Anti Lock Brakes

[langwadt]

I'd like to see a comparison of straight line braking distances with and without ABS. Last time I looked into it in a straight line a skilled, alert driver in a balanced car could beat the ABS, but since an ABS does your brake balancing for you, handles split mu, allows you to steer etc etc, in practice ABS was a better option most of the time.

You'll never get a straight answer on this from the safety nannies.

On the track ABS is usually seen as an advantage.However for FSAE I tend to agree with Tim, it is an awful lot of work for very small gains.

Tommy - yes ABS tends to be understeer in general

I seem to remember the discussion around ABS from Le Mans mid 90's, some driver telling that a driver could resonably easily beat it on and single lap but doing every lap wasn't so easy

[tuj]

racing abs has gotten much much better since the 2nd generation systems of the 90's. Modulation is simply faster than a human can achieve threshold braking, not to mention it automatically compensates for front-rear bias continuous adjustment throughout the braking maneuver.

there is a reason abs is verboten in most racing series.

[g-force_addict]

Hi every one !!
I'm from India. Well ,currently I'm working on Anti lock brakes.I know that it helps in reducing braking distance,improves steering stability and much more.
But I wanted numbers for it to prove it to my team leader.Actually we have tyre data for coffecient of friction Vs slip ratio. That curve reaches a peak value and remains almost constant at that value. So while we are travelling longitudinally , ABS is not much of use .So now now I'm seeing the effects of ABS on lateral motion of vehicle.I want to see the influence of ABS on lateral force. But I'm not able to get as to how to quantify this influence . Tyre data we are having gives Lateral force vs slip angle only for zero slip ratio.(ie. for zero longitudinal force)
So is there any other way to measure the impact of ABS on lateral force ???

Thank you in advance

ABS is banned in F1 and most racing series.

So while we are travelling longitudinally , ABS is not much of use
WTF?
Of course ABS is helpful in a straight line!

As for lateral force Do you mean during trail braking?
If so just check the traction circle (actually an ellipse) for your tires and calculate the maximum cornering and braking forces.
Make sure you include braking weight transfer in your calculations.

BTW all traction circle charts or tables I've seen only reference force, not slip angle.

[riff_raff]

racing abs has gotten much much better since the 2nd generation systems of the 90's. Modulation is simply faster than a human can achieve threshold braking, not to mention it automatically compensates for front-rear bias continuous adjustment throughout the braking maneuver.

there is a reason abs is verboten in most racing series.

A bit OT, but if you've ever done a panic stop driving a car with ABS, you'll have noted that it feels a bit eerie. You stomp on the brake pedal as hard as you can while trying to steer the vehicle in a safe direction. What you feel is the brake pedal pulsating at high frequency as the ABS system modulates the hydraulic pressure applied to each brake caliper to keep the wheels from skidding. Very unusual.

[Greg Locock]

Frankly, when the electronics takes over an experienced driver will always experience a bit of WTF. Personally I love it when the ESC kicks in on a gravel road and turns the steering wheel into a yaw input device.

[strad]

I still remember two things about active handling aids
1. When Heinz Harald Frentzen (I believe it was he) took the reporters on a lap around the new Indy F1 track and promptly spun off in turn two or three. Before the car had stopped he was saying "that was the car not me". The active handling aids in the Mercedes had caught him out.
2 A special on how the Audi system worked on icy roads. They drove to a frozen over lake on roads littered with cars in the ditch. Audi's test driver said.. " if you can drive, unlike those we saw on the way here, you have no use for it"

[langwadt]

racing abs has gotten much much better since the 2nd generation systems of the 90's. Modulation is simply faster than a human can achieve threshold braking, not to mention it automatically compensates for front-rear bias continuous adjustment throughout the braking maneuver.

there is a reason abs is verboten in most racing series.

A bit OT, but if you've ever done a panic stop driving a car with ABS, you'll have noted that it feels a bit eerie. You stomp on the brake pedal as hard as you can while trying to steer the vehicle in a safe direction. What you feel is the brake pedal pulsating at high frequency as the ABS system modulates the hydraulic pressure applied to each brake caliper to keep the wheels from skidding. Very unusual.

I believe that is why they came up with the system that will just keep the brakes fully on if the car thinks it is an emergency, because they noticed that people would slam on the brake and then "panic" and let go when the ABS kicked in

[riff_raff]

I believe that is why they came up with the system that will just keep the brakes fully on if the car thinks it is an emergency, because they noticed that people would slam on the brake and then "panic" and let go when the ABS kicked in

I believe many vehicles that have ABS and stability control systems actually use active braking of each wheel to correct the steering of the vehicle.

[Greg Locock]

correct

[Tommy Cookers]

A bit OT, but if you've ever done a panic stop driving a car with ABS, you'll have noted that it feels a bit eerie. You stomp on the brake pedal as hard as you can while trying to steer the vehicle in a safe direction. What you feel is the brake pedal pulsating at high frequency as the ABS system modulates the hydraulic pressure applied to each brake caliper to keep the wheels from skidding. Very unusual.

question - should this pedal pulsating be evident in current or recent cars ? (eg 4 year old Hyundai i10)
when I try to get this (as part of trying in the wet to make the ABS do something) there's no pulsating, the car just stops
the 'town car' static weight distribution driver-only must be about 70/30 (the real reason for ABS ?) so the rears should do something ?

[Blanchimont]

It depends on the system in use, but normally you should feel it and even hear it from the sound the tyres make. In (all?) BMW motorcycles the hand doesn't feel the pulsation because the brake system is decoupled from the hand lever when Anti Lock is active.

TC, did you really use all the force of your leg? Eg, in a VW Golf V, i had to use all the force, but in other cars Anti Lock kicked in earlier at a lower force on the pedal. I guess it depends on the brake booster of the car!

[Tommy Cookers]

most of the force, but that's not saying much
years ago (pre ABS) I did some braking tests in the dry and absolute maximum leg force could just start locking
about .8 g
anyway, I hear what you are saying

[Blanchimont]

Wait for the next snow or go to the nearest gravel road, the anti lock should work way earlier than on a wet road.

Or try to find out what kind of anti lock system your car actually uses!

[riff_raff]

TC-

If you stomp on the brake pedal with enough force to cause lock-up at any of the wheels, you should feel pulsations at the brake pedal as the ABS system bleeds hydraulic pressure applied to each brake caliper. Your car's brake circuit is hydrostatic, and has a fixed volume of fluid between the master cylinder and caliper cylinders once the brakes are applied. The ABS system works by bleeding a small amount of the fluid volume (and pressure) between the master cylinder and the individual wheel cylinder that it detects is beginning to skid. This high-frequency cyclic bleeding of fluid volume will cause a slight movement at the brake pedal every time it occurs, which is why you will feel pulsations of the pedal.

On a dry paved road surface you may also hear some "chirping" from the tires as they cyclically skid/roll/skid/roll when the ABS system does its thing.

[Cold Fussion]

A bit OT, but if you've ever done a panic stop driving a car with ABS, you'll have noted that it feels a bit eerie. You stomp on the brake pedal as hard as you can while trying to steer the vehicle in a safe direction. What you feel is the brake pedal pulsating at high frequency as the ABS system modulates the hydraulic pressure applied to each brake caliper to keep the wheels from skidding. Very unusual.

question - should this pedal pulsating be evident in current or recent cars ? (eg 4 year old Hyundai i10)
when I try to get this (as part of trying in the wet to make the ABS do something) there's no pulsating, the car just stops
the 'town car' static weight distribution driver-only must be about 70/30 (the real reason for ABS ?) so the rears should do something ?

In a Golf V R32 and a Meagane RS 265, the pulsating brake pedal under ABS is very evident, with the Golf system in particular feeling quite disconcerting. I would agree that ABS on a FSAE car is mostly a waste of time. You're better off using the wheel speed sensors to implement a traction control system, as that will at least net you some points in the acceleration tests (fly by wire throttles are allowed from 2015, at least in FSAE-A).