brake pedal load

[adfec]

Hi,
Does anyone have references on brake pedal load?
I'm designing our brake system and we always used 150 lbs as load. But I heard someone, don't remember who, talking about a load increase of ~= 100 lbs/ g...

Is anyone heard off it??

[adfec]

Hi,
Does anyone have references on brake pedal load?
I'm designing our brake system and we always used 150 lbs as load. But I heard someone, don't remember who, talking about a load increase of ~= 100 lbs/ g...

Is anyone heard off it??

[Conor]

150lbs is quite a bit....

[CappyUMD]

Brake pedal load can be whatever you want it to be. If you're not sure about the 100 lbs/g quote then go to a gym and use a leg press machine. Press 100 lbs with your left leg and ask yourself if that's a reasonable effort for 1 g.

If your brake system is already designed then calculated the required force at the pedal based on your braking system parameters.

[rjwoods77]

You also have to consider your pedal ergo. Most cars in the FSAE comp have a flat leg driver postion. This being the legs of the driver are almost laying flat on the floor of the car. At this point you arent braking with you whole leg. It is mainly your ankle and calf muscle. I would say no more than 100lbs at full lockup. 75 would be better.

[Maverik]

Have an idea of your brake line pressures? Hopefully someone should, then figure out the pedal ratio and you can figure out the load exerted by the driver to attain the pressure (for a given master cylinder size, etc...) simple fluids and statics. If you are designing from the ground up, figure out what pressures you want in the brake calipers, then the size of masters, and then define your pedal ratio to what you want to exert.

[markocosic]

I'm working on 300N/g (~60lb/g) pedal force gain.

You might want to look at:

NHTSA pdeal force gain data, Gillepsie, Fundamentals of Vehicle Dynamics, SAE, ISBN 1-56091-199-9, pp74

And also the velocity-time data published courtesy of Honda/Leeds Uni/Oxford Brookes which will show typical accel and decel around the track for an FS car. Linearise it all, calculate the decelerations, throw in a pedal force gain and out will pop your brake pedal pressure during typical brakign manouvres, average this, find out what your drivers like to see as an average brakign decel (or better still, I'd love to see data as to how well they can control brake pressure at different loads for a given seating position), then do your goal-seek to choose pedal ratio.

Sanity check it by reverse engineering a few established designs and seeing where they ended up?

[adfec]

Thanks markocosic for the ref.

Be sure I'll take a good look

Adam

[Kurt Bilinski]

I'd think you want it as light as possible, balanced against the inevitable compliances working against you. That is, if you can lock the tires with, oh, 50lbs, wouldn't that be a better deal? How about 30lbs? Even better. The trouble's going to be the compliances of all the brake components using up your pedal stroke. Until I got rid of caliper flex in my Mini, I had to use a larger master cylinder just so I wouldn't use up all the pedal travel. Now, with rigid calipers and a hard pedal, I was able to go to a smaller master cylinder and got the pedal pressure way down.

[Brian Evans]

You basically want a hard firm pedal with minimal movement because your brain finds that easy to control. As far as pedal pressures are concered, can you stand on your toes on one leg? If you can, your ankle/calf can handle pedal pressures equivalent to your weight, at least.

Brian

[mtg]

When you make the pedal force really low, your ability to modulate the brakes goes away, making it more difficult to trail brake. We experimented with brake pedal force when I was in school and I liked 100lb/g much more than 60 lb/g because I could trailbrake like a MF much easier.

[Kurt Bilinski]

I didn't know MFers were good trailbrakers http://fsae.com/groupee_common/emoticons/icon_wink.gif Anyhow, yes, I was assuming that regardless of the force you end up with, you want a rock hard pedal. Having a squishy pedal does really bad things to your confidence when heading into corners. It did to me.

[Steve Yao]

As aluded to earlier, your driver positioning should be taken into account as well. (Straight, vs bent, vs semi-bent legs). I bring it up mainly to point out that the weight of the driver's leg can have a part to play as well.

Say your a driver's leg weighs 30lb. from toe to mid thigh. At 1.5G braking, the leg mass itself is providing 45lb of pedal force. I've heard of F1 drivers being able to brake one leg in race, but need to 2-foot the pedal to stop in the pits. That had to do with aero effect allowing 4+G braking on track, but half that at pit speed.

So don't assume the bathroom scale to the wall will get the best target. I've been using ~85lb/G which leads to ~150lb for lock-up... at least on our practice lot.