Understanding rear wheels slip influence on steering torque

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

  1. mantasisg

    mantasisg Registered

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    Do you ever wonder about mechanics which makes steering wheel give output for oversteering vehicle ? It is still quite a mystery for me. I don't understand it well.

    I often wonder how precisely and how immediate steering torque should be suggesting that car is overturning/oversteering and how much of it should be guess steering. How it works ? Should there be some compromise in simulation ? How does simulation software solve it ?

    Obviously it is very complex phenomenon, as car can oversteer in many different ways. I suppose it depends a lot whats the state of grip balance F/R, and whats the SAT and steering input at the very moment that bad overturning begins.

    For example, I suppose, overturning will give much more suggestion through steering wheel if front tires will have much less slip angle, comparing to rear. And it would be much harder to tell whats going on in case of neutral steer (when front and rear tires has same slip angle) and many things can happen such as all tires can run too big slip at the same time, or fronts can regain grip and create sudden steer quickly increasing rear slip even more... Am I thinking in right direction ?

    Along with output. Steering input is very important too, as oversteer occuring while increasing steer angle it should be harder to tell if turning radius is decreasing due to steering input, or because of overturning phenomenon.

    Is there any data on how oversteer affects SAT ?
     
  2. Louis

    Louis Registered

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    I think without canned effects or "less than real physics" we wouldn´t be able to catch an oversteering relying only in visuals and steering wheel ffb. I believe in real life with superfast,rwd cars when you felt through your steering wheel that you are loosing your end is already too late to catch the slide.
    If we all had 6dof sim motion rigs, we wouldn´t care much about steering wheel ffb

    *if i understand correctly your post
     
  3. RaceNut

    RaceNut Registered

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    I'm not sure I'd agree with that. I actually find that there is something of a disconnect when the various streams of FFB don't support one another. Just as we have less information without motion, we also have less with motion but, without the corresponding wheel-FFB. You may be surprised by how our brains cue into very subtle effects. Some effects may not be realized fully until they are missing and suddenly, it can feel unnatural to us.

    It's a bit like musical instruments playing different songs at the same, it's just noise but; when working together in harmony, it becomes something truly amazing by comparison.
     
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  4. Louis

    Louis Registered

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    "wouldn´t care much" not "wouldn´t care at all" :D
    To me, real Racing is about 99%* g forces effects on the body and visuals. 1%* steering wheel ffb. Sim Racing is 50%* steering wheel ffb and 50%* visuals
    *made up numbers to make the argument
    back to topic...
     
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  5. Andregee

    Andregee Registered

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    The effect that the steering wheel produces when oversteering a counter-steering impulse is absolutely real.
    The whole thing is based on the self-aligning torque. A wheel is always anxious to align itself in its direction of motion. As soon as the rear of a vehicle breaks out, the direction of travel changes and the front wheels no longer point in the rolling direction, which is why the self-aligning torque starts until the rolling direction and steering angle match. And that is the force, that you can feel in the steering wheel.
     
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  6. misi

    misi Registered

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    As far as I raced (100cc and 125cc shifter Karts) I totally agree.
    They used to say to me: "A kart is mainly driven with the sensation coming from your ass".
     
    Last edited: Dec 30, 2018
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  7. mantasisg

    mantasisg Registered

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    I agree with g-forces argument, however I'd argue that it is very dynamic and depends a lot on relative changes of g-force. You can definitely judge the motion of g-forces, but you have to able to react to them at first. For kartings g-forces makes a lot of sense to be massively important, as kartings drive in tight tracks and slower speeds, also the vehicle is very short and that is important too. I think like that because you have same same g-force switch as car breaks out of its supposed trajectory at low-g curve, as in high-g curve, and definitely you'll feel better the change in low-g situation.

    I don't really get the logic of motion rigs, I think they are little practical. I think it would be possible to make some systems which would provide constant perception of pull/push in various directions, but I don't want to share ideas on that :D

    Visual cues are surely underrated. It is most important information for a pilot of any type of vehicle. To be more precise - peripheral vision. I have read that human reaction to proprioception cues is fastest, reaction to sound is faster too, but it has to be obvious enough in the first place so in terms of perceiving switch in acceleration it has to be obvious enough.

    Last, but not least. If G-force gets saturated into FFB physics, there is no way that it would not mask out pure feel and wouldn't affect your work as a driver. It might be more realistic in terms of level of awareness, but it would distort actual dynamics of steering.
     
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  8. Stefan_L_01

    Stefan_L_01 Registered

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    If a normal steering that turns a car produces a force on the Wheel, I´d say it´s logic that if the same turn momentum for the car is brought up by a spin that the front Wheels have less work to do (in Terms of directional change) and thus forces on the Wheel get lower or even negative.
    The interesting question is: What if you build a Suspension where for turning the forces on the Wheel are 0 (ideal case), at the edge of overbalance. Would you feel something now in a spin? I´d say no
     
  9. mantasisg

    mantasisg Registered

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    Of course it is real. But is it that simple ? For example if you are turning right in heavy G curve, you feel that wheel wants to turn left, if you'll oversteer it will still want to rotate to left, and you'll have to be able to distinguish quickly that car is oversteering and allow the steering wheel to spin freely so you'd maintain good slip angle at front, and keep the car in steerable condition. The question is how well and easily you'll understand that you have to let wheel spin, before you'll catch it and start countersteering. The moment when you have to catch steering wheel and start countersteering is probably even more interesting subject. We all do it, and some are very good at it.
     
  10. Andregee

    Andregee Registered

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    He can do it

     
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  11. mesfigas

    mesfigas Registered

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    blast from the past that BMW :)
     
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  12. d0nd33

    d0nd33 Registered

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  13. Korva7

    Korva7 Registered

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    Just drove the gt3 porche and tested this. When i'm in corner turning with maximum force -> SAT is at it's maximum or close to it. If the oversteer starts in that situation, i don't feel the oversteer at the wheel. Just because of the visuals i start to countersteer, and then ffb tells how much to turn the wheel.
     
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  14. mantasisg

    mantasisg Registered

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    I am actually surprised how it is difficult to understand something that we do so much, and something that gets ever natural for us. I am so confused.

    It makes sense that car overturning would produce torque on steering axis that works in different direction, and would produce reduction in normal steering torque for brief moment when the car is in pendulum motion. Still unclear though. But you are probably right.

    I think I have missed that point where steering wheel gets light, because it has to start spinning to opposite direction, I wonder if that is not an illusion. I really don't get if the steering wheel should actually get lighter the moment that tail steps out. Also do the forces actually get negative ? Wouldn't that mean that steering wheel would start to spin in different direction ?

    I wonder if it is even possible to get such suspension/wheel/geometry which would give no force at all at the edge of grip, it would be interesting to drive a car with steel disks instead of rubber tires, so it would have no pneumatic trail and have little friction, it would probably still give tiny bit of aligning torque because of friction. Would be interesting to try with different caster, mechanical trail.
     
  15. mantasisg

    mantasisg Registered

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    Thats entirely different thing of what I am thinking about, though it is good to observe for the catching and countersteering, but oversteer itself is not only predicted, but caused on purpose there.

    What I am thinking about is situations like this, where overturning happens by surprise, and fast. And it does happen in racing, and with modern tires which aren't designed to run big angles, and they drop fast as you see there, look how much steering corrections he does (by the way the driver is alien):


    Thank you, going to spend some time with this, seems interesting.
     
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  16. Louis

    Louis Registered

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    I think he react before a certain g force occurred
     
  17. Alex72

    Alex72 Registered

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    Looks like he got the tire down in the "ditch" which forced the car left and then experience kicks in to counter it and save the situation. Its all in the backbone (experience). Dont ask me for more technical explanation than that. :D
     
  18. GTClub_wajdi

    GTClub_wajdi Registered

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    Exactly. In real life you feel the car behaviors with your vestibular senses and you feel it before the steering wheel, the steering wheel in real life is used to correct the car behaviors( oversteer/ understeer....). So I’m real life you have that tenth of the second of time that give you the posssibilty to correct the car action and you do that with your steering wheel and throttle/ brake pedals.... in sim racing you feel the car behaviors and you correct it through the steering wheel in the same time and you almost don’t have any time to correct it..... so in real life it is more easy to catch the car.... you have more time to react....
     
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  19. mantasisg

    mantasisg Registered

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    Yeah there is quite a ditch on the inside apex there. I wish to port this track to rF2.

    The driver is actually racing for real for first time, he actually won a simracing competition few months before that race, and that way he won a place in a race team. Interesting stuff.. the car later lost brakes, for the other driver, and he did crazy save by doing a shift lock and spinning on purpose.

    You can compensate this lack of info in a sim by using exaggerated yaw camera motion. Real life still might give more cues in some situations, but steering work is more demanding if steering torque output matches needed input less.
     
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  20. Nitrometh

    Nitrometh Registered

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    Freude am Fahren :D
     
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