Yo folks!

I wonder in real life, how quickly the force at which the calipers clench the brake disk, varies when the driver changes load on the pedal. Why?

Well now that one can use a 'load cell' to get a true force sensitive brake pedal I wonder if in real life, slight brake pedal force variations, when blipping with your braking foot for instance, have an immediate influence on the actual braking done.

If there would be an ever so slight brake caliper displacement when braking harder and harder, that would mean things like the viscousity of the fluid, the tube diameter, return spring strength, tube expansion etc ALL have some damping effect. Even when the pads don't move, even the brake fluid 'tubes' will expand a VERY VERY tiny bit, which will act as a 'spring' ever so slightly disconnecting the pedal pressure from the caliper pressure..

Could it be however, when I'm braking, heel & toe-ing and have quick, slight, fluctuations of pedal pressure, that the actual braking would react slightly damped and thus show less fluctuation?

illepall

Edit: Bah seems more at home in 'general racing talk'

so what exactly is the question then ?

one thing you certainly dont get with a load cell is the mushiness (very weird word for anybody who speaks german) a brake pedal has despite its pressure sensitivity (ie a real brake pedal moves a bit when you change the pressure)

Well, also, in real life you have power brakes which assist you in depressing the brake pedal from intake-vacuum.

P.S. I'm using lynx right now, i am having problem with fglrx, rofl

Quote from Shotglass :

so what exactly is the question then ?

one thing you certainly dont get with a load cell is the mushiness (very weird word for anybody who speaks german) a brake pedal has despite its pressure sensitivity (ie a real brake pedal moves a bit when you change the pressure)

You can add a strong spring to the load cell system to simulate this as well.

I've wanted to make a 'real' brake pedal for ages, that would do this. All you need is a cheap master cylinder and a caliper, plumb them in, and use a load cell between the pads. Then the flex in the pipes and the hyraulic nature of the system would be taken into account, albeit in a lesser way because of shorter pipes and no flexis.

But I doubt I'll ever get round to it.

Because since its probably a fairly simple spring/damper thing if you simplify it a little, it would be a lot easier for sims to do this for each car.

Of course 2007 won't be the year that everyone uses force sensitive brake pedals, and there are more important things to improve in sims..

I do wonder though if the attatched crap drawing could be the case, or if there are any other factors going on in 'real' (race) car braking that 'flatten' pedal force fluctuations.

I find it nearly impossible in sims to get smooth braking done while blipping the throttle. And looking at video's online from real cars, I just don't believe that their brake pedal force doesn't go up / down a bit when they heel and toe.

Now, there might be some dampening or delay by all the factors you listed, but IMO it would never be significant enough to make a noticeable difference on what happens during heel-toeing.

At the same time I also think that heel-toeing in a real car can be much smoother because of the better pedal placement, and because you merely have to keep the pressure the same, rather than the pedal travel like in most gaming pedal sets.

Quote from tristancliffe :

I've wanted to make a 'real' brake pedal for ages, that would do this. All you need is a cheap master cylinder and a caliper, plumb them in, and use a load cell between the pads. Then the flex in the pipes and the hyraulic nature of the system would be taken into account, albeit in a lesser way because of shorter pipes and no flexis.

the easier way would be to do what frex does and just put a pressure sensor into the pipes

and to make up for the shorter pipes you could always use softer ones

ive also toyed with the ideo of adding a few valves so i have a whole set of different pipes to select from ranging from very soft to steel flex

Quote from Niels Heusinkveld :

I do wonder though if the attatched crap drawing could be the case, or if there are any other factors going on in 'real' (race) car braking that 'flatten' pedal force fluctuations.

unless you get any brakefade and the tubes get really soft you probably wont see any significant smoothing

and keep in mind that race cars use steel flex pipes or similar which dont expand much at all so theres no damping

Quote from AndroidXP :

and because you merely have to keep the pressure the same, rather than the pedal travel like in most gaming pedal sets.

niels is talking about his pressure sensitive (machnical) loadcell system

I know. That's why I put in "most".
I was just saying that heel-toeing consistence is even harder with the normal pedals compared to his load sensitive ones.

i find heel and toe more or less impossible with spring operated brake pedals the only way to do it is by pressing against the hard stop and when you do that you still cant hell n toe with any of logitechs pedal sets due to poor placement of the gas and brake pedal realtive to each other

Just slightly off topic, but the same subject, I wondered the same thing about how throttle implentation works. This was a post I made, got no responses though.

Quote from dontsimon :

Is the kind of throttle inputs we have on sims (value wise, position, mostly linear etc) a good approximation of how a real throttle works?

I've often wondered if maybe some fuzzy logic, or some other smoothing (or an opposite to smoothing) sytem might represent a throttle more accurately?? At the moment is it simply a case of precisely transfering the pot value into a throttle value??

The steering has an analogue smoothing option for pot wheels. Would air intake etc in the throttle always be exact and unwavering?

For years now I've fixed a half an old squash ball under my brake pedals (now on set#3 over about 7 or 8 years) I like the feel of the extra squeeze resistance at the bottom of the pedal's travel, or I'm so used to it now, it makes it feel more realistic but you have to watch the travel when calibrating, ie: Calibrate for pedal travel first then fit your half a squash ball .

The frex pedals are misleading. Unless they changed something very recently, they CLAIM pressure sensitive but it just turns a pot so it is motion sensitive.. I.e. 'pressure insensitive' as motion gets near 0 when you're pressing the rubber..

I guess we could be definitive if there is telemetry of a race car available showing longitudinal G forces and brake pedal force, when braking in a straight line..

Throttle is interesting and I think some sims are weird. I have been told what the problem might be but I can't comprehend. I think throttle should set the 'target RPM' whereas it seems, in ISI perhaps and NKpro for more sure, to be more directly connected to the power / torque. So when you lift off the throttle when the back steps out, you basically don't apply any power as long as the RPM you 'set' with the gas pedal is lower than what the motor is currently running at.

With the 79 mod, in neutral, giving some gas until the revs start.. then even doing this carefully, makes the revs max out! In NKpro, which I have barely played, I found the gas pedal odd in response. As said though I don't fully know how this should behave but I have some suspicions towards a few sims.

Quote from Niels Heusinkveld :

I find it nearly impossible in sims to get smooth braking done while blipping the throttle. And looking at video's online from real cars, I just don't believe that their brake pedal force doesn't go up / down a bit when they heel and toe.

You're 100% correct in that assumption, how much the brakes fluctuate depends greatly on the brake system of the car though (like Shotglass said, tubing is one of the big keys).

Quote from Niels Heusinkveld :

The frex pedals are misleading. Unless they changed something very recently, they CLAIM pressure sensitive but it just turns a pot so it is motion sensitive.. I.e. 'pressure insensitive' as motion gets near 0 when you're pressing the rubber..

theyre currently developing a hydraulic system with a pressure sensor

Interesting question. After giving it some thought I've come to the conclusion that a noticeable amount of force damping in the brake hydraulics is not possible.

I'll try to explain: If you look at a spring and damper as a device with input force and output force then the output force always equals the input force (because of Newton's 3rd law) unless there is also an inertial force resulting from the moving mass of the system. This inertial force is the difference between the input and output force. Now since there are no large moving masses in the braking system and they hardly move anyway, there will never be much difference between the input (pedal) and output (brake) force. To damp the pedal force to a noticeable degree you would need to have more mass movement in the system.

But I think the important question is not how the pedal force relates to the brake pad force but how do the brake pads and tyres respond to the braking force. As we all know tyres, adhesion, friction etc. are still not very well understood so it's hard to make any assumptions but I think it's very probable that both pads and tyres have their very own "braking feel" caused by damping and other effects. I've heard more than once of teams changing their brake pad supplier because of a driver who preferred the feel of a certain brand.

So yes, I think the interaction between pedal force and actual braking force isn't completely straightforward but I don't think the damping is in the brake hydraulics.

Like you said Niels, real data recordings would be the only way to find out. While I do have some experience with data it isn't with a car that required heel and toeing so I can't tell you anything from that.

Thanks JB, good post.. Basically then it is not up to the hardware (pedals) to cause this effect but it should be in the sim, as each car might be different. But we still have no numbers.

I'll gladly believe that I'm just 'crap' at heel & toe but surely not everybody who does it for real can be so crap at it that it hinders their braking?

I have seen some simmers videos where they don't heel & toe but just press both pedals at the same time.. Sure you can keep a constant brake force but its sooooo hard to keep 20kg on the pedal, move or tilt the side / heel of the foot and roll / press the accelerator. That probably gives me at least a 5kg 'wobble'.

Edit: the father of a friend of mine races and I saw he used MOTEC.. G sensors definitely, and perhaps brake system pressure.. I'll ask if he can have a look! Its an old group C car, dunno if he heel & toes but there is a good chance..

id say if you get fluctuations of up to 5kg chances are youre doing something wrong

I call it "not being very good at it" I'm going to invest in something like racing shoes. Socks + 20kg brake force = not comfortable for long periods.

And about the telemetry, even if that is available, the longitudinal G force will also be affected by brake temperature, engine braking etc so when the relationship between pedal pressure and G force isn't 1:1 we'd still not know for sure what causes it.

A little OT question, does anybody know what brake force the G25 pedal has? I just have no reference to "20kg"...