Oh gravity?

Discussion in 'General Discussion' started by sharjeelr, Jun 20, 2018.

  1. sharjeelr

    sharjeelr Registered

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    I have had this nag in the back of my mind for years but partly for the reason of being lazy and partly to avoid throwing a molotov cocktail into an already divided sim racing community I never bothered to get it clarified. But I can't stand this itch anymore so here goes: has no one ever noticed that if you park your car (any car) in neutral on an incline (uphill or downhill slope; eg Eau Rouge) in Assetto Corsa, the car stays stationary and does not roll backwards (in this case) at all? Similar anomalous behaviour is seen when the car should actually be rolling forwards downhill as per the commonly accepted norms of gravity by matter on macroscopic scales. To be honest, i noticed this about 2 years ago, not sure if this is still there. Why am I asking in an unrelated forum? Should that matter, it's just a general question about car physics. So if someone could please answer this, I could finally get rid of one of my peeves. Thanks.
     
  2. SPASKIS

    SPASKIS Registered

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    In rF2 a car in neutral gear will go down slope. Sometimes it happens in the grid where you need to press the brake until the light goes green to prevent a jump start.
     
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  3. ADSTA

    ADSTA Registered

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    Because AC! :p

    edit:
    In the rF2 player.JSON:
    "Hold Brakes#":"When you enter the vehicle, hold brakes until it is shifted out of neutral"

    But that has nothing to do with OP comment as he has already moved.
     
  4. Daniele Vidimari

    Daniele Vidimari Registered

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    That's curious, i'm gonna try it!

    edit
    True, it's like there is a automatic handbrake, if you put the 1st gear and tap a little bit the throttle, after you reach 3km/h the car start to go down slope.
    I also find odd the lack of FFB while standing still.

    edit 2
    Just discovered that in rF2 you can turn on the engine by going downhill.
     
    Last edited: Jun 20, 2018
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  5. stonec

    stonec Member

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    The Pacejka tire model which AC is based on (I know someone will probably refute this) cannot deal with zeros in the denominator, which is essentially what happens when your car stands still. The whole physics model breaks down at very slow speed so they have to use some alternative method of calculating low-speed velocity changes. rF2 is based on physical first-principles tire model and I haven't seen any low-speed issues with it since day one.
     
  6. sharjeelr

    sharjeelr Registered

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    Hope I did't cause confusion. The cars behave perfectly fine on inclines in rf2 i.e., that is roll downhill in neutral. I have noticed the anomaly of cars staying stationary in neutral on inclines only in AC; well to be fair I haven't tested in any other sims.
     
  7. sharjeelr

    sharjeelr Registered

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    Interesting. Do you mean "the cars start" while staying in neutral or you have to clutch and engage as you would in real life for starting cars having completely discharged batteries?
     
  8. Daniele Vidimari

    Daniele Vidimari Registered

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    As in real life! You need to map the "ignition" button to turn off the engine and then press it again when you are ready to start going downhill.
     
  9. Nielsen

    Nielsen Registered

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    I dont own AC but it sounds pretty lousy.
    Lousy because a very simple racing sim like Raceroom is able to simulate this self-rolling if the track goes up or down.
    But if rF2 is able to start the engine by letting it roll downhill then Im a bit impressed :)
    ByTheWay: Is it possible to get the engine started rolling backwards if you select rear?
     
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  10. peterchen

    peterchen Registered

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    Should have nothing to do with tyre-model.
    rF1 had a similar technique and there it works also correct! And as Nielsen said, R3E does it too.

    However, i´ve noticed it in an old vid from AC early days, confirmed it for myself when AC was gifted to me and it was one reason why I don´t use AC. It´s just one proof that AC´s physics engine is lousy and has nothing under the hood.
    By the way: AC runs perfectly normal with a Phenom II X4 @ 800 MHZ! (besides some fps-loss) That says it all. Try that with rF2.......
     
  11. Daniele Vidimari

    Daniele Vidimari Registered

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    Yes, tried just now!
     
  12. kiko0602

    kiko0602 Registered

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    yes it is!
    people are used to use automatic clutch so they missed this thing im sure..
    like manual starting engine...
    and it think that was possible in rf1 to..and if i remember correctly you could do it in netkar pro and few other sims
     
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  13. Ville-Samuli Mutanen

    Ville-Samuli Mutanen Registered

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    Cars were rolling naturally at some point but was disabled later to stop cars rolling on the pitlane if I remember correctly. Physics below 3km/h doesn't have much priority in AC.
     
  14. Nielsen

    Nielsen Registered

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    If that is the reason then I shouldnt have used "lousy" about AC :)
    Because if the reason is some kind of official hack because users wasnt able to hold the brake on the grid then its these users thats "lousy".
    Because in RL even a rookie driver will be able to keep the car steady(hold brakes) on the grid. :D
     
  15. Filip

    Filip Registered

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    It is related to tire model.
     
  16. David Wright

    David Wright Registered

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    Well you did say someone would refute it - so I'll refute it. AC uses a brush tyre model. Of course its quite possible/probable that a brush tyre model also struggles with zero speed.
     
  17. SPASKIS

    SPASKIS Registered

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    I disagree on this since I have observed some speed related issues. Let me remember which was the case and I will post back.
     
  18. Lazza

    Lazza Registered

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    10 years ago I had to use this feature (albeit uphill, into the final chicane at Spa to be exact) in rF1, after managing to switch off my engine on a formation lap. I'm still happy I thought to roll start the engine, because I've had complete brain failures in other scenarios around the start of races...

    Anyway, having a car not roll on a slope despite not being in gear is a design choice I would say. I can't see how it's related to tyres unless the game stops you moving below a particular speed at any time, which seems unlikely.

    What I haven't checked in rF2 (or, recently enough to remember) is a change in rolling speed when shifting gears, with the clutch in. I seem to remember that happening in rF1.
     
  19. Daniele Vidimari

    Daniele Vidimari Registered

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    I think @stonec was referring mostly to the lack of FFB when the car stands still, and indeed seems to be all correlated, like if the physics (or tires?) is turned off when speed < few km/h.
     
  20. Lazza

    Lazza Registered

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    @krusti No, I don't think his post was specific to FFB, in fact nothing about FFB was mentioned. But my post wasn't directed at one person, either.
     

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