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Old 08-13-2012, 04:47 AM   #211
JRWooden
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Thanks Jon!
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Old 08-13-2012, 10:30 AM   #212
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Originally Posted by Jon_PDX View Post
So in non technical terms, instead of one ABS control valve per wheel there are two valves....Either way (1 or 2 channel) the ABS will only activate on the wheel that locks and not effect braking on the wheel that has not locked.
I'm not so sure. While they do mention two valves in proximity to the discussion of two-channels, it may really just be conicidence. This is a very poorly written document and is really talking about ABS and CBS together, not about ABS systems in general.

Here are some other quotes from Wiki and others. Granted, these are mostly about car systems. But the general consensus seems to be that "channels" refers to number of independent hydraulic circuits that can be controlled by the ABS computer:

================

Anti-lock braking systems use different schemes depending on the type of brakes in use. They can be differentiated by the number of channels: that is, how many valves that are individually controlled—and the number of speed sensors.[15]

Four-channel, four-sensor ABS
This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.
Three-channel, four-sensor ABS
There is a speed sensor on all four wheels and a separate valve for each of the front wheels, but only one valve for both of the rear wheels.
Three-channel, three-sensor ABS
This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle. This sys*tem provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness. This system is easy to identify, as there are no individual speed sensors for the rear wheels.
One-channel, one-sensor ABS
This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle. This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness. This system is also easy to identify, as there are no individual speed sensors for any of the wheels.

============

ABS comes in about 4 different flavors:

1 or 2 Channel 2-wheel (Rear ABS) - This ABS is usually prevalent on trucks. It consists of 2 ABS sensors on the rear wheels and one or two ABS channels to pulse the rear wheel together (1 channel) or separately (2 channels).
2 Channel 4-wheel Criss-cross - This is the ABS system present on the 91-94 Sentra. It consists of 4 ABS sensors (one on each wheel) and 2 ABS channels arranged in a Criss-cross (Left Front & Right Rear, Right Front & Left Rear). When the right rear wheel locks up, the left front wheel & right rear wheel are pulsed together.
3 Channel 4-wheel - This is the more common ABS system in cars. It consists of 4 wheel sensors and 2 channels in the front (LF, RF) and one channel for the rear wheels. When one of the front wheels locks up, it pulses independently of the other wheels. When one of the rear wheels locks up, it is pulsed together with the other rear wheel, similar to a very fast pulling and releasing of the emergency brake.
4 Channel 4-wheel - This is the ABS system present on the 95+ 200SX/Sentra. It consists of 4 ABS sensors and 4 ABS channels. All wheels pulse independently of each other, like it should be.

===============

I honestly don't know. It is a bit amazing to me that there doesn't seem to be any documents on the net that clearly explain such basic concepts.

- Mark
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Old 08-14-2012, 08:05 AM   #213
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Mark,

I know what you mean. I looked at the Wiki page and got really confused trying to apply what they were saying about cars to motorcycles. So I kept looking and found the motorcycle related one which included the diagram I posted that made a lot more sense......to me.

I think where it gets confusing is on a car you have one peddle that works the brakes and on a motorcycle (without linked brakes) you have independent control of the front and rear brakes.

So in a car the best setup on the Wiki page would be a 4-channel design. Carrying that over to motorcycles, since we only have two wheels then we have a single channel per wheel which is how the 4-channel car setup is.

In the 2-channel motorcycle design in the diagram it's 2-channels (control valves) per wheel.

I think they, the motorcycle industry, have confused it by using the same term (channels).

To make it more confusing.... on the motorcycle it appears they are calling the control valves the channels but on the car they are calling the wheel sensors the channels.

I'm really tired from working all night so I hope I made sense

Your guess is as good as mine if that setup is really better, or even needed. But I suspect it will attract more customers because it sure sounds like it's better.

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Old 08-14-2012, 08:06 AM   #214
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Quote:
Originally Posted by JRWooden View Post
Thanks Jon!
You're welcome.
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Old 08-14-2012, 08:38 AM   #215
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Quote:
Originally Posted by Jon_PDX View Post
I'm really tired from working all night so I hope I made sense

Your guess is as good as mine if that setup is really better, or even needed. But I suspect it will attract more customers because it sure sounds like it's better.
Yes, you made perfect sense. Maybe you're right, channels on a bike aren't the same as channels on a car. I certainly would hope you get independent braking of each wheel on almost any motorcycle system, but things do seem ambiguous.

Someone mentioned testing it out. That's surprisingly difficult. Bringing either end of the bike to lockup individually is certainly doable - I've done it testing ABS many times - but when the ABS system works, there is no way to tell if it is releasing the other wheel since you're not braking on that wheel. So, instead you have to brake reasonably hard on both wheels, and then bring one to lockup, trying to sense if it keeps braking on the other while it's cycling on/off several times a second. That sounds tough to me.

I will also mention that I had an early R1100S ABS for many years and this was one bike where sportbike riders would bitterly complain about how the bike would "freewheel" into bumpy corners on stutter-step pavement. You occasionally hear about this on other ABS bikes. This sure sounds like a a scenario where during hard braking over bumps with the back end light, it locks up the rear brake all too easily and then it releases both brakes. I don't recall having much problem with this, but in hard riding, I'm pretty much brake only on the front and the front likely doesn't reach ABS lockup nearly as easily. If my theory is correct, then I think this is another reason to try and wean riders away from relying so much on the rear brake - when I was MSF teaching experienced students, overuse of the rear brake was one of the most common bad habits I saw. (I have a S10 and a S1000RR now - both I think have relatively sophisticated ABS systems I hope - and both have CBS also. I don't try and outguess the system in normal riding and just use the front brake lever nearly all the time.)

Related, I've always wondered how a motorcycle system works with respect to relative speed sensing between the two wheels and absolute speed sensing on each individual wheel. If both wheels are starting to lock, then relative speeds seem of little use, so how does the system know enough about traction conditions to decide what an acceptable and unacceptable rate of absolute deceleration is in each wheel?

Again, just surprised how much marketing crap there is out on the net about these systems yet very little hard information about how they fundamentally work.

- Mark

markjenn screwed with this post 08-14-2012 at 08:44 AM
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Old 08-15-2012, 02:57 AM   #216
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Quote:
Originally Posted by JRWooden View Post
Reading the August BMW MOA article on the new F700GS/F800GS it's not very long ... but it does say:

"both have the new 2-channel ABS for the first time" ....

Can someone explain or point me to an explanation of how this is better?

As a point of interest it claims "road ready" weights of 471lbs / 460lbs
Quote:
Originally Posted by markjenn View Post
I'm not an expert, but I think the number of channels refers to whether the ABS system has independent control of each wheel. On a motorcycle, a 1-channel system would, after sensing lockup, release both brakes. A 2-channel system can modulate each wheel independently. I know this is the sort of terminology used on cars where 4-channel systems are now common.

But I'm a bit surprised they're only now putting a 2-channel system on this bike.

- Mark
Ah ha......check this out.

From this article...
http://www.asphaltandrubber.com/news...bs-safety-360/

The advent of dual-channel ABS has allowed the rear and front wheels of a motorcycle to be modulated independently, a boon for using ABS in off-road applications where locking up the rear tire is still a predominant motorcycle riding technique. Allowing riders to lock up the rear tire while modulating the front brings the best of both worlds of braking power and motorcycle control — especially during panic situations.

And from this article...
http://3d-car-shows.com/2012/the-bmw...ntrol-systems/

ABS for the entry level and medium category.


An ABS was likewise introduced in the entry-level model F 650 GS
(single-cylinder) in the year 2000. This is a solution specific to the segment: a compact, light (2.1 kg) dual channel valve system without integral function.


A refined system on this basis was used from 2006 in the medium category models of the F series and in the sports boxer machine R 1200 S. The new generation of BMW Motorrad ABS is characterized not just by a compact structure and low weight (1.5 kg) but also by much improved control quality as compared to the predecessor generation.

In 2008 the system was slightly modified, with braking distances shortened even further by means of an improved lift detection function for the rear wheel and extended diagnostics.

In 2009 the system was then further optimized with the addition of a new pressure sensor for the launch of the BMW F 800 R – to match the sporting purpose for which the roadster was designed.

Based on the BMW Motorrad principle “Safety 360°”, the latest generation of the BMW Motorrad dual channel ABS will be installed for the first time in serial production from model year 2013 in the two new models BMW F 700 GS and F 800 GS. The new system is not only much lighter, weighing just 700 grams, but is also more compact in size that the previous generation. What is more, it now has inlet valves which can be infinitely adjusted for an even better response. New wheel sensors automatically monitor the distance between sensor and sensor wheel. As usual, the new standard ABS can be deactivated at the press of the button if the rider so wishes – for example for active riding over rough terrain.

-------------

If I read the comments in the second article correctly then it's been dual channel since at least model year 2000 but they have improved it for the 2013 model year.

Did you notice I even kept this on topic by quoting something that mentions the 2013 F700 and F800

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Old 08-15-2012, 03:10 AM   #217
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Originally Posted by markjenn View Post
Yes, you made perfect sense. Maybe you're right, channels on a bike aren't the same as channels on a car. I certainly would hope you get independent braking of each wheel on almost any motorcycle system, but things do seem ambiguous.

Someone mentioned testing it out. That's surprisingly difficult. Bringing either end of the bike to lockup individually is certainly doable - I've done it testing ABS many times - but when the ABS system works, there is no way to tell if it is releasing the other wheel since you're not braking on that wheel. So, instead you have to brake reasonably hard on both wheels, and then bring one to lockup, trying to sense if it keeps braking on the other while it's cycling on/off several times a second. That sounds tough to me.
Glad I made sense

That was me that mentioned testing it out. You bring up some interesting points. I'm not sure if I'm up to risking my bike but.... do you think this could be safely tested on a dirt or lightly graveled road on a slight down hill? If so I might be up to trying to engage the rear abs and using some front at the same time to see what happens. For sure it should be safer (???) than trying it on pavement.
Of course if someone else would rather do the testing I'm ok with that

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Old 08-15-2012, 06:32 AM   #218
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So on the new models can we expect the ABS-button to have 3 settings:
ABS-on
ABS-off
ABS-on for front wheel only
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Old 08-15-2012, 08:13 AM   #219
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Quote:
Originally Posted by JRWooden View Post
So on the new models can we expect the ABS-button to have 3 settings:
ABS-on
ABS-off
ABS-on for front wheel only

Ok I've heard the front only ABS talked about over and over and over.

Just from a technical point, How could this happen?

(correct me is I missed something)

ABS works by sensing wheel speed, it relieves the braking pressure on the wheel that is slower (because it is locking up)

if you lock the rear wheel up to slide it, what is it going to use to detect the front is locking up or just coming to a stop?
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Old 08-15-2012, 12:24 PM   #220
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Originally Posted by machinebuilder View Post
Ok I've heard the front only ABS talked about over and over and over.

Just from a technical point, How could this happen?

(correct me is I missed something)

ABS works by sensing wheel speed, it relieves the braking pressure on the wheel that is slower (because it is locking up)

if you lock the rear wheel up to slide it, what is it going to use to detect the front is locking up or just coming to a stop?

Hmm That is a good question....

I'm fairly sure that there are bikes that can do thsi from the factory, but not for sure.

I would think it could be achieved by using the front wheel speed sensor, and not applying the brakes if the wheel is stopped, if it is getting no movement from the rear speed sensor.

Since the rear brake is locked up, if you were at a stop, that would hold you in place (not always depending on hills etc) and then the system could release the front brake until it starts to move again....

I'm not a brake engineer, but it seems like it could be accomplished...

Ryan
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Old 08-15-2012, 12:41 PM   #221
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Great Discussion, How Does it Change Riding the Bike

You guys are way smarter than me, but how does this matter when we are braking?
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Old 08-15-2012, 01:37 PM   #222
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... if you lock the rear wheel up to slide it, what is it going to use to detect the front is locking up or just coming to a stop?
That is an excellent question ...

I have some ideas but I'm not sure any of them would be practical ... in an era where everyone is walking around lawyered-up ....
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Old 08-15-2012, 01:40 PM   #223
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You guys are way smarter than me, but how does this matter when we are braking?
Go to a nice level gravel area and do some braking practice

1st. leave ABS on and grab all the brake it will let you (front and rear)
2nd. turn your ABS off and lock the rear tire, while threshold braking with the front (just shy of locking it up)

Oh be careful with #2, or you will practice picking the bike up


Which stops you faster.

All this is irrelevant to me as I have one of the few F8's without ABS, it just makes for interesting reading and discussion.

I personally don't like ABS on cars, or trucks, when the road is in bad shape (dirt, ice, snow, etc) i have slid much further with ABS than without. The more important thing is to stay within the limits and know how your vehicle is going to react.
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Old 08-15-2012, 02:18 PM   #224
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Originally Posted by Dano7619 View Post
You guys are way smarter than me, but how does this matter when we are braking?
I think it is mostly of academic interest and just, in general, knowing your machine strengths and weaknesses. Might alter your evaluation of whether you want ABS or think it is worth the money. And, as I mentioned earlier, I think avoiding rear braking in bumpy conditions may be warranted on early ABS bikes where minor ABS engagement in the rear can take away most of your stopping power on the front.

- Mark
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Old 08-15-2012, 08:45 PM   #225
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Originally Posted by Dano7619 View Post
You guys are way smarter than me, but how does this matter when we are braking?

I have 20k miles ish on my 800, and my rear abs sensor has been broken for the last 10k so I currently have a no abs bike.

I ride my wifes 650 twin a fair bit which has functioning abs.

It works well, even off road. I have had very few offroad situations where I wish I had turned it off, loose gravel and steep downhills seem to be the main culprits.

I really like to skid the back tire on corners, probably just because its fun.

It would be nice to be able to grab a handfull of front brake ,abs on, essentially braking on the threshold of a skid, and also be able to skid the rear. This can kind of be accomplished by downshifting, but as soon as you are mid skid, that seems to be the time that your RPMs catch up, and your rear abs engages, and you almost high-side!!

Ryan
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