fit on old socket A Athlon xp systems..

Last edited by Niels Heusinkveld, Wed, 30 May 2007 23:03.

Understeer is easy to define.. But I don't think we can find a unanymous (sp!) way to define when to call a *car* understeery...

http://www.youtube.com/watch?v=AM3uiUQlh4c

this is a normal driving onboard thingy with monotone voice comments..

Weird eh! I went from hating ISI to 'seeing possibilities' .. Perhaps when the car is released there might be a little less (ISI)hate in the world..

Its not too bad in the 'Vette But you have to be on your toes and time the straightening of the wheel well.

http://www.youtube.com/watch?v=rOVKDgJajFc

Wazza!

The rFactor rambler is back. I may have discovered a relatively vital thing that is missing in the ISI physics engine. The tyres do not flex laterally, i.e. in the 'sideways' direction when driving.

This lateral movement of the contact patch can easily be a few centimeters and I suppose it would act much like a spring; with more lateral force, the contact patch moves more.

Now the tricky bit; to what does this translate, car handling wise? I found rFactor to not be half bad. Using the inertia values of the LFS FZ50 (thanks Bob.. ) its pretty 'slow' in yaw and easy to control, using better tyre curves and data. However, near going straight, things are quite immediate and snappy. When trying to come out of a left turn sideways, and flick it the other way for a righthander, there is an explosion of body roll and very very fast damper speeds are noticed. This can easily make it snap too much and make you loose control.

Would it help if there was lateral tyre flex? It sounds like it may. When going from a lefthander into a righthander, the tyre contact patches will move in lateral direction, sort of slowing the response (i.e. weight transfer) down a bit. It may just be more forgiving around the centre.

If I'm any sort of correct, that might .. might just be one of the main things that could be improved in the ISI engine!

Any thoughts on the handling influence of lateral tyre flex?

/Niels

Agreed, but that doesn't rule out the driver. I don't think you can rule him/her out completely but with LFS, some will find a car to understeer where others say oversteer, even with the same car setup..

I'm still thinking somewhere towards yaw angle. How easy the driver can change the 'heading' of the nose of the car, with any combination of wheel/pedal input..

Edit: not in response to Tristan

I actually am not too sure about understeer anymore!

If I want to enter a corner, steer into it, and find myself sliding straight on towards the outside of the corner, am I understeering? I used to think so.

Or am I just being silly trying to enter the corner at the speed I was trying? Hmm if I would go slow enough, even with tyres made from soap I could enter the corner without alledged understeer.

My question is basically, if a car can pull near its maximum lateral (cornering) G forces at any time when turning the steering wheel, can you call that car understeery? If my car does 1G in the turns, I enter a corner too fast and end up in the gravel traps after 'understeer', yet the telemetry shows that I did 0.99G laterally until I left the tarmac.. Then really the *CAR* wasn't understeering was it?

Or was it? Lateral G forces are just that, forces in a line from the left door keyhole to the right, 90 degrees from the rolling direction of the car. The greater the yaw angle of the car then, the more the lateral force will try to slow down and corner your car.. But I'm not quite sure on this..

What would a TRUE definition of understeer be!?

ah.. load sensitivity is based on load alone, there is just a contact 'point' in rFactor as far as I'm aware. This point can be made to have more or less grip with load changes, temperature changes, pressure changes..etc..

The two posters above, thanks! you have a PM

If I interpret them right, i.e. the main car inertias are 2064, 491, 2382 (pitch, roll, yaw). My corvette comes in at 1586,435,1942, measuring unsprung mass around the COG of the car, with a 3.3x1.6x0.6 meter solid block of sprung weight attached. I'm using those numbers with 5% of both sprung and unsprung inertia added, still a little lower than LFS values.

Interesting to see by all accounts!


The oscillation problems are solved, it turned out to be overly soft and undamped tyres, plus the physics engine with the car near or at 0km/h isn't going to be trustworthy. The weight transfer seems to be ok in ISI, the roll per G predicted by the suspension program is matched closely in the sim, as long as you take tyre flex into account..

Bob, you mentioned tyre load sensitivity when I said the rear tyres where a big more grippy? In ISI you can set base long. and lat. grip multipliers for the front and rear tyres. So if one thinks the rear tyres, with 40mm extra thread with are 3% more grippy laterally and 5% more longitudinally than the fronts, its easy to set. Load sensitivity is also set for fronts and rears separatly, you can do whatever you want, i.e. if I want load on the rears to make them loose that initially added grip, its possible..

At the moment the biggest advantage of LFS over rFactor is the smooth tracks in LFS. Most of the ones in rFactor are worse made to start with, plus the nasty fact of driving on what seems to be the polygons, really makes most of them ones to avoid. Barcelona comes with the game, and that is pretty smooth. Really makes the ride a lot nicer and more predictable..


Is there anyone reading this who wants to have a go at a pre release corvette? Especially if that someone has been tweaking the rFactor force feedback.. It would be nice if the FF tries to keep the wheels in the rolling direction, I'm not sure if ISI thought of that possibility with their FF code..

Thanks Bob!

Interesting about that inertia matrix.. One thing I'm sure can change the 'feel' of inertias, how progressive tye tyre model is. If its harsh with its transition between grip and slip, it might well feel as if inertias are low. In LFS its all slow and controlled, but that could just as well be an 'easy' tyre model and not high inertias..

How do i get that matrix for, say, the Fz50 ?

The documentation is great, well.. except for the fact that there is none.. The devs simply don't give a @$!#. Such a difference with LFS, where you can be sure the devs aim for realism in all departments.

I entered realish data. When 'realish' doesn't give results, I don't go deliberatly 'un-real-ish' because thats a road with no direction.. Some realish numbers used in that video:

- Weight and weight distribution
- power and torque and drag, plus friction giving accurate:
- 0..60
- 1/4 mile
- 150mph points (close enough)
- 0.98 G average on a skidpad as in the specs, instant G is about 1.1
- COG height is about 40% of the roof height, as consistently seen in a SAE document
- High slip ratio modelled; grip DOES drop off to 66% longitudinally but only at 4.5x slip; i.e. max wheelspin at a standing start type situations
- Slip peak and peak change based on a real tyre ~12..20% with load variations)
- Slip angle peak for the fronts is between 8 and 12 degrees from 0 to 800kg tyre load
- wider rears with lower side wall between 7 and 11 degrees from 0 to 800kg.
- rear tyres about 5% more grippy than fronts

Not too sure about:
- tyre load sensitivity... drops to 70% at 1600kg load, in an unknown way. Real tyre data shows about 90% load sensitivity at 5000 Newton compared to 1000Newton load, hopefully I'm somewhere near that..
- Inertias, always hard to do.. they're at about 1700 / 2100 / 425 (pitch / yaw / roll)
- Aero is simple, just a 'point' 2 meters in front of the rear axle, with the right drag coefficent.
- Using a great suspension generator tool, where you can input desired camber change and roll centre height etc, I went for 50mm high roll centre in the front and 100mm at the back, with the fronts changing camber a bit more with roll than the rears..
- Its not quite clear how to do friction; as the engine / driveline friction is entered as a torque, where it would make more sense if it would be a % of engine torque instead..

hahaha

Of all people though, I was up there with Tristan spouting my anger and hate towards ISI. I had the not so popular 'I hate ISI' MS Paint T shirt job at RSCnet.org, for which I'll be hated by the blinder rFactor lovers until death..

Then I got busy 'modding' (what a crap word) and even though the results where not great, it did show that at least half the crapness is due to poor input data.

Now this guy with a good Corvette model wanted a physics editor, and I thought such a car might work relatively well, plus there is some data available.

Its really not THAT bad! I've improved the tyre curves and the car is somewhat close to the real specs, and drifting it around is really almost as easy as LFS! Yes I LOATHED ISI before, but it is unfair to judge simply by the available games and mods.

Next to that its quite a learning experience messing with the physics in an attempted 'good ish' way. It is kinda frustrating with LFS, though understandable, that the physics evolve slowly. A control freak like me wants to mess around with the numbers..

a short video, even the poor replay code shows body pitch / roll.. and surely this doesn't look all that far removed from planet earth?

http://www.youtube.com/watch?v=JZDu7oXAEm8

/Niels

The problem is with roll, not with pitch. Or at least I think it is a problem..

I tried a few different roll inertia values from a bit low 250 .. (what is that .. kg*m2?) to really high 750.. It didn't really change what was fundamentally happening all that much visually, just the speed of the oscillations visually.. I can MOTEC a few different inertia numbers..

I tried it in LFS and its somewhat tricky because if you're not sliding at near 90 degrees sideways, there is a weird 'yaw jerking' going on when you stand still. One time it seemed to go well, using the RB4 with a similar ish setup as my corvette, and it wasn't nervously roll oscillating at all..

I know that sometimes near standstill, physics engines aren't too trustworthy, but I encounter it when driving as well, everytime it rolls it feels a bit strange..

Now ISI has felt strange to most of ''us'', however it would be nice to get some more understanding of it

Total Lateral Load Transfer Distribution :S The RSCnet thread is about a program that shows and explains that, I had not heard of it in my life.. If above 50%, more load is transferred to the front for 'understeer' and <50% makes it rear biased 'oversteer'..

What do you mean with the 2nd moment along the roll axis? Looking at a frontal view and the moment (torque) by the force (cog) on the tyre contact points?

In a side view of the car with 50/50 weight distribution, the distance from the COG to the tyres is 1.34 meter (half the wheelbase). In a front view it is 0.77 meters (half the track). I suppose that this means the forces on the suspension from roll will be greater than those of braking/acceleration, seeing as the car pulls ~1G in both directions.. But thats about 70% difference, I doubt that explains it.

Hi guys,

I figured and hope there might be a few LFSforum lurkers here, interested in car physics, that steer WAY clear from the RSCnet rFactor forums..

By lack of somthing much better, I am busy building a Corvette C6 for that game, hoping to make it relatively good. I'm doing it as seriously as I can, even though I lack skills in some areas. Armed with MOTEC and a few tools, I hope to make it work.

Now some have suspected dodgy weight transfer / roll behaviour in ISI physics. I've stumbled on to something that I can't figure out. If you'd like to have a look, the thread is here, but skip my first post, as I obviously made a mistake there.

http://forum.rscnet.org/showthread.php?p=3449815#post3449815

The stiffness of the rollbars needed to get a certain roll angle seems way off. The oscillations from roll are such that it seems that the dampers don't work when comparing it to pitch damping..

Some odd stuff, hopefully interesting enough for a few of the Guru's here to have a look at?

/Niels

The picture doesn't work for me, although I can imagine how that must look.. Put very mildly, I tend to laugh out loud when I see such a car on the streets.. Edit: it works now. Well, it could be worse actually!

a 7600GT uses about 35 Watts. I don't know if there even is a GTX version but it won't be a lot more..

You can run a Core Duo chip with a x1950xt / 7900xt perfectly fine on a good 300W powersupply. Recently some people managed to draw 600Watts for their pc. It had:

- Two amd Fx74 dualcore processors (i.e. no quad core single cpu, those are likely to be more efficient)
- two 8800GTX cards
- the usual rest

When they put those cards in a Core duo (or was it a quad core..) the load already dropped to 500W. How many people are crazy enough to get TWO 8800GTX cards? With one you'd be looking at 380W, and that would be a top of the line pc!

Check a list of configurations here:
http://www.silentpcreview.com/article28-page4.html

The Pendium D 950 is a hotter chip than todays dual core ones, and the x1950xtx is a pretty hot card. Total power drawn? 256W.

If you focus on brands:
- Fortron
- Enhance
- Seasonic

you'll find their 300W powersupplies to outperform MANY of the 500 / 600 / 700W rated cheap models.

Powersupplies is one of those areas where marketing and lack of legislation made everything go beserk..