On 2011-01-31 16:48, RussellMc wrote: >> Yes, that thing is an accident waiting to happen... There is no physical >> basis for emergency stops! > No. There is a basis that appears to allow about as high a degree of > braking as you could reasonably hope for. Read on - I have a few hours on Segways and my dad held a franchise at one=20 point.... I am fascinated by their control software. There is no question of coming up with the torque to stop from speed -=20 the machine will try very very hard never to allow you to attain such a=20 speed in the first place. The control system KNOWS your momentum and=20 KNOWS how much torque the motors can apply and KNOWS how much battery=20 energy is available. It simply will not let you reach a speed it=20 cannot bring to a stop or balance. If you try it will shake, beep, and=20 slow you down. The appropriate motion for an e-stop is in fact "buttocks out and down"=20 like you're trying to sit. That will rapidly and stably move your CG=20 back and downward (and cause you to reduce your steering input). The=20 balance loop will apply reverse torque (and fast) to keep your CG over=20 the platform. There is no separate control action necessary - there is=20 already lots of torque margin available to keep the machine upright. Going down a hill it will back you WAAAYYY off because it knows how much=20 deceleration it can muster and limits your speed. In fact it goes down=20 hills more slowly when the battery is full, because it can't dump=20 dynamic braking energy into the battery. This is quite disconcerting to new riders who try to coast the machine=20 down a hill, while it pushes the handlebars into their chest/gut trying=20 to get them to lean back.... quite unnatural on a downward hill. The=20 "sit down" motion is effective here because it doesn't feel so weird. Also, with a top speed of 12 MPH, it's not out of the question to just=20 step off the rear of the platform; it will sense your dismount and come=20 to an upright stop by itself, and then idle and fall over. I have=20 stepped off the machine at full speed in sticky situations, and have=20 managed not to go down face-first! Getting the wheel stuck against a curb, in a grate, or against a door=20 frame puts you in much more immediate peril, because the control system=20 can't predict these events and can't apply reaction force to keep you=20 upright due to the stopped wheel, and it will buck quite wildly trying=20 to maintain balance. It is good to learn to step off right away in=20 these cases, rather than try to control the machine out of an=20 uncontrollable situation. Another "gotcha" is turning at speed without crouching into the turn. =20 The machine will happily make a sharp corner while your body mass=20 continues forward, throwing you over the fender. I have never really had a problem on sand, dirt, leaves, or gravel. =20 Taking the "offroad" Segway X2 up a mountain trail is quite spectacular;=20 it has fat, low-pressure, knobby ATV tires on it, and it doesn't mind=20 climbing a steep hill at full speed. And you get your battery energy=20 back on the way down! Joe T > My total Segway hands on experience is under 30 seconds, but ... > > You could have an emergency stop mode where you leaned back and it > held you at a suitably steep rearward angle and then decelerated using > body weight as reaction torque against the brakes. Assume ~~~1 metre > circumference or 60 RPM of wheels per m/s forward velocity. > At 5 mph you get about 300 RPM. > > Power ~=3D kgm torque x RPM Watt > For a say 80 kg rider and 1 meter moment arm and 'less than fully > laid' back rider you get say 50 kgm torque. > That's an available decelerating power of 50 x 300 =3D 15 kW of braking. > More than you are liable to be able to generate even by a full short. > That power increases linearly with speed and is proportional to moment > of body mass x rider c of g behind axle distance. Even as you lean > further back you maintain wheel downforce as approximately constant > as long as therider doesn't touch the ground. > > Getting very BOTE without an E and E&OE (should be elsewhere) I > calculate around 1 g potential braking for rider + vehicle in that > situation at 15 kW available braking energy. May be well out but odds > are that you would have all the braking force that traction would > allow you in most cases. . > > Body c of g for a standing person is typically about at the groin. > Crouch down and it's less, so the 1 metre assumption above is probably > high, and the lean angle needed would be severe - but it depends on > how seriously you want to stop. > > My point is that the Segway does have a mechanism for rapid braking if > anyone cared enough to develop th e program required to handle severe > rearwards angles of lean and if riders could tolerate it without doing > something that upset things. Even a mode that did this as well as > possible and then failed into a "lay you on the ground on your back" > mode would be more tolerable in many cases than other alternatives. > Probably as acceptable as the step/roll/slide/flop off a motorcycle > alternatives under excess emergency or enthusiasm situations. (I > managed many 100's of those without significant injury - I suspect a > Segway could learn to be > > Full laid down with the "'rider" at the rear and still providing > reaction torque you get maximum available torque but reduced wheel > down force (no rider weight). In this mode wheel downforce is provided > only by the machine weight so youd probably go into a skidding mode > with the rider lying down head rearwards and feet on footplate. > > > Russell --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .