Anti-Lock Brakes For Bike Might Make Rides A Little Safer

Crashing one’s bike is a childhood rite of passage, one that can teach valuable lessons in applied physics. Assuming the kid is properly protected and the crash is fairly tame, scrapes and bruises are exchanged for the wisdom to avoid sand and gravel patches, and how to avoid a ballistic dismount by not applying the front brakes harder than or before the rear brakes.

But for many of us, those lessons were learned long ago using a body far more flexible than the version we’re currently in, and the stakes are higher for a bike ride that includes braking mistakes. To help with that, [Tom Stanton] has been working on anti-lock brakes for bicycles, and in the process he’s learned a lot about the physics and engineering of controlled deceleration.

It seems a simple concept – use a sensor to detect when a wheel is slipping due to decreased friction between the tire and the roadway, and release braking force repeatedly through an actuator to allow the driver or rider to maintain control while stopping. But that abstracts away a ton of detail, which [Tom] quickly got bogged down in. With a photosensor on the front wheel and a stepper motor to override brake lever inputs, he was able to modulate the braking force, but not with the responsiveness needed to maintain control. Several iterations later, [Tom] hit on the right combination of sensors, actuators, and algorithms to make a decent bike ABS system. The video below has all the details of the build and testing.

[Tom] admits bike ABS isn’t much of an innovation. We even covered an Arduino-instrumented bike that was to be an ABS testbed a few years back. But it’s still cool to see how much goes into anti-lock systems.

59 thoughts on “Anti-Lock Brakes For Bike Might Make Rides A Little Safer

  1. It all started with trebuchets. I also sent a tip in, but I figured you guys are just subscribed to his channel and I will see an article in a couple of days ;).

    It’s good work he is doing though I think that some PID control can help out the project or have the controller provide an intial input based on the brake handle being pressed and damp that input before trying to damp it after it’s already clamped down.

  2. I admire his inquisitiveness and ability to put time and resources into a project that, although is a great learning experience, stands a good chance of being pointless. Wish I had that kind of time.
    I would say though, that the number of reflectors he has on his wheel is really to low of a sampling rate for a low speed vehicle like a bicycle. ABS needs more resolution to start with in order to work up faster reactions.

    “and how to avoid a ballistic dismount by not applying the front brakes harder than or before the rear brakes.”
    Yeah, ahhh, no. Just no. That’s just a recipe for not stopping quick enough to avoid the thing you’re trying to avoid. 80 percent front, 20 percent back. The front wheel is your friend in dire straits. Learn to use it properly. If you rag doll over the handlebars, you’re not planning far enough ahead, or you’re not shifting your weight back far enough. Or a squirrel just tried to jump through your front wheel spokes.
    Not much you can do about that last one.

    1. Don’t think the reflectors were for the sampling – he has a 3d printed encoder wheel on the hub itself with a decently high resolution. The reflectors were more likely for showing the wheel spinning for Youtube viewers / easier speed calculations in post processing frame analysis.

      1. I’d like to see him test the system with proper braking technique. Butt hovering off the saddle, arms outstretched to keep more weight over the rear wheel. Guarantee you an experienced rider will be able to stop in a shorter distance without this system.

  3. I just read that topic like 10 times.
    Its like a damn tongue twister…

    Neat idea though. Yet, the stepper seems to be a little slow for the work.
    He needs a strong solenoid in my opinion, so it can be controlled much faster.

  4. Maybe a similar thing would be possible using ebike front motor. Instead of decreasing brake power, briefly increase motor power if the wheel starts to slip.

    Though most of the actual falls I’ve had due to front wheel lock have involved bike tilting so much that the side forces were too much to stop even after front brake was released. To avoid that, there would have to be some kind of a sensor that detects the slip even before it happens.

    1. Airbags prevent fatalities, not road-rash. And we don’t use parachutes on most planes.

      Whilst frozen rabbit is probably overreacting, there’s evidence to suggest that ABS etc. makes people worse drivers as it hides from you how close you are to losing control, and thus may increase risky driving, with an increase in fatalities when you reach a situation ABS can’t handle.
      Personally I’m glad to have it. But the argument has some weight and is being investigated. Cf also the affects of increased road safety signs and rules on drivers’ abilities to decide how fast is safe themselves.

      1. Partially right. There’s very little evidence ABS makes people riskier drivers. There’s some evidence that ABS increases some crash types. It’s an assumption that this must be because of riskier behaviour. ABS never hides how close you are to losing control – in fact it lets out a very disconcerting noise and pulsing sensation which sometimes makes people inappropriately release the brakes. It’s equally if not more likely that by making the vehicle more controllable, it allows it to react accurately to panic steering by the driver – resulting in swerving into traffic, rollovers and collisions with roadside obstacles – instead of straight line skidding.

    2. And in this case, learning not to go over the front wheel when stoping is as simple as relying primarily on the back brake, which every kid manages fine, so ABS on bikes is total overkill.

      Amazing build, nonetheless, I’d have not expected that to be possible.

      If we were looking for a solution to accidental over-the-front dismounts, surely there’s a simpler purely solution that would ensure that the rear brake always got more pressure than the front?

      1. Here’s a quick way to look at this: when you hit the front brake hard enough that the rear wheel comes off the ground, the rear brake effectiveness at that point is 0. The same holds for the whole braking process: you _have_ to rely on the front brake for most of the braking power, but you have to modulate it just enough that you don’t flip. I’m a bike racer, and in a bike race or any place where you suddenly need to stop as quickly as possible, you routinely see rear wheels slide and lift because the riders are at exactly their maximum braking effectiveness, and that’s where your rear wheel has virtually zero contribution to that effectiveness.

  5. If you use hydraulic brakes, would it not be much easyer, safer and a lot faster to have a piston based system (just take another break lever and hack that up into the existing system, that already gives you a piston rated for the pressures and fluids involved) that could regulate the volume in the hydraulic system and with that regulate the brake force?
    Anyway, i actually still prefer to have no ABS on the bike, just because it’s another point of failure in your safety system. If the ABS is going crazy and prevents you from braking at all, the accident might actually get even worse.

      1. Indeed many car systems go crazy when having “fun” on dirt roads and somehow really reduce – thats right, reduce the max braking forces to a point It feels like the brakes have totally failed. You get a mild slowdown of say 25% force. A disaster should you slide through a corner to find a tree across the track. Or turn off that scenic road to pull over at a gravel viewing platform but the brakes went nuts and you smack head on into the parking railing … I really cant figure out the reasons for it other than having all the wheels encounter varying levels of slip causes the slip ratio calculations to fail thinking we are all locked up so they back off the braking which you have only started to apply so they were basically barely on. No matter how hard you try to stomp on the pedal the system wont let you. Hmmm it’s possible but bloody dangerous and there is no off button.

      2. Guess since it DIY you can add a switch for those times though my biggest gripe is the use of an optical tone wheel vs magnetic.
        Open optical sensors and vehicles don’t play nice together.

    1. Yep. Go hydraulic just like on motorcycles. And while you are at it use motorcycle ABS pickup rings and inductive sensors. Open optical and vehicles don’t mix.

      Though charging your bike to just have abs is kind of silly. I suppose you could put in a hub motor and tie that into the brakes for regen braking to charge the abs battery.

      1. I was thinking the same thing as optical sensors are a bad choice for something that’s going to be exposed to water and mud.
        Another solution might be to use a reluctor wheel and an engine crank trigger sensor.

  6. so:

    What is the probability of the ABS system preventing harm?

    How much would the prevented harm cost?

    What is the probability that the ABS system malfunctions and causes harm?

    How much does such a system cost?

    Then we can think about if it’s worth implementing (given that different people will put different costs and harm and the future value of the money saved by not paying ahead of time to prevent harm)

    It’s always possible to be safer, however it’s not always practical or efficient to be safer.

    1. You really should take that strobe idea out of your survey.
      Go to a club with some strobe lights and try to cross the room at a fast pace, like jogging speed.. When you get through running into those people, you’ll have a mild idea of why a strobe light on the bike just makes things worse.
      That freeze/flicker effect screws with your eyes and makes it harder to gauge how fast you’re closing on the bike.
      Ask yourself why so many police are getting hit while standing near those very bright, harsh modern strobes (enough to need an ad campaign now) , yet we rarely heard of it before them?

      1. Here here on the disco lighting idea. Just get auto-motorcycle level of lighting with LED’s not those tiny trinkets running on tablet cells. 1100 lumin on front, working on the rear lighting. I wear a rear-vue mirror though, best safety gear by far.

        Hand brakes on a bike are already way better than using your foot, shorter nerve distance faster response time etc. I don’t know if this worth it at all. Only off road buggies and tractors have differential brakes, the rest of 4 wheelers get just one brake control hence ABS.

      2. Not to mention the risk of Target Acquisition, where a flashing light attracts a car/truck driver’s attention, particularly when DUI, when they look at, hence drive at, the flashing light and mow down the bike. Some jurisdictions ban flashing lights on bicycles to prevent this.

  7. I think it’s also plausible to build a mechanical version by using a centrifugal clutch with the disk brakes (like those inside some Yoyo’s. This way it’s not the brakes you need to control but rather the mechanical connection between the wheel and the disk brake itself. Springs can then be adjusted how much the clutch releases during sudden brakes.

    1. but you don’t want to release the brakes during all sudden stops, only when a wheel locks and you are still moving

      so you really need to compare the speed of all your wheels and only ease the brakes if one wheel stops while all the rest keep moving (in a bicycle you generally only have one other to reference, but the principal is the same no matter how many wheels you have)

      1. Ah yes, although he does explain that measuring both wheels on a bike aren’t ideal, compared to a car. I was kinda wondering this myself why he didn’t use this technique in the first place. The way his contraption works almost does the same thing as the clutch idea, and further improved by the accelerometer. He was looking for a trough in speed, which was what’s triggering the brake release.

        With the clutch, a sudden brake would cause it to release, and re-engage almost relatively as quick to how hard the sudden brake is. This would continue to gradually keep releasing and disengaging until the inertia isn’t able to release the clutch depending how hard you set the springs.

  8. Exactly.
    20 years back when I had a decent bike the brakes were so good I could stall the front wheel with 2 fingers.
    Made fun of that by putting my belly on the saddle (lower & further to the back center of gravity, and still braking so hard my back wheel lifted from the ground. I loved it.
    I would not tolerate a device like this where some hobby level hardware+sofware interferes with the braking ability of my bike. It’s ludicrous.

    Parachutes are fun.
    Airbags? Go watch some road rage on youtube and see how those can save your life from idiots.

    1. Hmm, maybe a device with imu, which could lock the brakes just enough so that you can lift back wheel a predefined amount? Auto-trick for bicycles? I think I’ve seen it somewhere already.

    2. Modern hydraulic brakes are so sensitive and efficient you can easily lockup with 1 finger. This was a neat experiment, but it’s a ridiculous weight penalty that takes control AWAY from the rider. It makes sense on a car where it’s a very heavy machine and people don’t have a good sense of what the conditions are at the tires. Also, feet aren’t super sensitive and the reaction time of your legs pumping a pedal isn’t anywhere close to what you can do with a finger on a lever.

    3. You’d love the modulation possible with more modern brakes.
      (And I made mine even better by limiting cable flex by running the sheathing inside copper tubbing…)

      And once someone rides with decent brakes and learns to module the braking force, there’s no need for an ABS system, let alone one that can’t pulse fast enough to do the job.

    1. for years I commuted an a classic car (with way to much power) and manual (non-servo, non ABS) brakes, the car could stop amazing when i was focused, but on a few occasions, say 2am on the way home from work, and i have to jump on the brakes I have locked up the front wheels, even a fraction of a second feels like an eternity, and by the time I have realized and let off a little to get back under control I have traveled much further than i’d like. Commuting in a modern car with ABS this scenario is much safer. no doubt.

      That said I have to disable traction control to get out of a jam in the winter and last year alone at least one decent pucker moment could have been avoided if I didnt have ABS trying to brake down a steep snow covered hill. While I appreciate you can drive better without it, for the day to day grind im sure glad it is there. even more so for those folks who dont “enjoy” driving.

      1. I have to turn off the TCS on my Corvette and GTP in winter as it’s useless on both cars in those conditions.
        At least GM had the foresight to provide a switch for this some manufactures won’t even do that.

  9. This seems unnecessary for hydraulic brakes, since there is often enough tactile user feedback in the levers to avoid locking the brake. Besides, this safety adds a very undesirable restriction on the rider: what about the cyclists who want to lock their front brakes?

    1. There could be enough feedback in the lever to allow a human to feel when the front wheel is about to skid commuting to work at 10mph. But going down a steep, rocky trail at warp speed on a mountain bike would be a different story.

      I think it would be simple to implement a feature that allowed the wheel to lock when the bike isn’t moving. But there is never a scenario where you want your front wheel to lock when the bike is in motion.

      This is a cool project though. Incidentally bike projects in the maker/hacker world always make me laugh a little because you end up with these “affordable” bikes with a bunch of fancy hardware strapped to them :)

        1. Common? That’s hilarious. I work in the mountain bike industry and have met maybe two people in my life who can actually do a real stoppie. I would estimate 0.05% of cyclists on earth can perform a stoppie. So no, that is not a legitimate concern.

          1. really? Most of my friends that rode when I was younger could – maybe coming from playing on BMX bikes learning tail-whip type things that require locking the front and balancing on it, but it wasn’t that uncommon… Heck, I’m over 30 and still can still make a ‘u-turn / 180’ in place by going up on the front end quick and swinging the back around on a MTB.
            – Very interesting learning project, but can’t say I actually see a market for it either. I wouldn’t see it having a place in the race or even just mid-upper MTB range, as either you’re into ultra-light or more budget prices, and either groups of riders could likely out-do an ABS system by hand anyway… And then getting into braking on loose surfaces in corners? – I’d rather not have a micro trying to handle my bike for me in a corner, when it doesn’t know the kinetics I’m planning by lean and whatnot (or how to miss that tree up ahead)… And lower MTB range wouldn’t want the excessive cost (likely?), even if the riders might benefit from it. Maybe in the ‘high-end comfort bike’ range, for riders lacking skill and having money to burn. I seem to remember some of those used to have an inline spring on the front brake cable to lower maximum force that could be applied, to keep (in most conditions) from being able to lock the front wheel (at expense of max braking force).

  10. I posted about this in a comment but I don’t know if it came through. So: people interested in simple, robust, lightweight, all-mechanical ABS might get a kick out of which Dunlop invented in the 1940’s and was being used on aircraft extensively throughout the 1950’s. It was single-use, requiring draining of a reservoir after the ABS ran, but it wouldn’t be hard to build a drainback from the ABS reservoir to the master cylinder reservoir.

  11. I will never go for a ride with anyone who has ABS on their bike. WOW. Learn to ride. The vast majority of biking accidents I have been in are from other idiots that do not know how to ride, and I do not want to be around idiots like that. I do not even want ABS in my car. My CRV is the first vehicle I ever had that has ABS. The first snow we got arfter getting the CRV, I got to the end of the block, the ABS kicked in at the stop sign, I made a loop around the block, pulled back into my driveway, and pulled the fuse for the ABS. It has been like that ever since. ABS is a crutch for Ignorance and I feel very strongly about it.

  12. A crutch? Maybe, but if it gets her out there having fun with you, it’s worth it! I made the mistake of teaching my lady how to first ride on an ATV (4 wheels), so she learned to grab the front brake good and hard. Unfortunately, her first unexpected and sudden stop on her new dirt motorcycle, and her hip hit a rock in the trail. She got back on, but was a lot more timid, and had a lot less fun. I think an improved version of this would have been great. Like the narrator said, inexperienced people could benefit, and sometimes it’s fun to share the time with inexperienced people.

  13. In its present form, it’s too slow cycling on/off to be an effective Anti-Lock. With that upgraded so it’s effective for what it is, and without needing expensive or heavy steppers, Anti-lock Brakes might have an application for Last-Mile delivery by (heavily loaded?) cargo bike (cargo-e-bike?).

    But I sure wouldn’t want anything messing with my control of my bicycle brakes. ABS works well on the van I drive though.

  14. What’s the point of this comment and the replies to it? Tom touches on this topic in the video and makes a case for where this might be useful. Aside from that, it was a fun and cool build.

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