Are pneumatic pedals as reliable as those based on elastomers? (NT)

[Elaphe]

I had a set of sprints I bought for a rig for one of my sons, I didnt spend a lot of time on it but the he brake and throttle are quite a bit better on the ultimates to me. The throttle was nicer and the brake more configurable. The bad news, the brake still has a small not very comfortable pedal face. If you are not planning to use more pressure than your sprints I dont imagine it to be an issue in socks, if you wear something like aqua shoes its even better.
I use an aftermarket pedal face and it is a huge improvement for me as a sock racer but that is also because I use higher braking forces. I don't see how you could be unhappy if you can swallow the price. They are also quite easy to attach things to, I have two exciters on the throttle and two exciters and an earthquake mqb on the brake... All easy to come up with a simple mounting solution for these pedals.

I use Sparco shoes. What aftermarket pedal faces are you referring to? I know the HRS but they are no longer on sale.

 

[metalnwood]

I have these, they do have a two pedal set as well... Its all extra $ but they are nice.

HRS V3-3P pedal pads for Heusinkveld Ultimates and Pros

NOTE: Australian customers - 10% GST will be added at checkout NOTE: International customers - import duties into your country will be at your expense, and will be your responsibility. The HRS billet aluminium 3D-V3 machined Pedal plates are a direct replacement for the Heusinkveld Ultimates &...

hrsims.com

this would be the set it you only use 2 pedals

BIG FOOT SERIES Ultimate + 2 Pedal set, incl foot support. Now available with optional extra Clutch!

NOTE: Australian customers - 10% GST will be added at checkout NOTE: International customers - import duties into your country will be at your expense, and will be your responsibility. The HRS 2P V3 billet aluminium 3D machined Pedal plates are a direct replacement for the Heusinkveld Ultimates...

hrsims.com

 

[Deleted member 197115]

Accidentally I happen to have HRS 3 pedal set for HE Ultimate/Pro with gas pedal guard lying around. Great set only useless on Simtrecs.

 

[Spinelli]

There was a PDF document made by high-end Italian simracing pedals manufacturer, ARC, that explains why they believe, for simracing purposes, that pneumatic is actually superior to hydraulic. This was around 7-12 years ago. I wish I could find the document for you.

By the way, rubbers/bushings/elastomers suck.

For the last 15 years, I've tried a million loadcell brakes with elastomers and couldn't figure out why I couldn't get the same sort of dead-on precision, control, and especially consistency that I get with all my non-loadcell pedals (especially when the non-loadcell pedals are modded to have stiffer resistance). I started to believe that the problem was that loadcell pedals were bad for simracing because the pressure-based philosophy just doesn't work good when you cannot feel the constant minute changes in longitudinal g-forces like in real life. I later discovered that that theory of mine was incorrect. Every non-loadcell pedal I ever tried used springs and every loadcell pedal I ever tried used elastomers. When I finally tried loadcell pedals with springs, my braking was fantastic again just as it always was with non-loadcell pedals. Therefore the problem wasn't using loadcells, the problem was using elastomers.

There's a video by Race Beyond Matter or something that explains the very issue with elastomers:

I discovered this many years ago and tried posting about it in many forums. Just like with many physics discussions/issues I've brought up, you just get attacked by most people. Now, years later - just as has happened with many physics faults/issues I've brought up - others are finally realizing/admitting/fixing the issue which I tried to tell people about ages ago.

 

[Neilski]

There was a PDF document made by high-end Italian simracing pedals manufacturer, ARC, that explains why they believe, for simracing purposes, that pneumatic is actually superior to hydraulic.

I have very limited personal experience with pedals (couple of flavours of Logitech is all).

However, I'm struggling to understand how a pneumatic system would differ significantly in use/feel from a simple mechanical spring + position sensor.

 

[Spinelli]

I have very limited personal experience with pedals (couple of flavours of Logitech is all).

However, I'm struggling to understand how a pneumatic system would differ significantly in use/feel from a simple mechanical spring + position sensor.

This link is dead but maybe there's a way to use it to find the document somewhere online:

http://www.arc-team.it/shop/images/files/Carbon_Pedals_-_The_reasons_for_the_choice.pdf

Maybe Sim Racing Garage gives some insight:

 

[Neilski]

This link is dead but maybe there's a way to use it to find the document somewhere online:

Didn't find anything much useful sadly, but it was worth a shot. (I found a few old forum posts around the web, linking to it.)

Maybe Sim Racing Garage gives some insight:

Yes, some good info there.

Nicely engineered pedals but ultimately I'm actually more confused now than before
This is because when @Elaphe initially asked about pneumatic pedals, I assumed that the pneumatics would be taking the role of the spring. However, the ARC Carbon pedals appear to use the air both as a damper and a spring, depending on how the valves are set up, and of course they also have plain old metal springs which I suspect provide the main resistance (very large one on the brake, for example). So I'm unsure whether these actually qualify as pneumatic pedals...

Meanwhile, it has occurred to me that there are reasons NOT to want to use the air as a spring: because it's compressible, the air will heat up as you push the pedal down and do work on it. That increased temperature will transiently increase the spring force. As the heat bleeds away into the cylinder housing (without you even moving your foot), that force will reduce again. So this doesn't seem like a great recipe for consistency. [Caveat: I'm not sure how long the time constant for the cooling down will be, and that will probably make a big difference to the importance or not of this effect.]

So... I'm seeing obvious reasons to prefer plain springs over air springs - simpler (no seals), more linear (and no pedal-speed dependence for the spring force). Other than damping though, I'm seeing no benefits to adding pneumatics. I guess I am probably missing the point?
(Tbh, I can't even see any real benefit to going hydraulic either - the linearity will be better than pneumatics in that the fluid won't heat up, but where's the benefit over springs to justify the hassle with sealing, the need for bleeding, the risk of getting fluid over your floor? Again, I guess there must be some benefits I'm missing, above and beyond a wee bit of damping which you could mimic with an add-on strut )

 

[Deleted member 197115]

My experience going from "fresh" elastomers to springs on the same load cell pedal set (Simtrecs) was just better controlled trail braking, my guess that's because springs have faster rebound than rubber.
Consistency and everything else was in the same ball park, and springs should have better longevity without typical over time elastomers degradation.

 

[stigs2cousin]

I don´t think the air volumes involved will heat up much as frequency and piston speed are quite low, quite different from the pump we use to inflate our bicicle tyres.

I see the problem more with reliability and stiction of the piston seals as airpistons with low to zero circulation are difficulte too keep lubricated.
Both goals are more easily achieved with hydraulics because the hydraulic fluid doubles as lubricant.

Hydraulic pedals do feel real because the movement of pistons and fluid is real.

But I think that one can only feel that when "dryhumping" the pedals, when racing all we need is a reproduceable reaction to our inputs and all the rest is placebo.

(that said, if someone would sponsor me a set of Aschley´s I´d conduct a very thorough evaluation including a double blind study )

 

[Neilski]

I don´t think the air volumes involved will heat up much as frequency and piston speed are quite low, quite different from the pump we use to inflate our bicicle tyres.

I see the problem more with reliability and stiction of the piston seals as airpistons with low to zero circulation are difficulte too keep lubricated.
Both goals are more easily achieved with hydraulics because the hydraulic fluid doubles as lubricant.

Yeah I'd agree about the seals being a concern for pneumatics.

Are there actually any pedals out there that don't use any metal springs, but just pure pneumatics? I'm starting to suspect not, because to have any resistance at the very start of the pedal stroke, you'd need to have the pressure in the cylinder above atmospheric pressure, and that would naturally want to leak out, so you'd need to somehow top it up... (Automatic top-up might be doable I guess.)

As for the heating creating non-linearity, I don't think it's about frequency (pedal may be pressed quite infrequently for sure) as much as piston speed, and the time taken for the heat to be lost to the cylinder - that's the bit I haven't attempted to calculate.

For fun though, I just did a quick estimate (using this site) to see how big the effect is when you have pure adiabatic compression of air - i.e. no heat lost to the cylinder walls: if you depress the pedal far enough to shrink the volume of the cylinder by a factor of 2, the pressure in the cylinder (and thus the force on the pedal) would go up by a factor of more than 2.6 and the temperature would rise by almost 100 deg C (if it started at room temperature). As the air cooled down again, the pedal force - if you could keep your foot in the same place - would drop by a factor of 1.3. Ouch...
(Of course, the other extreme would be that the heat could leak out fast enough that the air doesn't warm up at all, and then the pressure in the cylinder would rise by exactly a factor of 2.)
The adiabatic case gets considerably more extreme as the volume ratio increases - a factor of 4 reduction in volume would boost the pressure by a factor of almost 7 (temperature rise is then around 237 deg C)

 

[blekenbleu]

I'm seeing obvious reasons to prefer plain springs

The only drawback I imagine is the hassle of getting 3 spring rates right:

• before any pads touch discs (and/or shoes for drums)
• while friction surfaces are engaging
• caliper and line flex while applying greater pressure until lockup
  

 

[Neilski]

The only drawback I imagine is the hassle of getting 3 spring rates right:

• before any pads touch discs (and/or shoes for drums)
• while friction surfaces are engaging
• caliper and line flex while applying greater pressure until lockup

Fair point, but personally I am not sure I would notice (while racing) those effects being present or missing.
Another way to look at it, thinking toward the future of racing: if I were driving a real race car with full-on brake-by-wire (let's say purely regenerative, for fun) and a load-cell brake pedal with which to modulate that system then would I miss the feel of the traditional hydraulic moving-pad braking system? I reckon nope.

 

[blekenbleu]

Another way to look at it, thinking toward the future of racing: if I were driving a real race car with full-on brake-by-wire (let's say purely regenerative, for fun) and a load-cell brake pedal with which to modulate that system then would I miss the feel of the traditional hydraulic moving-pad braking system? I reckon nope.

Real cars generate acceleration when the pedal is pressed,
which is why I value harness tensioning, but still want pedal feedback.
Just as with digressive clutch, it is not *consciously* sensed when shifting on track,
but I still suppose that it helps, since much of driving is not conscious...

Our Prius has about as numb a brake pedal as can be imagined.
On ice, sensing lockup by the pedal is impossible.
Without ABS and traction control, it would be uncontrollable.

 

[RasmusP]

Tbh, I can't even see any real benefit to going hydraulic either - the linearity will be better than pneumatics in that the fluid won't heat up, but where's the benefit over springs to justify the hassle with sealing, the need for bleeding, the risk of getting fluid over your floor? Again, I guess there must be some benefits I'm missing, above and beyond a wee bit of damping which you could mimic with an add-on strut )

After using some hydraulic, spring loaded, elastomers and spring + elastomer + hydraulic dampers pedals at the Simracing Expo, I can say:
I want a hydraulic damper for my brake pedal!
My biggest braking issue is that when I start to reduce the pressure on the brake, I instantly jump down was too much.
The brake pedal just springs back almost instantly.
With a little bit of a hydraulic damper support, the pedal comes back just a little tad slower, resulting in a much smoother trailbraking.
In reality, you have the G forces pushing your leg and body forward. When reducing leg pressure, you'll still "hang in there".
But in a Simrig, relaxing your leg a tiny bit can result in the tension basically collapsing for the first 60%.

This gets better, the higher the needed brake pressure is, but I must can't deal with it in socks and my foldable F-GT Lite.

Fair point, but personally I am not sure I would notice (while racing) those effects being present or missing.
Another way to look at it, thinking toward the future of racing: if I were driving a real race car with full-on brake-by-wire (let's say purely regenerative, for fun) and a load-cell brake pedal with which to modulate that system then would I miss the feel of the traditional hydraulic moving-pad braking system? I reckon nope.

In a real car, nothing really matters since you FEEL the result with every atom of yourself
For me, it helps a lot of the brake feels similar to a standard road car, since that's what my leg learns in everyday life.

 

[stigs2cousin]

In reality, you have the G forces pushing your leg and body forward. When reducing leg pressure, you'll still "hang in there".
I want a hydraulic damper for my brake pedal!
My biggest braking issue is that when I start to reduce the pressure on the brake, I instantly jump down was too much.
The brake pedal just springs back almost instantly.

I was wondering about that and planned to ask for Motec to prove it, but that cleared it up:

This gets better, the higher the needed brake pressure is, but I must can't deal with it in socks and my foldable F-GT Lite.

In reality, you have the G forces pushing your leg and body forward. When reducing leg pressure, you'll still "hang in there".

Nope, I won´t start that discussion again

 

[Enzo Fazzi]

Nope, I won´t start that discussion again

Rasmus didn't say it adds any significant braking force, just that your leg kinda stays there. Can't really argue with that.

 

[RasmusP]

Yep, please no discussion about making "braking hard enough" easier due to G-Forces!
I really just wanted to say that I can control the reduction of my leg tension better, when I'm "hanging in there" instead of the "instantaneous collapse" of the tension in my "low force rig".
But honestly it also might just be that I feel the G's and won't instantly drop them as easily since I would get thrown around in the seat although wanting to be smooth.

Anyway, it's way easier for me if I can move my foot a bit backwards before the tension collapses. Or if a damper helps me at the initial reduction of tension!

I was wondering about that and planned to ask for Motec to prove it, but that cleared it up:

I forgot to add: I tried them all yesterday at the Simracing Expo. I would've loved to get my telemetry dump from the different stands but sadly that wasn't possible.

 

[Deleted member 197115]

"Some say when he sees a pretty lady one of his legs is getting bigger." J.Crarkson the Stig's intro.

 

[stigs2cousin]

Rasmus didn't say it adds any significant braking force, just that your leg kinda stays there. Can't really argue with that.

We had a prolonged discussion about that on R.D. because my personal experiences didn´t corroborate the discussions on the internet.

But these experiences were limited to two cars ( personal GT86 on semi Slicks with stock seat and 4point harness and our Club e36 on racing slicks with containment seat and 6point harness.)

In both cases my upperbody felt the pressure from the belts, my "derriere" and legs in the seat in´t feel like they moved under the brake G´s.

No Motec available, my HLT ( Harrys Lap timer) traces didn´t have the car integration that is possible with AC Motec.

But that will not restart the discussion again, we curtously agreed to disagree

 

[stigs2cousin]

"Some say when he sees a pretty lady one of his legs is getting bigger." J.Crarkson the Stig's intro.

Thats a wonderfull quote to end the discussion!!