On wet roads, a cyclist is at a natural disadvantage if hard braking is required. ABS would help to minimise this problem, and could be implemented as below:
Hall effect speed sensors (like current cycle computers) on both wheels would allow bicycle speed to be detected during normal riding. On application of the brakes, a set of solid-state accelerometers would measure the deceleration of the bike and compare it to the wheel speed. If a wheel was found to be stationary when the bike was still decelerating, an actuator would slacken the brake cable just enough to restore movement and then re-apply the brakes, much as a car's ABS operates.
Under conditions of power loss (flat battery) the actuator would assume a fail-safe position. As the actuators would be the only moving parts, useful battery life should be available from a relatively small pack.
[edited to reflect the fact that I need accelerometers, not gyros, for this to work. It's deceleration we're trying to measure, after all]-- david_scothern, Sep 09 2006 It sounds good, and would prevent a lot of accidents. Few people can properly brake a bicycle. Hmm, they'd still need to learn how to do it right, but this would make it easier. If this is too expensive to fit on all bikes, put it on a few training bikes and sell braking lessons (not that the people who need the training would bother).
When I was riding a fixed-gear bike, I found that I could stand up and stiffen my legs just right, and get the back wheel to skid and catch just like an ABS brake, and control braking by moving my weight back. That worked better on wet roads, but it got me looking at ways to put ABS on bikes, and considering the importance of doing so. Congrats on figuring out a way.-- baconbrain, Sep 09 2006 Happily, fine precision from the accelerometers is unnecessary. They just have to determine if, given the decelerations experienced, the wheels should be stationary or not. A margin of error of a few miles per hour would, at worst, cause the brakes to release momentarily when the bike is stationary with them on, as the system thinks that it should still be doing 5mph. For determining lockup at 20mph it should work very well.-- david_scothern, Sep 09 2006 The benefit of ABS is the pulse, right? They do not lock. One could do this mechanically by making the wheel rim (where the brakes contact) into a series of slopes. The pad would hop off one slope and land on the next - within a fraction of a second, but fast enough to keep it from locking.-- bungston, Sep 09 2006 The benefit of ABS is that lockup is sensed immediately and counteracted. The most effective braking occurs when the car's brake pedal is depressed hard, but not quite hard enough to lock the wheels and force the ABS to kick in. When you feel your ABS turn on, back off on the pedal just a little; you'll stop faster that way.-- david_scothern, Sep 09 2006 Adventuresome feeling, hanging on an Idea that still has a long way to go.-- reensure, Sep 10 2006 Yep, the idea is pretty good but I just like the skidding too much.-- zeno, Sep 10 2006 Some friends of mine and I did this about 10 years ago as a engineering course project. It worked OK, but there were some issues. You actually don't need the accelerometers, just the Hall effect sensors on the wheels (we found 4-8 per wheel worked well). You can compute the speed by counting sensors, and there are a number of logic operators you can use to determine if the bike is still moving once the ABS is engaged (For example IF(the brakes are open AND no Hall sensors detected for 5 seconds) THEN(Bike is stopped)). The really tricky bit is the actuator. We used a direct screw drive attached to a servo to slacken the cable. This worked very well. The problem came when tightening the cable. With a direct screw drive you had to keep pulling, which drained the battery very quickly. Some kind of ratcheting mechanism, or better yet a hydraulic brake system with a check valve and pump would work better. You'll still have problems with battery life because the battery has to source power to do mechanical work, not just shuttle electrons around. You'll need something akin to a cordless drill battery, rather than a laptop battery, with the associated weight.
Happy Baking-- ks#, Sep 12 2006 Overly complicated. Learn to keep control in a skid, it's not that hard and you can make it look really cool.-- GutPunchLullabies, Sep 12 2006 //The benefit of ABS is that lockup is sensed immediately and counteracted.//
This is correct.
// The most effective braking occurs when the car's brake pedal is depressed hard, but not quite hard enough to lock the wheels and force the ABS to kick in. When you feel your ABS turn on, back off on the pedal just a little; you'll stop faster that way.//
This however is incorrect, The fastest way to stop an ABS equipped vehicle is to slam the brakes as hard as you can and hold them there. The ABS will modulate the brake pressure only enough to keep the wheels from stopping. It can do this with a far greater degree of control than any normal driver can match and so will maximize the amount of braking force that can be applied to all the wheels independently in near realtime. Inside it may feel like the brakes are not working well but outside they are literally working to their maximum potential.
In a nonABS equipped vehicle this would be the correct procedure(IE in heavy trucks this happens regularly)
As to the main idea I dont know how well a mechanical system would work, Hydraulic works well because the changes in pressure can be actuated by a minutely small change in overall system volume, which allows for extremely high speed response. A disc brake system would be preferable at which point a basic sensor can be built into the brake caliper and brake disc. No accelerometers would be needed as the only required input is RPMS of the wheel(this is how all conventional systems operate)-- jhomrighaus, Sep 12 2006 I'd debate the "no accelerometers" bit; if you locked up both wheels the system might well think you were stationary. The accelerometers are there to tell it otherwise.
Nice to see that it's been done (and without the accelerometers, I note).-- david_scothern, Sep 13 2006 //The fastest way to stop an ABS equipped vehicle is to slam the brakes as hard as you can and hold them there.//
Incorrect. In an emergency situation where you panic and just stomp the brakes, ABS is better than lockup, as it allows you to retain some steering control. It does NOT help you stop more quickly. The fastest stops are performed with threshold braking, where the brake pressure is maintained just shy of the lockup point.
Every car that I've ever driven in conditions where the ABS could be tested decelerates hardest just prior to abs activation, with a noticeable reduction in braking performance while the ABS is doing its job.
Unfortunately, manual threshold braking is a real skill that very few people take the time and effort to master to the point that it comes naturally even during a panic stop.
Active stability control, on the other hand, can be very beneficial in emergency braking, as it modulates each brake independently to keep the car pointed in the right direction.-- Freefall, Sep 13 2006 Huh? Never needed this. How/what do you guys ride? Going 60mph on ultrathin tires? Rear wheel skids don't really upset the balance that much. You can come to a hotdogging skidding stop while standing up or sitting down, or let off a little and save your tires.
Bicycles with drum brakes: brake with mostly front brake. Bicycles with reverse brake, see above. Bikes with rim brakes: well those brakes don't really work in the rain, do they? Bikes with disc brakes: never rode one, but I would think it's like drum brakes, but better. Brake with mostly front brakes. Bikes without brakes: not an issue.
I agree with [GutPunchLullabies]-- jmvw, Sep 13 2006 Would all the professional racecar and test drivers who have sufficient experience to correctly perform Threshold braking consistently in a variety of nontrack related environments please raise thier hands!
Anyone?
Anyone at all?
I didnt think so. I stand by my statement that the best way to stop an ABS equipped vehicle is to stand on the brakes and pay attention to steering the car. If you look on line you will find that "highly experienced, highly skilled drivers driving vehicles with highly developed braking systems(Sports Cars) can match or SLIGHTLY decrease stopping distance compared to similar ABS equipped vehicles".
If Joe Driver follows your advice he will be significatly increasing his stopping distance over what the ABS would do on its own.
For mere mortals driving normal automobiles, threshold braking is simply not achievable, where as ABS works every time.-- jhomrighaus, Sep 13 2006 + I was told to mash down on brakes w/ ABS. While, I am not a professionally trained driver, I got a lot of experience on many different road conditions when I first started out driving by delivering pizzas in the Midwest. (rain,snow,ice,gravel) I was able to pulse the break (hard, not as hard, hard, not as hard....) in order to keep from skidding, but I don't think I could stop a car that way faster than ABS would - I've had to hard stop with both and was amazed with ABS the first time I had to use it (I knew I was going to get crushed by a fire truck, but was able to stop short).
I used the same pulse technique (though I think only with the front brake, it's been a while) when riding a bike for quick stops & again think that ABS would work better.-- Zimmy, Sep 13 2006 I wonder if you could do this mechanically without requiring a battery operated actuator. A little wheel running just in front of or behind the brake pad. This wheel rides on the rim slightly before the brake is engaged. As long as it is turning, it maintains a little extra tension on the brake/cable, bringing the pad into contact with the wheel. As soon as the wheel stops turning it releases this tension and the brake backs off a bit.-- MechE, Aug 15 2008 random, halfbakery