Understanding rear wheels slip influence on steering torque

Discussion in 'General Discussion' started by mantasisg, Dec 30, 2018.

  1. Korva7

    Korva7 Registered

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    I think there is clear difference in how you feel and are able to correct an oversteer between g27 and DD. The difference between my thrustmaster TX (Almost the same as T300) and DD wasn't that big imo. Just more force if you wan't it. And also lower friction in the wheel it self so you need to use damping effects.

    Playing ACC made me wonder if rf2 or acc has more realistic oversteer behavior. There seems to be big difference on the level of grip on high slip percentages/angles (much less grip in acc). At smaller amounts of slip they are closer to each other. And acc with TC at 1 feels similar to rf2 with no TC.

    Now i'm in youtube rabbit hole whatching videos like this.
     
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  2. mantasisg

    mantasisg Registered

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    It is interesting subject, I was also watching Niels Heusinkveld setting up his new DD wheel (also driving Mclaren F1 in AMS) and he was also setting these things. This subject of wheel torque vs rotation speed seems quite interesting. I can't help it, but I usually feel like high caster values feels wrong in simulations, I have T300. I have no problem understanding that higher caster means more mechanical trail leverage, and thus more force on steering, but the shear reaction and speed of the steering in my hands begins to feel strange, as if it starts taking over the actual steering too much. For example even at slightest slip when I would actually like to keep steering straight and adjust rear slip via throttle steering aka giving more or less throttle. But if FFB feels immediate and super eager to self correct then I can't really take an option for picking up light slips with pedal adjustments, but to give FFB a go and don't get into arguments with it, because using brute force to oppose steering into a slide makes no sense.

    Look here at 1:22, thats how classic 911 drives on a limit. Note how he was able to take most of the turn without any significant steering input until the second part off the turn when oversteer angle grew larger and driver had to steer/let steering go into a slide. Note how he was able to keep dragging rear end at an angle with steering mostly straight. As rear was always sliding he could manipulate steering a lot, it didn't seem like steering just wants to self correct badly at this angle, it looked rather light. Driver did do couple small steering into a slide inputs, but also did few steering inputs to the right effectively maintaing high slip angle at the rear. All that while also controling car with throttle, though initially didn't use it because he was braking. If steering would be taking over such driving would be impossible, you couldn't keep dragging slip likethat, because steering would try very hard to correct it as soon as possible. But in footage like this, looks like at this certain interval of rear slip steering self aligning force doesn't mind a little bit of rear slip. It probably goes quite light as there is some yaw moment changing normal attitude of the car, but it probably just doesn't build that force to make it rotate into a slide just yet as it goes through phaze of zeroing before it switches direction.

     
  3. boblevieux

    boblevieux Registered

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    I'm not sure that 911 (RR engine layout) is the best example, as flooring the gas make the front very light.
     
  4. mantasisg

    mantasisg Registered

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    It is good example of the extreme. But principle of steering should be the same for all cars, I think. Self aligning torque should take some time to reverse, definitely shouldn't go 1:1 with the rate of yaw angle increasing IMO. I can't give good explanation why I think it should work like that, perhaps inner resistance of steering mechanism ? Well thats something to think about. Maybe somebody disagree, or has ideas ?
     
  5. The Iron Wolf

    The Iron Wolf Registered

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    I am by no means physics guy, but a lot of hints about vehicle dynamics in rF2 can be extracted via motion and tactile transducers.

    I might be wrong, but above fact to me it suggests 2 things: assuming rF2 simulates physics correctly, you won't feel much in steering column IRL. Second, because both transducers and motion give reasonable hints of rear wheel slip, it suggests that game engine indeed simulates that, it is just not felt via FFB. BTW, one of the biggest differences I noticed with addition of motion to my rig, is that I feel loss of control of the rear way before I feel it in FFB.
     
  6. boblevieux

    boblevieux Registered

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    Grip* and gyroscopic effect are the forces that steers the wheel when the rear drifts, the same forces that keep the steering wheel straight when driving in straight line.
     
  7. mantasisg

    mantasisg Registered

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    That is no doubt true, but its just source forces and doesn't describe how actual system work that has a result of certain self aligning torque that is sent to FFB servo motor. Without certain geometry wheel gyroscopic, tire friction and tire deformation effects would have much less effect, increasing caster increases mechanical trail leverage, so I have no doubt that forces should get increased. But my interest is about the timing of forces, and how does it exactly work when rear end steps out. While of course there is an aligning force, I don't think that when vehicle gains yaw moment as rear end looses lateral friction the self aligning is so ideal that it allows pure perfect direction preserving. I do think it should depend on how sudden and great the yaw moment of oversteer happens to be. I think it this way because front wheels are free to roll back and forward and there has to be certain rigidness/friction in a steering system to overcome initial front wheels self aligning at the very first moment of rear end stepping out. Some of which will of course be drivers hands and the force that he puts in, but even if driver keeps his hands as lightly as possible on the steering to be able to feel finest possible self aligning torque changes, the fronts self aligning when oversteering shouldn't be ideal even with huge caster, especially when car overturning yaw moment is big and fast IMO. P.S. I don't have much trouble with all that in rF2 as in AC for example, but greater caster values makes me wonder too.
     

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