That's from the x car or whatever sim someone kindly posted earlier in this thread.
http://www.lfsforum.net/attach ... d=103594&d=1270666115
Look at the valley stemming out from the origin and going off at some diagonal. According to your graph if you increase slip angle and slip ratio together at a certain rate, the tire can not make nearly as much force as it can in some other direction. This is utter nonsense and ignores the fact that out in these areas all you really have is a big blob of rubber with some potentially odd vertical force distribution on top of it sliding across the road. Why would this exhibit behavior anything like in this graph?
Bottom line: That sagging area in the back and the valley leading up to it should not be there at all. I don't understand why you want a saddle shape in the first place. It shouldn't be a saddle...
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AndRand, I still haven't found the time/inclination to get fully into this with all the details of what's wrong. Maybe I will later today.
For now, if you are to plot lateral or longitudinal force by itself rather than the combined force magnitude, what you should get is a shape like one quadrant of this:
http://img215.imageshack.us/img215/6734/lateralforce23.jpg
Here the peak is outrageously high compared to the rest of it (garbage in/garbage out), but in essence this is what you ought to get. Again, you'd only be plotting one quadrant of this, but the point is the worst that ought to happen is at the origin you'd have 0 force which then climbs to a peak roughly some distance away from the origin (which you could trace with an ellipse) which then fans out into a fairly level surface. Unless I'm having a brain fart right now, both lateral and longitudinal ought to look something like this in terms of basic shape with the lateral being rotated 90 degrees to this one.
The combined/resultant force graphs you've been posting are just the vector sums of the other two graphs, which ought to have the same basic shape rather than something where you've got a bump above either of the pure slip force peaks and then a huge dip at some combination out in the combined slip area. Juls was right to point out that when you look at the graph you've got to think about what it's really saying (in his braking example where you suddenly lose a lot of force and then gain it again).
AndRand's last picture http://www.lfsforum.net/attach ... d=103635&d=1270747270
Keep in mind that the bottom graph is mostly, if not entirely, well within the traction capability of the tire. On your other graphs this corresponds to the area inside that initial cone climbing upwards out of the origin. This is why you can find the combined force being greater than either of the pure slip forces (the distance from the origin to any point on any of the curves is plotted as the height coordinate of AndRand's combined force graphs).
EDIT: I wrote "Keep in mind that the bottom graph is mostly, if not entirely, well within the traction capability of the tire." The places that are passed the traction limit are where the curves hook back in on themselves as slip ratio is increased beyond the peak.
For now, if you are to plot lateral or longitudinal force by itself rather than the combined force magnitude, what you should get is a shape like one quadrant of this:
http://img215.imageshack.us/img215/6734/lateralforce23.jpg
Here the peak is outrageously high compared to the rest of it (garbage in/garbage out), but in essence this is what you ought to get. Again, you'd only be plotting one quadrant of this, but the point is the worst that ought to happen is at the origin you'd have 0 force which then climbs to a peak roughly some distance away from the origin (which you could trace with an ellipse) which then fans out into a fairly level surface. Unless I'm having a brain fart right now, both lateral and longitudinal ought to look something like this in terms of basic shape with the lateral being rotated 90 degrees to this one.
The combined/resultant force graphs you've been posting are just the vector sums of the other two graphs, which ought to have the same basic shape rather than something where you've got a bump above either of the pure slip force peaks and then a huge dip at some combination out in the combined slip area. Juls was right to point out that when you look at the graph you've got to think about what it's really saying (in his braking example where you suddenly lose a lot of force and then gain it again).
AndRand's last picture http://www.lfsforum.net/attach ... d=103635&d=1270747270
Keep in mind that the bottom graph is mostly, if not entirely, well within the traction capability of the tire. On your other graphs this corresponds to the area inside that initial cone climbing upwards out of the origin. This is why you can find the combined force being greater than either of the pure slip forces (the distance from the origin to any point on any of the curves is plotted as the height coordinate of AndRand's combined force graphs).
EDIT: I wrote "Keep in mind that the bottom graph is mostly, if not entirely, well within the traction capability of the tire." The places that are passed the traction limit are where the curves hook back in on themselves as slip ratio is increased beyond the peak.
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:doh:
Right you are
Juls: You've hit the nail on the head. Also the fact that at some non-zero combination of slip angle/ratio the force capability of the tire increases beyond that of pure slip is a giveaway that something is goofy. Try drawing a friction ellipse type of graph that shows that happening. It'll be some bizarre egg shaped type of thing where the radius is longest at some nonsensical diagonal angles. I've never seen that happen in any tire data.
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Maybe what you could do when you get access to the file is check the max combined force in pure slip in either direction, then see if there are any values off either axis that are higher than this maximum value. In the exaggerated diagram this is clearly not the case, but perhaps for the other it is. If so, there is a point to be made about something that I'll get to.
Looking forward to seeing your new graphs. I have a question concerning my attachment. The red circles correspond to the highest force possible in pure slip (unless the friction ellipse turns into some kind of off-axis egg shape). It's difficult to tell from the graph, but is any force in the region with the blue circle higher than the red circles? To me it appears to be, but I'm not sure.
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Only have a minute now so I'll just address this:
Imagine slip ratio 0 and slip angle 10. Lateral force is 1000. What are Fx and Fy?
We have in this case:
Fy = 1000
Fx = 0
The resultant of a 2D vector is its length. In this case, it's 1000.
The pure slip force is the combined force when you're moving directly along one axis with the other axis at 0.
My assertion that
is therefore correct.
Once you move off of both axes into the middle area you are in a combined slip state and your statement is correct.
Perhaps you could try doing this with 2 flat curves that do not have any drop off after the peaks and see what the combined slip area looks like. I'm curious if the hump in the middle goes away and the nose-dive at high slip angle and ratio disappear.
Imagine slip ratio 0 and slip angle 10. Lateral force is 1000. What are Fx and Fy?
We have in this case:
Fy = 1000
Fx = 0
The resultant of a 2D vector is its length. In this case, it's 1000.
The pure slip force is the combined force when you're moving directly along one axis with the other axis at 0.
My assertion that
is therefore correct.
Once you move off of both axes into the middle area you are in a combined slip state and your statement is correct.
Perhaps you could try doing this with 2 flat curves that do not have any drop off after the peaks and see what the combined slip area looks like. I'm curious if the hump in the middle goes away and the nose-dive at high slip angle and ratio disappear.
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I disagree with the interpretations you've put forth concerning the force resultant, or I'm misunderstanding what you're plotting. This is something along the lines of the magnitude of the total force ((Fx * Fx + Fy * Fy)^0.5), right?
If so these are not right:
http://www.lfsforum.net/attach ... d=103471&d=1270423573
If we start at the front corner at 0,0 slip and trace along the left axis, the force rises and somewhat levels off. I assume this is combined force in slip angle, which in this case is simply the lateral force. If we go back to 0,0 slip and trace up and to the right, the force climbs and then dips a bit. This I assume is slip ratio, with the corresponding pure longitudinal force. So far so good.
But what happens when both slip angle and slip ratio are very large at the same time? This is the far corner of the graph where F combined has plummeted from as high as 950 or 1100 in some places (pure slip along the axes as described above) clear down to about 400.
The statement: "(Fy is almost flat when off the limit)" is not correct. It takes a huge plunge into nothingness when you have lots of combined slip. If anything, it should somewhat level off somewhere if the forces were being trimmed to a friction ellipse rather than whatever you did there
There's nothing forgiving at all about any of those tires. They would feel truly bizarre and rather impossible to drive, I suspect.
If I'm misunderstanding what was plotted, please explain.
Another issue are some of the earlier plots in addition to these. Slip ratio of 12 or 15 or something with large slip angles is not going to result in such large lateral forces. It'll be almost completely longitudinal even out to 90 degrees slip probably. The directions of the final force vectors are very far off everywhere in the combined areas. Take a look at the top graph you posted here:
http://www.lfsforum.net/attach ... d=103383&d=1270299686
See what happens to Fy (lateral force) at only 12 degrees slip angle and slip ratio of 1. It drops substantially. This isn't reflected remotely accurately in your curves yet, although some of the shapes in some places are starting to look a bit better in general. It's not so simple to think purely mathematically about this and come up with the right answer. Not for me at least. Most people must think about the underlying physics and come up with the math afterward, but perhaps you'll turn out to be an exception.
You haven't quite reached the point to charge consultant fees, but keep at it and maybe you will
EDIT: One more thing for you to look at and think about. Check out the force resultant hump that pops up towards the middle of the combined slip area, especially prominent on the "least forgiving tire." Can you think of any physical reason why at this point where the tire is completely sliding there would be an area where if you altered slip ratio and slip angle just a bit this way, then just a bit that way, the force would suddenly rise way up and then fall off again? It's wise to think about what the math model is producing in physics terms. Really think about what the tire and rubber is doing at each spot on the curve and why the forces might be changing as shown.
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AndRand's post:
http://www.lfsforum.net/attach ... d=103383&d=1270299686
This is exactly what I meant by the combined force screwing up the curves. You can't just say "slip ratio is 0.05 and slip angle is 3" and then find the forces by looking them up on their respective pure slip graphs (this is a friction square approach with the friction circle limiting added on top of it as a separate step). The curves change dramatically when you have both slip ratio and slip angle occuring at the same time even when you're well under the peaks.
Many sim developers historically haven't bothered to emulate this. It has a profound effect on the controllability of the car. A sim with this done well is also a lot more fun and realistic to drive
This is an area where when done well, "easier = more realistic" rather than the other way around.
http://www.lfsforum.net/attach ... d=103383&d=1270299686
This is exactly what I meant by the combined force screwing up the curves. You can't just say "slip ratio is 0.05 and slip angle is 3" and then find the forces by looking them up on their respective pure slip graphs (this is a friction square approach with the friction circle limiting added on top of it as a separate step). The curves change dramatically when you have both slip ratio and slip angle occuring at the same time even when you're well under the peaks.
Many sim developers historically haven't bothered to emulate this. It has a profound effect on the controllability of the car. A sim with this done well is also a lot more fun and realistic to drive
This is an area where when done well, "easier = more realistic" rather than the other way around.The equations you'd use for an ellipse would be different of course, but it's the same concept. I couldn't tell you how close they are to reality since I don't use these concepts in my own modelling and so haven't gone looking for an answer to this one.
The lateral/longitudinal force dependence approach used depends on how it's modelled of course, as would a split in peak lat/long force (ellipse effect at limit). At one extreme with FEM tire modelling as is done at tire manufacturers, I doubt there is any of this done directly at all. The forces come directly from the stresses at each node which should produce all this without needing to try to account for it with separate equations. In the context of other models I'll leave that to others to find, but a similar thing happens. That's getting a little too close to discussing how my stuff handles things and I don't want to post that stuff publically.
As W126 pointed out, you'd need data at lot of different loads for the network to learn how to predict forces at non-tested loads. I doubt 2 loads would be nearly enough, and you'd need full Fx/Fy testing. Multiple loads at lots of slip angles and slip ratios, then multiply that again by the number of camber tests, then again by the number of different air pressures, etc.. I'm just guessing here, but supposing if Pacejka or another model couldn't be made to fit a big set of data like this, the network might be able to learn the patterns that are too complex for humans to tune. I've never seen a set of data for a single tire that's this comprehensive. Even combined data is fairly rare and I don't recall seeing any for multiple loads on a single tire, let alone all the other stuff. It's probably been done, but with such an expensive test it's unlikely to be posted for the public in a paper somewhere. (If anyone finds some, please point me to it.)
I haven't read any papers on neural net tire models. It was just a thought that occurred to me some years ago and then eventually I ran across a paper or two mentioning their use. So your point could very well be right, but I'd suspect you'd need huge, expensive data sets.
Just gave that sim you linked to a shot. Think I'll pass on this one, but I can see it being interesting to people that want to watch all the variables changing in real time and play with the physics through a friendly interface.
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Adding to what Shotglass said about resultant force: AndRand, perhaps you are referring to the magnitude of the force not changing? This is true enough given the context of the discussion, but I think where there might be some confusion between you and Shotglass is that I think he's referring to how Fx and Fy change as a result of trimming to the circle. When tire modelling the magnitude of the force is important of course, but the direction of that force is even more important. I think that's what Shotglass is probably getting at.
I was referring to artificial neural networks. Those are a big set of equations, but the idea is it would learn the existing data set for a single tire rather than groups of many types in order to reproduce it. In the end it's just a neural network. A black box. You don't know how or why the tire works the way that it does, but as long as it reproduces a set of overly complicated test data accurately, you don't care. This is something chassis engineers would be more interested in than tire engineers though, of course.
You can, however, use evolutionary algorithms to come up with constants for other models like Pacejka too though. In fact this is quite commonly done especially with versions of Pacejka MM that have a huge number of parameters to solve for. There was a program called TireGene years back that used genetic algorithms to solve for them given a set of tire data. This is getting a bit off the original point though.
Each neural network setup would be a solution for a single tire. It needs a big set of complete tire data (very expensive to obtain) in order to work. Hence you won't see it in video games any time soon.
Yes, these are the types of papers you should be looking at
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At this point I think you've realized this is not right. One main giveaway that this relationship was wrong were the 0 force valleys strewn across the landscape.
Have you heard of "friction circle theory?" If not, try searching for it.
You've got it
Pacejka's magic model is indeed an empirical model, meaning it has no real physical basis. It's a mathematical fit. However, it turns out to be a very good one and is pretty easily adjustable in terms of getting the initial slope, peak height and location, and drop off after the peak how you want. This is probably why it's so popular. You could use your own equations here too if you wanted. All they're trying to do is fit measured tire data with some equation that will reproduce the data given slip ratio, slip angle, normal/vertical load, and whatever else is desired. All sorts of approaches have been tried successfully to do this and it's an area of constant research. Even artificial neural networks have been done for this. Can you imagine that? Artificial intelligence tire models?
(Granted, for that to work, you need seriously large and complete tire data sets that you won't ever find).So you have a class of tire models like Pacejka's (pronounced "Puh ZHay Ka" by engineers in case anyone's curious) that are strictly empirical curve fit models. The other main class are what people commonly call "physically based" models such as brush models, string models, FEM, and others, that try to calculate the forces directly from various stiffnesses and frictional properties in the tread, perhaps the carcass, and so on.
Exactly! And this is the precise thing that most hobby game developers (and even most of the pros until perhaps just a few years ago) completely miss, myself included from 2000 on for three or four years probably. Even with a book that showed this change staring me right in the face, I didn't connect the dots.
Let's break this stuff down a little more into specific areas:
1) First there is the friction circle/ellipse trimming, which Shotglass illustrated with the red vector. The idea is that even though you may be below the peaks of both lateral/longitudinal force curves independently, you take (making up numbers here) 5 degree slip angle which gives 1000 force, and 0.1 slip ratio which gives 800 force separately from each other. The resultant force becomes (1000*1000 + 800*800)^0.5 = 1280 (^0.5 means to the power of 0.5, or the square root).
If this force goes beyond the friction circle/ellipse, you scale it back so it lands on the circle/ellipse as Shotglass showed. This is the "trimming a friction square to a circle/ellipse" that Bob mentioned.
This works and you actually do get a reasonably decent car to drive, but it's very knife edge and you get the "all or nothing" type of handling that was common in past (and some current) sims. Where you can wind up with a car that's understeer and then suddenly transitions to snap oversteer with little or no warning. Still though, if you make a sim that works this way, you're bound to get a few fans that love it and think it's the most realistic thing ever developed because it's so damn hard to drive it at the limit
Then you can sit back and chuckle at the flame wars about realism that come up in your forum.While this is a good place to start (I'd recommend it for anybody wanting to take a stab at writing their own sim), it is actually quite far off from reality. There is another effect that is completely missed in this approach, which brings us to #2:
2) Imagine another situation where we have combined slip, meaning we have a non-zero slip angle and a non-zero slip ratio at the same time. We're turning and acceleration/braking simultaneously. But imagine that the combined force (force resultant) is small enough that we don't need to trim it to the circle/ellipse. We have something like 2 degree slip angle and 0.05 slip ratio. In point 1, above, we simply look up the force that we get from the "pure slip angle" formula and constants to get the lateral force. Then we look up the same thing on the other formula for longitudinal force. The problem is, neither of these forces are correct any longer!
If we are sitting at 2 degree slip angle and 0 slip ratio, we get the correct lateral force that the magic formula or whatever other empirical formula we use shows, which is only correct for the "pure slip" case, meaning either in pure slip angle or pure slip ratio, but not both in combination. But as we start changing slip ratio, that entire lateral force curve changes! Both curves change, actually. This is what most hobbyists (again, I was guilty of this too) completely miss. The combined slip stuff influences and completely changes both of the curves. In the early 2000's I know for a fact that a lot of the sims that were out on the market also had this very same problem because we were all discussing this subject quite a lot on usenet at the time. I can feel immediately when driving a sim if this is how the tire model works or not. Nowadays most developers seem to have got this worked out, but it was a big problem back then.
This is why if you're using Pacejka's MM or other empirical model, you really need to make sure that you have a version of it that includes the modifications to the curves that account for combined slip behavior. And here lies the fundamental problem that we sim developers run into with empirical models like Pacejka's MM: You have to tune these parameters to make the combined forces work right. If you are a chassis engineer at Ford or something and have tire data where they measured all these combined slip maps and so on, you can tune Pacejka's MM and other empirical models to work just fine and dandy because you've got the real test data to look at.
This is one reason why I abandoned empirical approaches and came up with something physically based. It's not that Pacejka's MM is "bad" at all. It's just that as a sim developer, I don't have a single complete set of data like this for any single tire. Can you imagine poor Scawen trying to tune by complete guesswork something like this for multitudes of different tires all tuned to the bazillions of cars available in LFS? Yikes....
Anyway, I'd still like to encourage you to play with Pacejka's MM more. You'll learn plenty just by continuing with the exercise
Edit: Oh, one more thing. To keep things simple for now I suggest just sticking with a friction circle and keeping the Fx and Fy peaks the same. Once you get your mind wrapped around that then you might try doing the ellipse approach as Tristan rightly stated is a more accurate method. However, the combined stuff in point 2 has a far larger impact on vehicle behavior. Massive. Huge.
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Baby steps... One thing at a time.
Err... What is that for? Modulus of Fx - Fy * sqrt(2)? No wonder the maps are a bit goofy.
If Fx and Fy are equal to or multiples of each other, then F=0. There isn't going to be a non-zero combination of slip angle and slip ratio that results in 0 force of course. See the valleys in the graphs that are at 0 force? That's probably why.You ought to be thinking more along the lines of Pythagoras, probably. I'm curious how and why you came up with that formula though.
If you're trying to make a 3D map of this, all you need to do is map Fx according to its constants and Fy according to its. The 2D vector that you get IS the resultant by definition. No need for doing something extra on top of this. However, as Bob suggested, you then could check the length of this resultant vector and then shorten it so it is no larger than the radius of the friction circle.
Scawen, I think you and I are very much alike
You just summed up my own experience to a "T." Do what you need to do and don't let everybody get you down. Development is hard enough without all the negativity. I feel ya, bro
I get tickled whenever somebody posts one of Ruud's writings from the Racer site. It took a fair bit of arm twisting from me to get Ruud to use Pacejka in the first place back in 2000 or so. If you'll go through Rec.Autos.Simulators at groups.google.com searching for our names around 2000-2004 or so you'll find plenty of detailed discussions on all sorts of things sim development related, including plenty of info where Doug Milliken and quite a few commercial sim developers at that time would pop in and give input.
Ruud saved a lot of those postings at the Racer web site so you might want to check those out. I think there's a fair bit of discussion about combined slip and tire modelling there. I haven't looked in years though so my memory might be playing a trick on me.
Anyway, combined slip is really critical to get right. The first mistake I made was to not treat the lateral and longitudinal force curves as two separate things that influence each other. I started out calculating lateral force from slip angle, then longitudinal from slip ratio, and using them together as a vector sum. Probably something like you're trying to do, maybe? I did that for upwards of four years probably without knowing any better, but just knew something wasn't right...
If you do that (treating it as a sort of friction square with trimming to the limit as Bob suggested) it'll drive fairly well, but you'll get the all too familiar snap spin type of behavior on throttle seen in quite a few sims over the past decade or so, among other problems. However, it's not a bad start at all if you're writing your own tire model and sim. You'll get the effect of the tail sliding out when you hit the throttle, for instance, although it'll feel like it's on a knife edge and overly snappy compared to using other methods.
There were several of us at r.a.s. way back when having a lot of discussions about how to handle even the trimming part. One method I proposed was to let the longitudinal force go to whatever it wanted to go to (as long as it was inside the friction circle), then limit the lateral force to keep you right at the limit, which would change the direction of the force vector. Don't do this though unless you're curious what it's like. It feels awful and makes the car really hard to control (not realistic at all). The other way was to do the "friction square and trim the force vector to the limit" which works a lot better even though that isn't physically correct either. I'm pretty sure most sims worked that way until fairly recently though. Two developers back in those days said that's how they were doing it. No wonder they were "realistic sims" but still too hard to drive at the limit
In reality, adding traction/braking force has a huge impact on the effective cornering stiffness of the tire and the resulting force vector needs to be pointing in the correct direction for high slip conditions. Once this dawned on me and I tried it with a new type of model, every car was transformed into something much better by leaps and bounds. It finally felt right. (Pacejka's Magic Model could probably be made to do this too without too much trouble.) There are more comprehensive versions of Pacejka's Magic Model that do this by effectively changing the parameters depending on both slip ratio and slip angle at the same time. For engineering work where you may have combined tire test data this is as good as you need, but for most of us sim folks you wind up chasing your tail trying to tune things. I'd advise anyone going with a Pacejka Magic Model to make sure they've got a "full version" that deals with combined slip in this way.
Anyway, looking at your graphs I suspect perhaps there's just a math error somewhere. I can't think of a reason why when taking that approach the result would look like that.
The plots are pretty though. What did you use for that? Mathematica?
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Those are bizarre curves. Nothing like reality. Not sure what you did there, but at least the colors are pretty
Saw your post with the pic of that green buggy type thing you built. Impressive
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In LFS this may very well be the case. My first collision system for Virtual RC Racing years ago did the same thing because I treated contact points two ways fundamentally:
1) There was an impact velocity (more precisely, a "normal" velocity perpendicular to the face that was hit) where a big force was applied to get the contacts to move away from each other at the right speed. This included the coefficient of restitution which is just a multiplier to scale down this velocity. This is the energy absorption you mentioned.
2) An additional spring force that scaled with penetration depth so cars could sit on their roofs without slowly sinking into the ground or a wall if you were wall riding. If memory serves me correctly, this part was only done if the impact velocity was below some arbitrarily chosen threshold.
The main problem with this was twofold:
1) The forces were not taken care of simultaneously correctly. I.e., if you have a bunch of contact points, each with its own velocity, then when you add them up the force can easily be too large even if the coefficient of restitution is very small. For instance, in my old system if you dropped a block on a plane with four contact points, it would solve each one independently and you'd wind up with four times as much force as you should really be getting. BOING!! Flying block
Combine this with a fairly low velocity impact (like scraping up against a wall rather gently) where the spring forces come in to play and are added to this, potentially to great effect, and whammo: The car could go flying instead of scraping along the wall. This took all kinds of little checks and hacks for special situations, but was by no means universally good. Good enough 99% of the time if you stay out of trouble and drive properly, but if anybody here has ever played Virtual RC Racing you've undoubtedly seen a car explode across the racetrack now and then after you hit a couple off track objects at the same time at a strange angle or something. This is why
2) The interpentration stuff with the springs where the extra force is determined by penetration depth can happen suddenly in some situations and cause another kick on top of this. My old system worked in a pretty simple way where the car was made up of a bunch of potential contact points (like a flight simulator). It was possible for one of these points to be "behind" a triangle yet just off to the side so it was not literally "touching" it yet. If the car moved just a tiny bit, the collision might register and suddenly there is this really huge penetration and resulting spring force. So a car could be sliding upside down very slowly, then just by chance because of how the triangle geometry was in a certain area with a few objects, you'd get this huge collision that would flip a nearly "at rest" car 20 feet in the air end over end. Very annoying and unfortunately a lot of people don't differentiate this part of physics from the driving model end of things. Suddenly the physics suck and it reflects badly on the rest of the very good model where the really important stuff is (the driving/vehicle model which is separate).
In my case problem 1 was more of the situation. It wasn't so much the interpenetration problem, but rather how I was treating simultaneous contacts.
The solution was rather complicated and took nearly a year to figure out and write and is still not perfect in every way, but suffice it to say I can now stick a car half way into a wall and it will pop out in one time step without going flying even an inch. So there are ways around this. In my case though I had to completely throw out the old collision system and start over. It was not a simple fix by any means. Given that it took a year, I'd be surprised to see Scawen bother. Wouldn't you guys rather have something else instead first
I don't know how LFS works in this area of course. Just sharing my own similar experience. The interpenetration problem you described here is definitely real in some engines and not others. Changing this is a massive task though. Probably was worse than writing the vehicle model itself...
Yes, this is true. This turns out to be the simple coefficient of restitution and is no big deal in practice. You have a target velocity that you're trying to make a certain contact point reach after hitting something and just scaling it down with a single multiplication. (It's just a single line of code in my engine.) In my system at least this was not one of the real problems. I doubt it is in LFS either, but could be wrong.
I'd be surprised to see this ever fixed. If I had to vote I'd say spend the next many many months or a year doing other things rather than rewriting the whole collision response system.
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Posted a two minute long, 50MB movie here:
http://www.performancesimulati ... riplemonitor/MOV02257.MPG
There are eight more in that folder. If you want more links let me know. Also put up a Flight Simulator 2004 clip there I think and a short Crysis Warhead one. The rest is racing stuff.
Here's picture with Crysis Warhead:
http://www.performancesimulati ... riplemonitor/MOV02257.MPG
There are eight more in that folder. If you want more links let me know. Also put up a Flight Simulator 2004 clip there I think and a short Crysis Warhead one. The rest is racing stuff.
Here's picture with Crysis Warhead:
Great. Good luck with it. It's good to see when someone takes on a challenge like this.
After enough hand-waving discussions, at some point the question will have to be asked, "I can imagine it working this way. Now, how exactly will I do this?"
After enough hand-waving discussions, at some point the question will have to be asked, "I can imagine it working this way. Now, how exactly will I do this?"
Android: Yes, that's it.
Shotglass: You're not limited to an empirical model to get friction circles (mine aren't empirical). If you know the friction coefficient and vertical load (max force), you have the radius so can draw the circle. If you have separate longitudinal and lateral friction coefficients you can draw an ellipse just as easily. Depends on how the particular model works, but there's probably a way to work it in almost anywhere. FEM would be more challenging, but nobody's using those in sims.
Shotglass: You're not limited to an empirical model to get friction circles (mine aren't empirical). If you know the friction coefficient and vertical load (max force), you have the radius so can draw the circle. If you have separate longitudinal and lateral friction coefficients you can draw an ellipse just as easily. Depends on how the particular model works, but there's probably a way to work it in almost anywhere. FEM would be more challenging, but nobody's using those in sims.
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