Pressure sensitive brake pedal for the LWFF

Quite a while ago a guy on r.a.s. asked for a brake pedal, where the brake effect isn't controlled by the pedal travel, but by the pedal pressure against it's dead end. This of course is the classic type, where no brake servo is involved. During its travel the pedal builds up slight pressure to the brake system. When the hydro-lock is reached, full pressure can be applied to the system without any significant additional pedal travel - it blocks.
Unlike this r.a.s. guy I appreciate a certain pedal travel in the hydro-lock range, since there are always some flexible components involved, e.g. brake pedal, brake lines, levers, brake pads or shoes or some residual air inside the system. Those "faults" act like a very stiff spring.
To check this out at home, pump the brake pedal of your car until full pressure is build up (engine off to disable the brake servo). Release the pedal and press it again, slooooowly. First you find a certain travel without any significant resistant. In this range brake pressure is build up too, but only very low. When you reach the dead end (pedal blocks), you still find some flexibility in the pedal, due to the a.m. flexible components.

NOW, what does this mean for my GPL at home?
To simulate the true thing, I only have to arrange the dead end of my brake travel a little flexible and put the tire-lock into this range.

First part is not so easy, since the squashball trick (I know, only the yellow Dunlop works ;-) doesn't fit to the Logi. But when opening the pedal unit, you find it very inviting to put something into the brake spring, which does the trick. Originally I wanted to use a very stiff and short spring, but due to -no have lah- I searched for some rubberpieces to place there.
To cut a long story short: PVC is to hard, insulation foam (sp?) to soft, silicone or soft rubber is quite right. You should be able to get a doorstopper or whatsoever, which can do the job.
First I modified this bit-magazine you can see here. This gives you a flexible "end" of about 1mm. Later I exchanged to a much wider "end", since 1mm was not enough to get a steady setting - too sensitive in adjustment.
Anything below 1 mm isn't recognized by the Logi driver as valid travel at all.

Second part now is a little tricky. The wonderful (flexible) hydrolock doesn't help at all, if the tires don't lock in this range. According to Murphys law, there is no chance to get it work properly right now.
So we have to cheat the wheels electronics about the position of the pedals dead end or about the actual pedal position.
Should be no problem, since the pedal position is measured by a pot. Only mix some additional resistance to the pot either serial or parallel, make the thing adjustable and capable of being switched off (for pedal-calibration).
(Readers suggestion, thrown in during July 00: No need to solder anything, since the limits can be adjusted with DxTweak, available from the Wingman Team at http://www.wingmanteam.com
Haven't tried it myself, but sounds good.)
Again the short version, until the pictures are available:

A 20K cermet trimmer (this thing with the spindle inside), soldered inline into the brown wire (brake-pedal side) did the trick. You also have to solder in a micro-switch to bridge the trimmer contacts for the calibration procedure.

Now GPL fired up and pedal calibration with bridged trimmer. In the car, switch back and adjust the trimmer to your liking, while steering with your teeth ;-)

And now my confession:

I raced all the time with brake help ON!!!

I only have one excuse, which is the "outstanding" Logi pedal unit.
(But nevertheless the laptimes were quite ok, weren't they?)

NOW ITS OVER!!!           hopefully

If anybody doesn't understand my cryptic descriptions, either email me or wait for the pics, cirquit diagrams,...

Dec 99: 
Doorstop update

I put in a "13mm" doorstopper today, this thingies made from red rubber. This thing is quite high, about 22 mm. The compressible height is about 12 mm. This decreases my pedal throw quite much (who needs pedal throw, if he has a pressure sensitive pedal?), but is needed to give enough travel in the compression range. If I can find some softer rubber, would be better.
I also exchanged the trimmer for a 10K one, since it gives me a more sensitive adjustment and less fluxion due to environmental influences (e.g. hot or moist feet). In my case 10K is enough, but depends on the setup. Better to start with the 20K, but buy a quality trimmer.

Next step was to install switch and trimmer in the unit, since I hate this cables hanging around. I planned to put both into the wheel unit, due to better accessibility (took me 5 min to spell this word correctly), but I don't have any idea which line (wheel to pedal unit) I could abuse for this. Let's see, probably  later.
So I glued the trimmer into the pedal unit, accessible by screwdriver through a small hole and also fixed the switch there.

Test driving was a blast, now you find your brake-point (the pedals one) immediately. I adjusted the trimmer, so that the tire squealing just starts, when pushing the pedal down to the stopper. Any further pressure, which you don't recognized as pedal-movement, brings you over the adhesion-limit.  

Jan 00: 
Calibration Update
I found an easy way to calibrate reproducible.
1. Switch the trimmer to bridged
2. In calibration mode press the break pedal by hand (more sensitive) down to doorstop-touch (not further)
3. Release and calibrate the rest
4. Exit calibration menu
5. Switch back to trimmer-mode

Works fine.

May 00: 
Big feet on small pedals by Paul Fimple Jr.

June 00: 
Loosing ca. 20% of the throttle

Ernie brought it up again:

<snipped away his appreciation of the BB-kit ;-)>
> It seems to get worse with use in an evening and I also lose 10% of the
> throttle travel after
> it has been on for a while (like the middle of an online race !!!) and
> if I reboot, the problem
> goes away for awhile again.
>
> Last night it did it at the end of qual and rather than exit the race
> and reboot, I disconnected
> the cable to the wheel, went into GPL options and reset and calibrated
> the controls, and it
> worked fine for about 3/4 of a intermediate race at Zandy.
>
> My first thought on the lose of throttle travel was a thermal prob with
> the pot, or the spring or
> something was binding, but since I found the problem goes away for
> awhile if I reboot I don't
> think either of these are the cause.
>

<snip>

Ernie, I know this effect very well :-((
I have my second Logi right now and both showed this regular loss of ca. 20% throttle after about half a year usage.

I found out the following (kind of not refuted theory):
The throttle spikes from time to time (over maximum limit) and sets the upper calibration limit new. Depending on the strength of the spiking you have more or less throttle left at full throttle deflection.

I solved (don't laugh) the problem as follows:
Due to lack of new pots I just replaced brake and throttle pot. No more probs since then on both wheels.

Just try it out. It's a bit mystic, but as long as it works?

Aug. 00:
Pedal-conversion by Gary Johnson 

following we had some interesting email discussion:

and here we go again:

<snip>
Perhaps, I was not a very good communicator here. Here's my routine:

1. Trimmer is Always in the circuit
2. Turn trimer to max resistance ( in this particular case, open
circuit.
3. Go to calibration screen in GPL
4. Fully depress brake pedal (I calib. gas and steering also) and hold
it down.

At this point I get no meter reading on the brake calibration meter.
Because effectively, I have an open circuit. No voltage is getting back
to the computer. So the computer thinks that the brake pedal is not
depressed at all. This may only work when the trimmer you are using is
in the 200K  + ohms range.

5. Start turning trimmer resistance down as I watch the calibration
meter(the brake is still fully depressed). As the resistance is lowered
on the trimmer (voltage to the computer is increasing) the meter starts
to register. I continue to lower the trimmer resistance until the meter
reaches a full scale reading. and clik OK on the calibration screen. If
I continue to lower the resistance in the trimmer, I don't gain anything
because the meter will not read any higher. At this time the resistance
on my trimmer is approx. 1.2K ohms.

<snip>

My adjustment in the car ends up with a trimmer resistance in the 250
Ohm range. But this is my method. Since the calibration is fixed,
movement of the trimmer only affects what GPL thinks the brake pedal is
doing. So I pick a long staight (Monza) and turn the trimmer to high
resistance (no voltage, no meter reading when I was in the Calib. mode)
and run down the straight. Put on the brakes, and get ....what....no
brakes because the computer isn't getting any voltage. Ok. high speed
run, hit the brakes to my secondary spring resistance point, turn
trimmer down in resistance until tires squeal. I'm done. Now I can lock
the brakes by pushing past the 2nd pedal spring point, and by turning
down the resistance on the trimmer a little more, I can increase the
braking force at the second spring point if I wish to.

 
> Your approach for reducing the free travel probably deserves another
> trimmer, serial in the other outer pot-pin. Since both outer pins are in
> use, I guess the electronic always uses the low-resistance measurement for
> zero AND full deflection, since the high resistance (lets say 100k +- 10%)
> is not stable enough.

Don't think so Jens. The other outer pot pin is being used (I believe)
when the pedals operate in the single axis mode, with one pot (gas)
increasing voltage, while the other pot (brake) decreased voltage to the
same input pin of the computer. As the pot moves, one outer pin starts
with high resistance and moves to low, the other outer pin starts with
low resistance and moves to high.

Agree completely with you that my trimmer is way too big in it's range.
It IS difficult to adjust with any precision in the resistance range I'm
using, but I couldn't find a 20K trimmer in this small town and used
what I had (it was a dimmer pot from a halogen floor lamp) to see how
I'd like it. I will be replacing it, and in fact I think even a 2K would
work by my readings. I'll let you know what I get and how it works.
Thinking about a smaller trimmer. when in the calib screen, with the
pedal depressed I can (by adjusting my trimmer) make the meter read zero
to full scale. With a smaller trimmer, I would see how much the trimmer
could make the meter move. If it could not reduce the meter reading, I
would just calibrate at full brake depression and full trimmer
resistance. Then if I couldn't get the response I wanted in the game, I
would assume the trimmer was too small.
By the way, tried to get the brakes to lock again using the trimmer
alone, and I couldn't do it. Maybe I was dreaming.
Still experimenting with springs.

Gary

Oct 00:
Update Pedal conversion by Gary Johnson

----- Original Message -----

<snip>
> On another front, Jens, I think I should update you on my brake
> modification and use. As I think I had said before I used a 5K ohm pot
> wired as you had done, with a bypass switch, but in use, the bypass
> switch has become redundant as I never use it, so the new unit will only
> get the 5K ohm pot. To calibrate the pedal, I press the brake pedal to
> its full travel and adjust the pot so that I get a full scale reading,
> then click OK. In the game to adjust the lockup point I need only adjust
> the tuning pot. Along with fitting a shorter smaller spring inside the
> original brake spring, this gives me a pedal that has a light initial
> travel, then a stiffer pedal with the lockup point being just past the
> point the pedal action stiffens up. Depending on car and setup, I may
> need to fine tune the brakes to get the maximum feel/efficiency
> combination, but this is really fine tuning.
<snip>

Sept.00:
Adjusting the pressure sensitive brake with DXTweaks

finally I tried this: 
Instead of fooling the electronics by mixing some resistance to my brake pot I used the a.m. tool from Wingman Team to do the job. What started promising (you are able to decrease the brake maximum by decreasing R(min) below zero), didn't work at the end.

Problem: 
In my pedals (doorstop inside®) the last few percent of full brake deflection don't produce readable signal for the electronics - in Windows calibration the pointer doesn't move in this range. In a system w/o doorstop this should be even worse, check it out for yourself. 

What does this mean for daily life:
I can adjust the brake maximum to a certain value, but I'm not able to overlap this maximum (tire-squealing to tire-locking) with my beloved rubber-range (where the doorstop increases the spring-tension)

Solution:
Have to buy a higher doorstop. Will cost me another estimated 15 cent.... but what's another mortgage on my house compared to the real feeling on the pedals ;-)