1. Do you need support for Assetto Corsa Competizione? Please use the proper forum below and ALWAYS zip and attach the WHOLE "Logs" folder in your c:\users\*youruser*\AppData\Local\AC2\Saved. The "AppData" folder is hidden by default, check "Hidden items" in your Windows view properties. If you report a crash, ALWAYS zip and attach the WHOLE "Crashes" folder in the same directory. Do not post "I have the same issue" in an existing thread with a game crash, always open your own thread. Do not PM developers and staff members for personal troubleshooting and support.
  2. As part of our continuous maintenance and improvements to Assetto Corsa Competizione we will be releasing small updates on a regular basis during the esports season which might not go through the usual announcement process detailing the changes until a later version update where these changes will be listed retrospectively.
  3. If ACC doesn't start with an error or the executable is missing, please add your entire Steam directory to the exceptions in your antivirus software, run a Steam integrity check or reinstall the game altogether. Make sure you add the User/Documents/Assetto Corsa Competizione folder to your antivirus/Defender exceptions and exclude it from any file sharing app (GDrive, OneDrive or Dropbox)! The Corsair iCue software is also known to conflict with Input Device initialization, if the game does not start up and you have such devices, please try disabling the iCue software and try again. [file:unknown] [line: 95] secure crt: invalid error is a sign of antivirus interference, while [Pak chunk signing mismatch on chunk] indicates a corrupted installation that requires game file verification.
  4. When reporting an issue with saved games, please always zip and attach your entire User/Documents/Assetto Corsa Competizione/Savegame folder, along with the logs and the crash folder (when reporting related to a crash).

Physics differences AC/ACC

Discussion in 'ACC General Discussions' started by chargingcar, Feb 21, 2018.

  1. Plus really strange steering geometries.

    I once did an hour stint with a rental kart and barely managed to lift a drinking bottle in the pit. It was fun but man, I had no idea how heavy it could be. :)
     
  2. mantasisg 2

    mantasisg 2 Alien

    I hoped that this thread will be about physics, but all you rant about are FFB stuff. Obviously it overlaps physics, but the talk still is not really about physics :(




    :(
     
    stefanoCasillo likes this.
  3. Torcano

    Torcano Alien

    Sorry to disappoint but most of what you are gonna get from these ACC threads is a bunch of "speculate and/or over-react", hard to stick to topics in such an environment. I'm just gonna wait till early access and keep an eye on dev comments in the meantime, the rest is just unadulterated white noise for all I care. :D
     
  4. Andrew_WOT

    Andrew_WOT Alien

    Doesn't any discussion end up with FFB? :)
     
  5. elchshooter

    elchshooter Hardcore Simmer

    Of course.
    No good FFB without good Physics.
    And the best physics are quite useless if the FFB can't transport it's qualities to the driver...
     
  6. mantasisg 2

    mantasisg 2 Alien

    Tell that to those who are using gaming analog controllers :) They are still somehow having same physics, AFAIK.
     
  7. elchshooter

    elchshooter Hardcore Simmer

    True, but that's like eating lobster with ketchup. Still nice, but you know... ;)
     
  8. mantasisg 2

    mantasisg 2 Alien

    The point was that even with no FFB at all, physics are still there.
     
    stefanoCasillo likes this.
  9. elchshooter

    elchshooter Hardcore Simmer

    That's the case with most things :D
    I did get the point.
    My point was that ffb is an immersive way to experience good physics, in my eyes, much better than just to see it. This, and the fact, that ac just feels natural compared to other sims is the reason why the physics talk always seem to end in an ffb conversation.
    I, as a customer, can't judge if the math is correct. I can only state that it feels right for me.
     
  10. Had a 2h kart race with no rev limiter together with a friend many years ago. The track had small twisty and some wider fast turns with a lot of grip. At the beginning we switched at ~20 min, at the end we had to do this every 8-10 min. I was that much worn out, I really almost loose the car in a fast turn at ~ 70 km/h because my arms has gotten quite lame. Any comparison Simracing/Real Racing is just silly...

    I will do a F4 training with 20 laps at the Red Bull Ring (short layout) in May and if this thread is still there I will post my experience ;-)
     
  11. Using the car as the reference frame (and therefore including fake forces) makes things more confusing...

    Blue arrow by the tire should be pointing straight down, green arrow should be pointing the other way, and the horizontal pink and blue arrows should not be there. Instead you should have an arrow pointing down from the car's CoG in addition to normal force (at tires) and centripetal force (friction - opposite of green arrow). A car rolling over is about sum of torques, not forces. The car will start to roll when the torque caused by the outside tires is greater than the opposing torque caused by gravity.
     
    GRFOCO likes this.
  12. mantasisg 2

    mantasisg 2 Alien

    Yes I didn't show car weight force, and tire reaction normal force... Maybe I should have, though I only wanted to show forces that roll the car, CoG and tire normal force is obvious anyway. Why blue arrow by the tire should be going straight down ? It is actually the same force as horizontal blue arrow, which is the torque of the car chassis caused by some strong bump on the inside tires. @mclarenf1papa. Well at least I think it is like that, might be wrong, and you right.

    So the car goes in a lowish radius curve fast, hits massive bump, lets say tall kerb.

    The green arrow is really the force of tire slipping out, in case if it can't fully support the lateral force anymore. And my idea was that car rolls around its CoG at first from strong enough force impulse (maybe very hard hit to the kerb). Centrifugal force (well the inertia actually which pulls out of the curve) pulls whole car out, but because whole chassis is also in a rotation around its CoG inside side gets pulled out faster than outside side. The bump from kerb force must be greater to overcome opposing moment caused by CoG, which should be easier because if car is in a curve there is also a centrifugal effect which adds up to the roll. As the car keeps rolling CoG opposing moment, or torque should become lesser, as leverage - distance to outside wheels will become shorter, also CoG will get higher, and it will just pull car over if it will stay in a curve. Unless increasing tire normal force would compensate... Might be wrong IDK, it is a very complex situation.

    CoG moves towards outside wheels, which will increase normal force on them, should also help with traction, even if it is the very edge of sidewall/thread, no ?

    I also think wouldn't there be three phases or something like that ? First phase - car rolls around its suspension geometrical roll center like it always does in curves. Second phase, car hits very massive bump, suspension can't cope and pivot point for brief moment changes to CoG point of car. Third phase, if the CoG moves out and up too much in combination with curve radius and speed then pivoting point changes to contact patch of outside tire, if it has the grip. Third phase can be skipped if the impulse of bump is insane or whole car jumps high so it rolls over in air. I think.
     
  13. Rudski

    Rudski Alien

    I'm certainly no expert but that sounds wrong to me, wouldn't it be more related to the speed, angle, height of the car, weight of the car and possibly the size of the wheelbase? Strictly speaking I don't think this statement is accurate, I don't think a car rolls simply because of forces on the tyre.
     
  14. mantasisg 2

    mantasisg 2 Alien

    I think that when car is on two wheels, then the outside tires normal force, and car weight force down from CoG forms a pair of equal forces which forms one torque moment force, which fights other forces which try to roll the car over. I am not sure, should try to calculate, but I guess this torque gets smaller as the horizontal projection between outside tire and CoG becomes shorter as car rolls.
     
  15. BBernes

    BBernes Racer

    Just remember to measure the wheel rotation from lock to lock and set it with soft stops on each car. That way no one needs to make a list of the wheel rotation and set it manually every time they change cars.

    That is a hassle in AC.
     
  16. Centrifugal forces aren't real forces, so using them complicates understanding the physics correctly.

    The torques produced by the normal force and gravitational force actually go in the same direction (in your drawing, clockwise) - they don't cancel each other out as you've stated. So what you can then do is use the center of gravity as your radius/pivot point - gravity's torque then goes to zero (fN=Fg in a steady state scenario. I used that for simplicity but the problem still works out if you pick another radius). Doing this, you're left with the frictional force of the tires (pointing to the right) and the normal force at the tires (pointing up). Up to a certain point, the torque caused by fN will be greater than the torque caused by the frictional force, so the car will fall back down onto its wheels. If the force of friction is large enough or the angle of the car is high enough already (therefore fN's torque is smaller), the net torque will cause angular acceleration and the car will roll. In the video, this is helped by the impulse of the collision with the curb (it has some additional angular momentum because of it).

    Once you start talking about rotational motion in physics, everything becomes less intuitive, but it's not wrong. It has to do with the CoG height, track width, frictional force of the tires, weight of the car, and any additional angular momentum added to the system. If you look at it in a 2D plane like this, it's a high school or first year of college/university problem; nothing too complex.
     
  17. mantasisg 2

    mantasisg 2 Alien

    @mclarenf1papa yes I can understand and I agree, I think. Just want to point out again that both blue arrows in my sketchy scheme are representing torque caused by external forces rolling the car (for example hard impact with a kerb in a turn), it is not tire normal reaction force, those are missing in my scheme.

    True about centrifugal force that it is not really a force but illusion as inertia patch matches velocity vector, and it just seems that foce is dragging straight away from the center. Still confusing though. It is still somehow a load IDK, even though it is just an inertia.

    Having in mind that thread is ACC vs AC physics, and ACC will have only GT3 cars, which just wouldn't roll over, this discussion is probably pointless. But even if car wouldn't roll over perhaps those principles still are very important for kerbs surfing.
     
  18. LChaves

    LChaves Hardcore Simmer

    Car on track physics should use Kunos own system of course.
    However, damage, destruction and deformation physics... i don't think the UE4 system would hurt (or some middleware).

    I wonder if it's possible to use just parts of it.
     
    BrunUK likes this.
  19. Kade

    Kade Hardcore Simmer

    @mantasisg 2 Your initial thought was correct. The car has angular velocity around some point (not necessarily CG or tyre contact patch) from the impact it had earlier so this problem is not solvable by using statics. It's a dynamics problem where you need to take the sum of torques like @mclarenf1papa suggested and see if the angular deceleration is enough to stop the angular velocity before the car reaches rollover point (that would be tyre normal force reaching right side of the CG in your free-body-diagram). Your free-body-diagram is wrong, you cannot add angular velocity as a new force because it isn't one. It's not solvable by using only statics and that's where you go wrong. Note that you could have a situation where car is shown at completely level state but still have enough angular velocity to roll over..

    Also what happens in tyre at that state is completely out of tyre model's area because tyre is not gripping with it's original "contact patch" at all anymore. What happens is complex as f when tyre sidewall starts to deform under the weight of the car in that angle. Even the grip efficient can MOMENTARILY reach values higher than it would with any normal "gripping" situation if the tyre stance was in it's natural state. This is partly the reason why rally cars would be slow on gravel with "grippy track slicks". It's completely different world of physics when you're using tyre sidewall to generate lateral forces in the car. AC's empirical tyre model obviously is not designed to reproduce correct forces in situation like that and how could it be? Where do you get data for such things? I don't believe rFactor2 or iRacing "physically-based" tyre models work even close to real life in those situations..
     
    mantasisg 2 likes this.
  20. Stereo

    Stereo Alien

    Not to mention the contact patch moves in weird ways, whereas physically AC's just using a single point in the center of the tire regardless.

    One interesting aspect of that mini rolling over is that it jumps; with less load, tires act more effectively (some weird rubber reason). So even though it's only on the edge of the tire, it can get a lot closer to the peak friction, so the overall tire force is even more horizontal and helps it roll.

    [​IMG]
    Easier to explain with a diagram; even though the lower arrow is a smaller lateral force, it's a pretty high 2.0 friction coefficient, passing under the CG and can roll the car. The upper one's more like a 1.0 friction coefficient and keeps the car on 4 wheels.
     
    mms and mantasisg 2 like this.
Similar Threads
Forum Title Date
Physics modding - Cars & Tyres Suspension editor & physics/graphic differences Oct 30, 2017
Chit Chat Room Gt car lap time/physics differences Feb 13, 2015
Physics modding - Cars & Tyres Tyre Physics settings ( PIRELLI 265/645-18 DH, DHB, WH ) Jun 29, 2023
ACC Physics New physics didn't work for the BMW M4 GT3 May 2, 2023
ACC User Interface Simulation is not only the physics!!! Apr 20, 2023
ACC Blog The ACC V1.9.0 physics notes document Apr 19, 2023
Physics modding - Cars & Tyres Tyres physics, need some explanations on FZ's, Dx_REF,LS_EXP's and MULT Jan 19, 2023
Programming Language - Apps - GUI Themes Small excel tool to edit car physics Jan 15, 2023
Programming Language - Apps - GUI Themes Is it possible to change physics values in game with Python? Sep 12, 2022
ACC Troubleshooting Crashes in MP endurance race UE4 & Physics (12h) Mar 12, 2022
ACC Physics ABS problem ? Physics ? What happened here ? Dec 7, 2021
ACC Troubleshooting Сar does not move [Duplicate report from Physics] Dec 1, 2021
ACC Controls & Peripherals 400hz physics refresh rate. Nov 24, 2021
Physics Bugs & Issues Physics issue with road cars in AC 1.16.X Oct 29, 2021
Physics modding - Cars & Tyres Realistic physics? Aug 29, 2021

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice