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toybuilder
03-15-2003, 06:55 PM
Hi gang,

I gave out an extended (1 hour) demo to a distinguished gentleman today, and in the course of Q&A, we talked about the fact that the Segway has no brakes.

It seems that one of the greatest fears of the Segway comes from the fact that the Segway technically has no brakes. This is my first attempt at explaining why the Segway is safe without brakes. Please give me your comments!



The Segway is safer for having no brakes.

That sounds weird, doesn't it?

Once upon a time, it was believed that an object made of metal couldn't fly. It was also once believed impossible for two people in two different cities to hold a conversation. But we know today that airplanes do fly, and telephones do allow distant conversations. The science didn't change. Instead, each of these invention broke the "rule" of contemporary thinking.

The Segway HT breaks the widely held belief that the only safe way to stop a moving vehicle is to apply a brake.

But wait a minute -- the human body doesn't have brakes. How does a person come to a stop? Well, if you pay attention to what your legs are doing, you'll noticed that you stop by applying force against the momentum of your travelling body. The effect is more noticeable when you try to stop while running, or if you repeatedly rock backwards and forwards (take two steps forward, two steps back). Your brain controls your legs to apply enough force to slow down the body until it comes to a complete stop. If that leg can't safely stop you on the first step, you take another step and continue to push back with the other leg. (If you tried to stop only on the first step, and didn't take the additional steps, you' end up falling flat on your face.)

The Segway essnetially does the same thing -- when you decide to stop, the Segway applies the right force against the momentum of your body to slow it down and come to a stop. It doesn't lock the wheel, or try to stop at the exact place you began stopping. Instead, the wheels continue to roll along while applying the force that slow you down.

A Segway stops in about the same distance as a person travelling at the same speed. If I'm going at a walking pace, I can stop in about 6 inches. If I'm going 12 mph, I need about 10 feet. 10 feet sounds like a lot, but a runner will also need 10 feet. Laws of physics can't be broken.

Of course, if all we wanted was to stop the Segway, a properly modulated "antilock" brake would probably work -- but there's an actual safety advantage to using the counter-force instead of brakes: you can go backwards.

When you're walking, and you suddenly encounter a danger, your first reaction is to stop. But you might actually want to move back away from the danger. When you're on your feet, you just pump your leg to carry you back a few steps. With the Segway, you let it roll you back a couple foot or so. Try that on a bicycle or a scooter!

http://www.pasadenasegway.com

Do not let yourself be forced into doing anything before you are ready.
— Wilbur Wright




John F
03-15-2003, 07:03 PM
Nice :)

Mail it in or post it up -- Segway-open mailing list on Yahoo Groups (http://groups.yahoo.com/group/segway-open/)

2totango
03-15-2003, 07:12 PM
Double nicely said. Well described and explained.

rbmartin
03-15-2003, 09:20 PM
The Segway doesn't have "brakes" per se, but it does have a "braking system".

It uses a technique called "dynamic braking" in which rather than driving the motors with electrical current, an electrical load is applied. This basically makes the motors very hard to turn and achieves the same thing a friction brake would, but without any mechanical wear and tear. This is not a new idea; diesel locomotives have used a similar system of braking for decades.

The current generated by the motor while braking can also be used to recharge the batteries. This is called "regenerative braking" and the Segway does this too. It increases the range somewhat.

In a sense, the Segway doesn't really try to stop you. You stop by shifting your weight and the Segway just works to stay underneath you :)

pt
03-15-2003, 09:30 PM
quote:Originally posted by toybuilder...and in the course of Q&A, we talked about the fact that the Segway has no brakes. The Segway is safer for having no brakes.

i wouldn't say that, it has a braking system. it doesn't have a "gas pedal" but it does accelerate. i would change the wording to "the segway has an intutive braking system" and not confuse anyone. when giving demos people rememer little bits "no brakes" isn't accurate, so i'd say "super-brakes" or something like that :-]

cheers,
pt

http://www.bookofseg.com

toybuilder
03-15-2003, 09:53 PM
Hmm, yeah, that's true -- it is a dynamic braking system. What I was trying is to make the point that the stopping system on the Segway (dynamic braking with battery power regeneration) is different from traditional mechanical friction braking.

It's the Segway's lack of mechanical brakes that seem to raise the objections, so I was writing to that audience.



http://www.pasadenasegway.com

Do not let yourself be forced into doing anything before you are ready.
— Wilbur Wright

pt
03-15-2003, 10:16 PM
i would just keep it simple out on context "no brakes" sounds bad and it's just not true. "dynamic braking" next generation braking systems on the segway ht, that' accurate (and cool).

cheers,
pt

http://www.bookofseg.com

dexter
03-23-2003, 11:03 AM
To someone who thinks the Segway doesn't have brakes, you could say that it does have brakes, it just doesn't have brake shoes.

I think another reason it is safer is that the braking system handles stopping both the Segway and the rider as a single entity. i.e. when you "brake" the Segway the system works intuitively to bring both the machine and the rider to a complete stop without either losing their balance. A mechanical brake could possibly end up throwing the rider off of the vehicle or at least causing loss of control, which is exactly what you don't want in an emergency situation. No need for seatbelts or magnetic gravity boots or anything to keep you on the machine during a sudden stop.

Peter iNova
03-23-2003, 02:37 PM
I see the problem. It's that you need a quick way to disentangle the notion of wheel-locking brakes--a thing cars have--from the notion of fast-stopping, which is what our HTs have. People tend to lock into what they've been aware of in the past as the ONE thing that fits their understanding of it in the present.

I have tried several ways to impart the idea and I see that getting into an involved discussion of regerative braking, dynamic braking, the motor becomes its own brake, and so on, is not helpful. It does help, however to start from the conceptually fixed (stopping power) and go to the moveable (the actual details of the system) as a building explanation using Power Assist mode as a teaching aid.

A: The brakes are huge, powerful. The whole wheel becomes the brakes.
B: Try pushing it in Power Assist mode with no power applied. See? The wheels are in a state of half-brake without anything else going on.
C: Feel how much rear push this thing puts out when Power Assist is pushing against you? That's how much brakes it has. Enough to squeak the tires. (I've seen toybuilder actually do this in a power-stop)
D: Super-brakes. More than a bicycle, skates, or your own two feet. The brakes are so powerful, they can stop you on a dime. And stay there!

By going through this, the person comes away with the feeling that "Not only does it have brakes, it has Super Brakes," and they feel like they've been let in on some extra level of secret lore. Which is true.

-iNova



http://www.glidewalk.com

toybuilder
03-23-2003, 03:41 PM
quote:Originally posted by dexter

To someone who thinks the Segway doesn't have brakes, you could say that it does have brakes, it just doesn't have brake shoes.

I guess it's a question of the audience. When I encounter someone who has mentally latched on to the notion that there are no brakes or (more to the point) a brake handle, I can't seem to get him to take my words that there's a different kind of brakes. He just won't doesn't see it, and won't accept it.

So then I go into my whole "no brakes=safer" explanation, and then at the very end, I can try to tell him again that it's just a different braking system.



quote:Originally posted by dexter

I think another reason it is safer is that the braking system handles stopping both the Segway and the rider as a single entity.


Yes. The Segway and the rider normally speeds up and slow down as a single entity -- and maintaining controlled rolling contact with the ground is critical to its proper operation. Skidding is not allowed, taking a jump and getting "air" is not allowed, and trying to "lay rubber and peel out" is not allowed. Alas, most people seem to not have an understanding of physics, so I've mostly given up explaining that unless the person is clearly interested.

And then there's the good point about the Segway essentially having an active control to decelerate its own weight when it actually does crash into something/someone... That one seems to be the most hard for newcomers to understand...

http://www.pasadenasegway.com

Do not let yourself be forced into doing anything before you are ready.
— Wilbur Wright