I was playing the netKar Pro demo today and the first thing I noticed was the FF. It was excellent. The way it gave a texture to the road, how it lost most resistance when the front wheels were sliding, how rumble strips on curbs felt, every thing. LFS's FF is nowhere near this good. You can feel the road, and what the car is doing, but not to the level you can in netKar. even if these features are in LFS, they are very very subtle.
netKar level feedback
Now don't know how netkar does it's FF, but if it's like any other sim out there, it uses prescripted FF Effects, like if yu go on curbs, it rumbles, or of you lose traction of the front wheels, it lets go.
Now, LfS is different because it doesn't use these canned FF effects, but calculates the FF from the forces that apply on the front wheels.
Now, allthough more realisticm LfS's system has one "flaw": while all the other sims use fake FF Effects to simulate other movements (for example the rattle. actually, it's not the wheel that is rattling but the whole car), LfS lacks those.
Now, LfS is different because it doesn't use these canned FF effects, but calculates the FF from the forces that apply on the front wheels.
Now, allthough more realisticm LfS's system has one "flaw": while all the other sims use fake FF Effects to simulate other movements (for example the rattle. actually, it's not the wheel that is rattling but the whole car), LfS lacks those.
Actually netKar allegedly doesn't use prescripted effects for the FF.
As ColleusRattus says above: the feeling netKar gave me after I sort of rationalized it was that it transmitted vibrations/forces via the steering column that you'd normally feel coming from the rest of the car.
As ColleusRattus says above: the feeling netKar gave me after I sort of rationalized it was that it transmitted vibrations/forces via the steering column that you'd normally feel coming from the rest of the car.
+1, love the FF in Netkar, esp the feel of understeer entering a corner, you can really get an idea of the front tyres being pushed into the corner. This has a lot to do with the sound feedback as well.
Absolutely, nK's FF is one of the best I've experienced.
Nice avatar btw Al :up:
Nice avatar btw Al :up:
I prefer the way the steering loads and unloads in LFS personally. nKp has vague moments which I don't think are quite right, although that could just as easily be physics as FF.
I'm not too fond of the wheel going light on understeer, though I don't really have the racing experience to tell if that happens in reality or not. It just feels kinda weird, especially if you have to push past the point of highest resistance to get best cornering results...
It does so very much, even in street cars, although much more noticeable in cars without power steering.
Only car you probably won't feel a difference in is a BMW.. as that has girly (ie: light enough not to break a nail, too light to feel the road properly however) power steering and it feels like that all the time
Regards,
Ian
#9
- atledreier
without having measured the torque neede to hold a turn while the car is understeering, I'd say the 'going light' feeling is the fact that it's not taking MORE torque to hold the turn beyond a certain point. Akin to the 'car speeding up on grass' theory.
+1
I've said it all along, the FF in nKPro is the best in any sim, ever. Everything feels so natural, and not a pre-scripted effect in sight.
My only minor complaint would be that the cars don't feel quite as weighty as the LFS ones, but i can forgive that as the overall effect is fantastic.
I've said it all along, the FF in nKPro is the best in any sim, ever. Everything feels so natural, and not a pre-scripted effect in sight.
My only minor complaint would be that the cars don't feel quite as weighty as the LFS ones, but i can forgive that as the overall effect is fantastic.
I subscribe to that theory. I can't quite work out the physics if the steering actually became lighter when understeering. At best I could see the torque leveling out. What forces suddenly disappear if it actually drops?
Driving a car i netkar and lfs gives me the same feeling... rfactor is a different story... 
netKar is going to be a god racing sim!! The flatspot shaking is extremely breathtaking. btw its not there in v1.0.2 but will be back in v1.0.3 (due in September) Hope LFS will get flatspot FF... 
+1 for flatspot FF
netKar is going to be a god racing sim!! The flatspot shaking is extremely breathtaking. btw its not there in v1.0.2 but will be back in v1.0.3 (due in September) Hope LFS will get flatspot FF... +1 for flatspot FF
I can agree with the force levelling off, but that is not what happens in nKPro. I just tried in the F1600, and in a corner you can simply throw your wheel in one direction and it goes completely limp, staying in this position forever. The tyres still provide relatively good grip and get me through the corner safely, but for unknown reasons the wheel has no resistance whatsoever, as if I was aquaplaning. 
Shame it's effect-based.
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.
Here's a typical graph showing self-aligning torque (SAT) as a function of slip angle and tyre load. As shown in the graph, the torque increases to a peak and then falls off to zero. If SAT is used to generate FFB, the steering will feel increasingly light as SAT falls off past peak.
The peak in the SAT curve generally occurs at a smaller slip angle than the slip angle which generates maximum lateral force. This means that SAT starts to fall off even before the optimum slip angle for cornering is reached. By the time the car starts to understeer, the SAT acting on the tyres will already be well into the post-peak part of the curve.
lol i've been asking for this for like 4 years now.. 
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.
Found something rather interesting there while trying to understand what exactly self-aligning torque is:
http://www.engr.colostate.edu/ ... ing%20Tire%20Modeling.pdf
While I still can't completely wrap my head around it, one thing I question myself is why nKP and LFS are so different in that regard. Up to the apparent SAT limit they feel quite similar, but then they start to do completely different things. nKP goes limp while LFS doesn't really do anything at all at understeer (if it's not FWD throttle induced). Who is right? Or is neither, and we should get a little bit of easing up but not as exaggerated as in nKP?
http://www.engr.colostate.edu/ ... ing%20Tire%20Modeling.pdf
While I still can't completely wrap my head around it, one thing I question myself is why nKP and LFS are so different in that regard. Up to the apparent SAT limit they feel quite similar, but then they start to do completely different things. nKP goes limp while LFS doesn't really do anything at all at understeer (if it's not FWD throttle induced). Who is right? Or is neither, and we should get a little bit of easing up but not as exaggerated as in nKP?
Good points; and this last part really impresses most people that don't know about LFS.
It's interesting to play with the brake while turning the wheel when not moving, modulating it small bits at a time. You can "feel" the brakes grabbing different amounts, and notice when you're slipping them a bit using slight brake pressure. Pretty cool alright.
Holy cow, that is a SWEET document, nice find! Some interesting graphs and points about different tires and scads of other great stuff.
I can't understand how someone who can write that doc cannot spell "brake" though :doh:
edit: the graphs on P 13/15 don't show the drop to zero for the SAT, but rather a fall off that levels off fairly quickly; so I suspect that your suspicion of the "truth" being somewhere between LFS and NKP is probably true.
Had that document for nearly 2 years... but Foxit reader won't open it now. Really don't want to switch back to that Adobe Reader bloatware. Bah.
Yes, that's true for a lightly loaded tyre. However, as load increases (e.g. under heavy braking or hard cornering i.e. in race conditions), the fall off is generally quite steep and SAT can even, in some cases, become negative. Here's a graph from some engineers at Hankook showing this:
(image taken from "Role of Tire Modeling on ... Choi, Hankook Tires, 2001).
If I were a betting man, I'd wager that the differences between netKar PRO and LFS are down to the way in which each models pneumatic trail. Pneumatic trail is distance between the centre of the wheel and the pressure centre of the tyre's contact patch and represents the location where lateral force acting on the tyre is applied. Since this location is offset from the wheel centre, when lateral force is applied to the tyre it generates a torque which causes the wheel to self-align (as long as pneumatic trail is behind the centre of the wheel). This is the self-aligning torque we have been discussing. Due to the dynamics of the contact patch, pneumatic trail varies with slip angle and load as shown in the following graph taken from the same paper I cited above:
Now, if LFS holds pneumatic trail constant, then LFS's SAT v slip angle curves will have the same shape as its lateral force v slip angle curves. If this is the case, and since it's generally accepted that the LFS lateral force curves do not exhibit much post-peak fall off, then LFS SAT curves will also not exhibit much post-peak fall off. This seems to be consistent with LFS's "force leveling off" behaviour described above.
could someone please clear one thing up for me ? from my understanding sat need a certain degree of long slip otherwise there wont be an arm to act on yet those curves never refer to any long slip
I was kind of wondering the same thing, but I don't have an intuitive understanding of all this yet... although that doc is helping a lot.
It ties together all the fragments I've learned from Todd and others....
It ties together all the fragments I've learned from Todd and others....
The arm is called the pneumatic trail. Pneumatic trail is a property of the tyre and depends on the dynamics of the tyre's contact patch.
Self-aligning torque is derived from the pneumatic trail and lateral force acting on the tyre as follows:
Mz = -tp * Fy
where Mz = self-aligning torque, tp = pneumatic trail and Fy = lateral force.
Self-aligning torque is derived from the pneumatic trail and lateral force acting on the tyre as follows:
Mz = -tp * Fy
where Mz = self-aligning torque, tp = pneumatic trail and Fy = lateral force.
netKar level feedback
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