Sim Brake Thoughts

[pilmat]

I've been playing with a lot of different brake ideas recently. First off, my own rig is G27 pedals with a GTEye spring in the brakes. The two rigs at work are Fanatec CSR-Elite pedal equipped. A good friend has a full CSR-Elite set-up, pedals and wheel. And I just installed a customer rig with stock G27 pedals (the GTEye spring is in transit).

While in a long session at my friend's, on his CSR-E's, he made an interesting comment. He said that the pedal is very "position sensitive". Elaborating, he meant that the brakes lock up at a certain brake position regardless of anything else (like speed). Being the engineer I am, I had to think of a reason why that was true/false. Then it hit me: all brake systems in sims are position sensitive!

How? Easy, look at what the sim sees from your pedals. It only sees voltage. Whether that voltage is from a potentiometer (pot) or a load cell (some form of strain gauge) or hydraulic pressure sensor (another form of strain gage), the input to the sim through our trusty USB ports is a voltage, or more specifically, a quantity of brake applied which is a number of digital steps. This is a percentage of brake application.

What is the pot measuring? The amount you have compressed a spring.
What is a load cell measuring, the amount you have deflected a piece of metal (a very stiff spring).
What is the hydraulic pressure sensor measuring? The deflection of a metal plate that has a strain gauge attached (another stiff spring).
All 3 provide an output voltage to our controllers that is digitized and then given to the computer as a position (# of steps).

My point is that all 3 systems are virtually the same*. Each with a learning curve, but all three require you to move your foot to a certain position to get the desired braking performance, not at all like a real car. The issue is that the controllers do output things like pedal velocity or force, so the sim can only process what it was given.

We are going to have to change our hardware and then have a sim written to take advantage of the new hardware. Until then, you're going to have a hard time convincing me anything more than G27 pedals are required for a "fully immersive experience"!

Oh, and with all the above set-ups, stock/aftermarket spring and load-cell, I turned the fastest lap in the stock G27! It took me a good bit to go faster on my own rig

* I haven't tried a hydraulic system yet. I'm having trouble convincing myself that $300 is going to make any real difference. I'm open to thought though!

 

[mrbasher]

Exactly! There are only two differences between a the different kinds of brakes. The feel and the stiffness. That is IT. (in my opinion) I have done extensive testing in developing a brake pedal of my own using different sensors, etc. and I have come to the same conclusion.

You hit the nail on the head.

What makes braking more consistent seems to be more stiffness, within reason. As near as I can tell, this is because of the following:

Most pot based pedals have relatively weak springs, this is because the pedal is made to move a fair amount of distance in order to achieve full voltage swing on the pot. (Even though one maker in particular doesn't bother taking advantage of the full travel. It's not Logitech, their pedals are geared to use the entire available range) With this in mind...

Let's say an example pot based pedal requires 20 pounds of force to achieve 100% braking. So 10 pounds of force would be 50% braking. How well do you think you can modulate that 10 pound difference between 0 and 50% or 50% and 100%? The answer is, not very well because you just can't easily feel this with your feet.

Now, increase this to 100 pounds of force for 100% braking. This seems to be a very reasonable level believe it or not. This means it takes 50 pounds of force to achieve 50% braking. Trust me on this, you can immediately tell exactly where the pedal is with your foot based purely on how hard you are pressing the pedal.

Adding stiffness to the braking immediately changes the position based braking to pressure based braking, with regard to feel. It's still position based, but your brain doesn't see it that way any longer.

I am right in the middle of developing a brake that accomplishes exactly this, using no load cell and achieving full resolution due to using the entire available voltage swing.

Anyhow, I'm glad someone else noticed the same thing!

 

[Mahnegold]

That's exactly how the "realistic brake mod" of the T500 works. Even if it cuts a bit of the pedal travel. The additional resistance makes it to work better. Good enough for me, to switch between T500 pedals and CSP without a problem. And without considering the T500 pedals as a big disadvantage compared to the CSP.

That's just my 2 cents on this ;-)

 

[Ripster]

I agree with everything said here... but it is much easier to measure pressure applied vs pedal travel. So no matter how stiff a spring you put into a pots type pedal it will always be easier with a load cell. At least with a two stage spring you can tell where the braking starts.

 

[mrbasher]

I agree with everything said here... but it is much easier to measure pressure applied vs pedal travel. So no matter how stiff a spring you put into a pots type pedal it will always be easier with a load cell. At least with a two stage spring you can tell where the braking starts.

No offense, but I don't think you fully read what was said... Even with a load cell, it's measuring pedal travel. The only difference is the stiffness and how far the pedal moves.

 

[Ripster]

No offense, but I don't think you fully read what was said... Even with a load cell, it's measuring pedal travel. The only difference is the stiffness and how far the pedal moves.

I agree that even with a load cell it is about pedal travel (as minute as it would be) and I agree it is about distance traveled. But in essence a load cell is more about pressure applied than distance traveled, for most of us humans we can regulate pressure much better than measuring how far we moved a pedal.

Though I guess if you wanted to you could also argue it is about pressure applied as well. Pressure x Spring tension giving you distance traveled. So pick any variable you would like.

 

[mrbasher]

I have a feeling this will end up being a bit of a debate. People have been told for the last few years that pressure is better than travel. IT IS... However, a load cell or something to measure that pressure isn't the answer. The reason load cells have gained such traction is mostly due to marketing. However, the concepts used are identical to a pot based pedal.

I'm going to try to explain further, even though Pilmat already did a fine job of it...

It is true, a load cell measures pressure. They're useful for this purpose because they are the spring and the measuring device. However, their output is based on a resistance change along the surface of the load cell. As it bends, this resistance changes and thus does its voltage output.

Furthermore, on it's own, the load cell used in the Fanatec pedals forms a circuit that looks like this:

(positive)---resistance---(output)---resistance---(negative)

This is a voltage divider. As the load cell bends, both resistances above change inversely. The change however is quite small and requires amplification. It's also not linear and requires a special type of amplifier in order to operate properly.

Guess what a pot looks like...

(positive)---resistance---(output)---resistance---(negative)

Yes, exactly the same, a voltage divider. As the pot rotates, the resistances change, outputing a varying voltage. The main difference here is that the pot moves much further and with basically zero resistance when compared to a load cell.

So, both work the same way, both measure a change in DISTANCE. If you still don't believe me, what do you suppose would happen if the load cell were not allowed to bend at all? What if you put 100 pounds on it? Nothing would happen, it would not measure anything.

Now that we have that out of the way. I'm going to revisit what I said earlier and explain further.

The reason the Fanatec load cell pedals allow the pedal to move some distance and seem progressive is that they have two stages. Stage 1 is the foam inside the pedal compressing. The takes up approximately 50% of travel and during this time the board in the pedals has a higher sensitivity because the load cell is not bending much. It is however BENDING, it has to or it's output would not change. The second half of travel, the foam piece is mostly compressed and you are operating primarily on the load cell itself. You can watch it visibly bend during this point of travel.

I contend that if you were to disconnect the load cell entirely and place something on the pedal to measure the distance traveled and interpret it properly, you would not be able to tell the difference.

 

[mrbasher]

I agree that even with a load cell it is about pedal travel (as minute as it would be) and I agree it is about distance traveled. But in essence a load cell is more about pressure applied than distance traveled, for most of us humans we can regulate pressure much better than measuring how far we moved a pedal.

Though I guess if you wanted to you could also argue it is about pressure applied as well. Pressure x Spring tension giving you distance traveled. So pick any variable you would like.

It still seems as though you missed this statement I made above:

Let's say an example pot based pedal requires 20 pounds of force to achieve 100% braking. So 10 pounds of force would be 50% braking. How well do you think you can modulate that 10 pound difference between 0 and 50% or 50% and 100%? The answer is, not very well because you just can't easily feel this with your feet.

Now, increase this to 100 pounds of force for 100% braking. This seems to be a very reasonable level believe it or not. This means it takes 50 pounds of force to achieve 50% braking. Trust me on this, you can immediately tell exactly where the pedal is with your foot based purely on how hard you are pressing the pedal.

 

[Ripster]

It still seems as though you missed this statement I made above:

Let's say an example pot based pedal requires 20 pounds of force to achieve 100% braking. So 10 pounds of force would be 50% braking. How well do you think you can modulate that 10 pound difference between 0 and 50% or 50% and 100%? The answer is, not very well because you just can't easily feel this with your feet.

Now, increase this to 100 pounds of force for 100% braking. This seems to be a very reasonable level believe it or not. This means it takes 50 pounds of force to achieve 50% braking. Trust me on this, you can immediately tell exactly where the pedal is with your foot based purely on how hard you are pressing the pedal.

I agree with everything you are saying. I guess my thought is that any pots device has a rather large distance of travel associated with it, so no matter how heavy a spring you want to put on it you are still trying to manipulate that distance. Where with a load cell that distance is more finite and gives you the illusion of pressure rather than distance control.

I guess if you wanted to put an extremely heavy spring on your pots device and limit the throw (travel) to a very short distance it might not be too bad.

But with the load cell you know instantly when you start to apply the brake. That is the feel I don't get from a non-load cell brake.

 

[mrbasher]

I agree with everything you are saying. I guess my thought is that any pots device has a rather large distance of travel associated with it, so no matter how heavy a spring you want to put on it you are still trying to manipulate that distance. Where with a load cell that distance is more finite and gives you the illusion of pressure rather than distance control.

I guess if you wanted to put an extremely heavy spring on your pots device and limit the throw (travel) to a very short distance it might not be too bad.

That's basically all that is happening and it doesn't have to be a spring. There are many different types of materials out there and it's not necessary to use the full range of the pot. In fact, you don't have to use a pot at all.

 

[ravey1981]

What you are forgetting is that a real cars brake pedal is also position sensitive....

When you press the pedal in a real car first the pad moves to the brake disc. In this stage there is only a little resistance at the pedal and the pedal moves quite a lot. Then the pads touch the brake disc, the next stage is that you actually compress the brake pad material. There is now more resistance at the pedal and it moves only a small amount. Different pad material creates a different feel at the pedal as some compounds compress into the brake disc more than others. Any other movement at the pedal is due to expansion in the brake system (the brake lines etc)

So whilst what you feel is pressure all you are actually doing is MOVING the pad in relation to the disc...ie its position.

The only thing that stops the movement of the pedal is you're leg is not sufficiently powerful enough to move the brake pad (compress it) any further. If you used a hydraulic ram to move the pedal you would reach a point where something in the system would break, the pedal arm would snap, the lines would burst etc so its these factors which limit the movement of the brake pedal...

MOVE pedal more = more braking force = position sensitive

 

[Mahnegold]

Kudos to pilmat and mrbasher for pointing this out.

I had the same kind of ideas some time ago but I have not the ability to express all that stuff like both of you did. I am not a technician and also not English native speaker. So thank you guys for bringing this topic up. 👍

 

[kikie]

What it comes down to is that whatever you use, a pot, a load cell or a pressure transducer, the signal read ingame is still the same. It is just the "feeling" of the pedal that differs and you can modulate the brake much easier because it "feels" like the brake of a real car.

When insidesimracing reviewed the Perfect Pedal, shaun said:
"closer to how a real life brake works but still not the same".

I once read that the signal of a load cell/pressure sensor was converted to an electrical signal which is read ingame as it was a potmeter. I thought that the braking ingame is still the same what ever you use (pot or load cell/pressure sensor). Only the feeling of the pedal is different. I always wondered if it is that much of a difference ingame and if it is possible to not lock up the brakes, again ingame. As mentioned before, I also thought that the sim developers should emulate (program) the brake ingame the same as a real brake works i.e. pressure instead op distance (position).

I forgot about this until I just read this thread.

All the money spend on expensive hydaulic/load cell brakes is essentially a waste of money? You can easily use a piece of foam to emulate a real hydraulic brake?


ECCI once told me in an email exactly what is said in this thread. They use a brake pedal where is it easier to modulate the brake.


And there is still ABS in most sims. So won't won't lock up your brakes anyway. Except in Netkar Pro. No ABS there.


Question

If one uses a hydraulic brake, with a potmeter instead of a load cell, you probably can calibrate the brake in the T500RS's firmware? Because you will have less travel.
This is possible with the G27, even in windows, I think.

 

[ravey1981]

No need to use a pot instead of a load cell though as they both give out the same signal...as long as whatever you are using can be read/accepted by the board you are using (be it g27, ts500 or something such as Derek Speares board) then you are good to go.

Mr Basher has shown with his ts500 skateboard bushing mod that you can get a pretty realistic feeling brake using pots (well hall effect sensor, but the same thing really) and a suitably solid "spring"

The limiting factor with sim brakes I believe is the software itself. The problem we have is our brains can't interpret interia visually very well (which is the only way the sim can show it to us, along with sound of course)...this is a problem as we then can't judge how hard to brake. The sims therefore are not coded to interpret our actions at the pedal exactly as they are in the real world.

Try this....get in you're car, if you have one, roll along at around 10mph and then apply the brake to what you perceive to be "half way on" the car will jolt to an immediate halt. Now try that in a sim, the car will slow down but at a rate predetermined by the sim based on a pedal pressed to half travel (or half "pressure" if you're using a load cell)

If the sim tried to replicate the real world exactly we wouldn't know how hard to brake as because we cant feel inertia we can't feel how quickly we are slowing down at any given point....

Basically it boils down to this....say you're heading into a tight hairpin, you know you want 100% braking followed by easing off the brake in a controlled manner as you reach the apex of the corner.... what system is going to let your brain know what you're foot is doing most effectively? I say it is a stiff brake pedal by whatever means, whilst still retaining enough steps of resolution.... The advantage load cells and pressure transducers have over pots is that they allow more steps for a given movement at the pedal, thus enabling better modulation of the braking effort.

 

[kikie]

Well, after reading this thread I wanted to experiment (big word for trying something out ) on the SRW S1 wheel.

In Netkar Pro, I always lock up the front wheel while braking because there are no ABS settings (I thougt there were but I can't find the ABS anymore).
I have put a piece of foam behind the brake (operated by one's left hand) and hooray, Eureka etc... I use the brakes without locking up all the time.
It's not perfect but it's much better.

 

[oqvist]

ECCI decided against loadcells because they just don´t hold up as well and aren´t reliable enough. That was their explanation anyway. You need to replace them quicker then good potentiometers. And as they say you can simulate pressure sensitive brakes very well since real brake pedals do have travel. It´s not like braking on a plank. I suppose load cells higher precision comes more into play for those of us like me that like short stiff brakes. Not that realistic really based on the cars I driven but that don´t include much race cars just sport and regular cars.

About the load cell rave I suppose it´s because the first enthusiast mainstream or what to call it loadcell setup was rather good. I had the CSP V1 for a while. the brake in stock configuration had silly amounts of travel and was really nothing special over the G27. But setting it up for shorter stroke it was certainly very easy going even though I was at 100 % on the load cell setting. You couldn´t set it up for a really stiff brake but it happened to be just about my sweet spot. I compared it to my nixim modded G25 pedals at the time and the CST pedals. I clearly felt it was a considerable improvement over the nixim modded G25 pedals. Mainly due to the spungy effect on the rubber I like it to feel like I hit a plank so I know when I am at 100 %.

As for CST pedals they destroyed the clubsports in term of feel but I wasn´t faster with them. Partly due to the need for racing shoes I imagine but may also be the more realistic pedal travel. They are smoother and all that but a case of me not being able to take advantage I suppose

At that note I use the T500RS pedals now. Would love to be able to compare to my old clubsports but I can quite well mimic the brake on a plank feel by going by the short travel mode on the T500RS with the realistic brake mod. At full travel mode it feel much more natural then my clubsports despite the noise and feel from the spring and I believe also in short travel mode. Hoping to try mrBashers mod in the near future so I can do without it

I only use about 25 % of the potentiometer in the short travel mode but on quick testing don´t seem to do much harm precision wise. You get quicker to 100 % braking and sometimes it feel easier to modulate by easing off in smaller then larger scale. My experience is that it certainly is easier to modulate by muscle memory then position memory.

I am a bit hesitant to get the loadcell mod for the T500RS though. It´s on the expensive side of things and will have to budget for replacing it and I am not sure I will see any improvement. Particularly if I can get an equal feel without having to feel that spring in operation with some bushings instead.

It would be interesting with a brake that has no travel at all and where you only go by pressure.

 

[RacerXX]

You don't feel inertia when you brake in real life. You feel g-forces, vehicle yaw, and front tire traction limits via the changes in steering forces felt by your hands. And you see the change in corner entry line as you brake and steer. While possibly hearing tell tale sounds from the tires.

So, virtually and without a motion rig for g-force and nothing for yaw we have leg pressure/position, change in line, tire sound, and change in steering forces to reconcile. IRL brake feel changes when you have lock up too.

You can use better load cells than those salvaged from bathroom scales. Part of why they break is that they are being overloaded which involves bending the steel too far. Better sensors and revised articulation to stay within a sensor's safe limits would solve that.

You can use a BMW hydraulic sensor for around 75 bucks to directly measure pressure (0-5 volts) if you add a hydraulic cylinder to a braking rig. That could allow near zero foot travel once slack is taken up. You'd want some transfer function work with that signal and a means to inform the driver what's going on via brake feel, steering feel, sight and sound. Ideally with both motion and yaw.

 

[fatkrakr]

While Im not disagreeing with whats being said here I do think your missing why most are upgrading. Its not to change how the game reads are imputs, but how the pedal feels under foot. I could care less how the signal gets sent to the game, just that the pedal feels as realistic as possible. Nothing is going to be perfect, but pressure based systems FEEL better than position based systems. No need to reinvent the wheel, just make it a little rounder.

 

[Cote Dazur]

You don't feel inertia when you brake in real life. You feel g-forces, .

Not true, Whenever you accelerate, you feel a gravity-like sensation "pulling" you in the direction opposite your acceleration. What you feel isn't really a force--it's really just your own inertia trying to keep you going in a straight line at a constant speed. In other words, your inertia is trying to keep you from accelerating. For example, whenever you turn left in a roller coaster, your inertia opposes your leftward acceleration and you feel "pulled" toward the right. This "pull" of inertia is sometimes called a "fictitious force" but you should remember that it isn't a force at all, no matter how "real" it feels. Perhaps the most striking effect of acceleration occurs during your trip around a vertical loop-the-loop. When you are arcing around the top of the loop-the-loop, you are accelerating downward so quickly that you feel an enormous "fictitious force" upward. This "fictitious force" has a stronger effect on you than the real force of gravity, so you feel as though you are being pulled upward. The result is that you feel pressed into your seat, even though your seat is actually upside-down.

But with the load cell you know instantly when you start to apply the brake. That is the feel I don't get from a non-load cell brake.

I agree with you ripster, althou this thread is very interesting and very well documented, I think it will mislead some readers in thinking using potentiometer braking anf load cell braking is about the same, it is not. Potentiometer is about travel, trying to mimick pressure with a potentiometer playing with stronger spring or rubber busher might add to the immersion since pressure is involved in real life breaking, but I doubt it adds anything to the precision that is needed to know where the potontiometer is at so you know how the brake is going to react.
With load cell it all about pressure, with a little travel to add to the reality, but ultimetly it is the pressure ( force applied) not the position that dictate the amount of breaking. This reasult in a very different experience, not like but closer to what happen when braking IRL.
So load cell is not marketing, it is a good system to emulate braking in a SIM.
You can be as fast with one system or the other, you might even be as fast with a controller, this is beside the point, they all send a voltage to the SIM, that is also beside the point.
I would be curious to hear from user of load cell brake that went back to potentiometer and why.
Now if some one come with a new solution, other than potentiometer or load cell, that mimick the real bracking experience, I have no doubt a lot of us will be very attentive. As today's solution are still very far from the real thing.

 

[pilmat]

While Im not disagreeing with whats being said here I do think your missing why most are upgrading. Its not to change how the game reads are imputs, but how the pedal feels under foot. I could care less how the signal gets sent to the game, just that the pedal feels as realistic as possible. Nothing is going to be perfect, but pressure based systems FEEL better than position based systems. No need to reinvent the wheel, just make it a little rounder.

A load cell is not pressure based, it measures strain in the form of a deflection in a pieces of material (usually metal). Basically it is only a really stiff spring with a way of measuring how far you've deflected it, just like a pot measuring how much you've compressed the spring.

So a spring with a pot IS a load cell It's just a "softer" one!

The thing I like with the GTEye spring is that it is tuned to get to it's third and stiffest stage about where iRacing "locks up" on most cars. So it is easy to modulate from there, especially with a Bodnar cable.

 

[fatkrakr]

A load cell is not pressure based, it measures strain in the form of a deflection in a pieces of material (usually metal). Basically it is only a really stiff spring with a way of measuring how far you've deflected it, just like a pot measuring how much you've compressed the spring.

So a spring with a pot IS a load cell It's just a "softer" one!

Perhaps, but your still using pressure with a load cell to determine brake force instead of position to determine it.

 

[Cote Dazur]

A load cell is not pressure based, .

This is very misleading: A load cell is a transducer that is used to convert a force into electrical signal, does not really matter if it is a Hydraulic Load cell , Pneumatic Load cell or a Strain Gauge Load cell.

http://en.wikipedia.org/wiki/Load_cell

just like a pot measuring how much you've compressed the spring.

The potentiometer does not measure the spring, the spring pushes back the pedal in the original position, the position of the pedal/potentiometer determines what current is sent.

 

[kikie]

While Im not disagreeing with whats being said here I do think your missing why most are upgrading. Its not to change how the game reads are imputs, but how the pedal feels under foot. I could care less how the signal gets sent to the game, just that the pedal feels as realistic as possible. Nothing is going to be perfect, but pressure based systems FEEL better than position based systems. No need to reinvent the wheel, just make it a little rounder.

Quite right but you can get that 'realistic feel' with having to upgrade to an expensive hydraulic system. But a hydraulic system or a load cell brake has it advantages over a potmeter.

 

[pilmat]

This is very misleading: A load cell is a transducer that is used to convert a force into electrical signal, does not really matter if it is a Hydraulic Load cell , Pneumatic Load cell or a Strain Gauge Load cell.

http://en.wikipedia.org/wiki/Load_cell

It's not misleading at all! You confirmed it measures load (force) and not pressure

The potentiometer does not measure the spring, the spring pushes back the pedal in the original position, the position of the pedal/potentiometer determines what current is sent.

You're right, it doesn't measure the spring directly. But it does measure how much load you've put into the spring (spring rate * distance compressed = force). Just like a load cell, you are outputting a voltage for a distance displaced.

 

[Cote Dazur]

It's not misleading at all! You confirmed it measures load (force) and not pressure

OK, what force is it measuring then, if not pressure?

You're right, it doesn't measure the spring directly. But it does measure how much load you've put into the spring (spring rate * distance compressed = force). Just like a load cell, you are outputting a voltage for a distance displaced.

So if you are right, if you remove the spring it does not work anymore, as there is no load to measure any more. Just like a load cell.

If I am right, remove the spring, move the pedal by hand, and you will see that the SIM does not know that the spring is gone and just react to where the potentionmeter is at in its travel. Not at all like a load cell!

Edit: thought I would add alittle more info for those interested.
A load cell is a transducer that converts mechanical force into electrical signals. There are many different types of load cells that operate in different ways, but the most commonly used load cell today is the strain gage (or strain gauge) load cell. As their name implies, strain gage load cells use an array of strain gages to measure the deformation of a structural member and convert it into an electrical signal.

Pressure transducers operate under the same principle. Strain gages, mounted on a diaphragm where the pressure is applied, measure the deformation of the diaphragm that is proportional to the pressure. The following sections describe the principle of operation of strain gage load cells and how to make a measurement from them, although the same applies for strain gage pressure transducers
http://www.ni.com/white-paper/7138/en

 

[pilmat]

OK, what force is it measuring then, if not pressure?

Pressure = force / area. What area ia the load cell measuring? It only measures force.

So if you are right, if you remove the spring it does not work anymore, as there is no load to measure any more. Just like a load cell.

If I am right, remove the spring, move the pedal by hand, and you will see that the SIM does not know that the spring is gone and just react to where the potentionmeter is at in its travel. Not at all like a load cell!

But you can't drive without the spring

 

[Cote Dazur]

Pressure = force / area. What area ia the load cell measuring? It only measures force.

So if I understand you correctly, it is measuring how much force I applie with my foot. I think we agree then. My mistake, I thought I was applying pressure with my foot when I was only applying force. I stand corrected.

But you can't drive without the spring

I know people driving the potentiometer brake with squach ball and bundgge cords instead of springs, but that would make me facetious, you are correct very difficult to drive without the spring without taping the pedal to your foot.

 

[pilmat]

taping the pedal to your foot.

I can just imagine what this would look like!

 

[Zathra5_]

This is an interesting discussion and something that I've been thinking about. I have a bunch of ideas but will just write about a few right now. First, if your pedal system has a spring with a fixed stiffness, a pot and load cell should give you similar results. If you press with x amount of force you get y amount of pedal deflection, if you press with 2x amount of force you get 2y amount of pedal deflection. That will change if spring stiffness changes with compression. If the spring gets stiffer, the more you push, at full braking you will require more force for a given amount of deflection. A pot in this instance will be less sensitive than a load cell since the load cell is still measuring force while the pot is measuring deflection. Things change completely if you add viscoelasticity to the system. The force and distance will no longer be directly related.

 

[mrbasher]

There still seems to be some confusion in this thread and I can't really understand why. (not Zathra5_ , that is correct)

If we boil a pot based pedal and a "pressure" based pedal down to their essences, we get two pedals that require a specific amount of pressure to achieve a specific amount of braking. Even if you remove the spring from a pot based pedal, it STILL takes some kind of force to move it, however slight. Now don't quit reading here and post a response please!

Stop for a moment and imagine if both pedals required the same exact amount of force to achieve 100 percent braking and that the travel on those two pedals to achieve that braking level were identical. (and yes, they can be) What would be the difference?

People seem to get stuck on what or how the sensors measure what is going on. The result is identical if the forces are identical. The forces are what really matters.

You have to get traditional pot pedal braking out of your head. Yes, this is in fact based more on position than pressure. However, this is only because there is not enough resistance on the pedal.

Lastly, it's not generally enough to simply stuff a stiffer spring or a rubber ball in a pot brake. It works better, but you lose full travel. However, there is a simple solution to this problem and it's works just fine. I spoke of this on the ISR forums some 6 or more months ago and I apologize but I won't detail the circuit necessary here.

I think the only real solution here is to just finish developing a brake pedal that doesn't use a pressure sensor and let people use it. Until then, people will trust what manufacturers of pressure sensitive pedals are telling them outright.

I'm here to tell you, it's about how the pressure is delivered and how much, more than anything else.