Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

I wouldn't worry too much, it is likely to come back round to the subject.

Ah, discussion precession!

Let me force-precess it with my stupidity : How fast can a bicycle go without any wheels ? Take the wheels off (to get rid of all that momentum) and mount the thing on a nice long toothed rail. Some good gearing and lubrication added - could I go as fast as a normal bicycle ?

"Let me force-precess it with my stupidity : "

"Stupid is, as stupid does." Forest Gump

"How fast can a bicycle go without any wheels ?"

Not very fast, in fact, it won't roll at all!

"Take the wheels off (to get rid of all that momentum) and mount the thing on a nice long toothed rail."

I will assume you are replacing the wheels with a gear or pinion to match the "toothed rail", giving us a "nice long" (and low friction) rack-and-pinion mechanism. Some mountain railways work on the same principle, using cogs and toothed rails to keep from sliding instead of smooth wheels and smooth rails which could slip on the steep slopes.

"Some good gearing and lubrication added - could I go as fast as a normal bicycle ?"

Theoretically, yes, however you will not have the stability of a normal bicycle. Sort of like trying to balance on a bike when it is NOT moving. Ever try that? Hard to do. If you had some sort of guide rail, or may be a large battery powered gyroscope mounted on your luggage rack or bolted directly to the frame, you could keep from falling over. But then with the gyroscope, you are back to having angular momentum.

Another caveat: The gearing on your pedal-drive may be lower than your rail, so you would need larger diameter pinions, but then you would be right back with the angular momentum you wanted to get rid of.

Stability: skiers and skateboarders manage alright, they just wobble from side to side a bit...........Ahh, back to angular momentum!

"Stability: skiers and skateboarders manage alright, they just wobble from side to side a bit..."

Well, you are also talking about a relatively wide base, especially for skiers, around one foot or so, usually, between skis. Skateboarders generally have four wheels, with several inches between, them, up to 4-6 inches or so by what I have seen. I was assuming that the "toothed rail" would be no wider than a railroad rail, about 2 inches.

Now if he wants to use two rails and 4 pinions/gears, it could be very stable.

Also, skiers and skateboarders use their whole bodies to try to maintain their equilibrium, while a bicyclist must use his upper body to steer and his lower body to pedal. Pedaling especially would through some wild cyclic torsion onto the bike frame, making it even harder to balance. Ever watch a cyclist at low speed? He wobbles quite a bit from side to side and must shift weight to compensate. On the other hand, high speed racers take banked turns with ease, their wheels functioning as perfect gyroscopes to keep them from falling over.

BTW, there is a new skateboard advertised on TV called a "Caster board" that uses only two wheels or casters, and at least one of them swivels. I will bet that is very difficult to balance, more like true surfing or trying to do in-line skating on one foot!

I think that you are right that it would be difficult to balance on a narrow toothed rail. But I don't see that the gyroscopic effect would help much, although it could reduce short-term wobble. I think you would have the same difficulty with a normal bicycle on a standard railway line. Having both mono-skied (one narrow ski) and cycled, I'm pretty-much convinced that the dynamic stability is achieved by steering so that the wheels (or ski) move sideways relative to the centre of gravity. This is much easier to achieve if you have significant velocity; but it would be verging on the impossible if you only have a couple of inches of available lateral steering.

I've always attributed the size of the low speed wobble I think you are describing to slow pedalling when going uphill, so that the cyclist is using a lot of force on each pedal in turn for quite a long time. Where the cycle has sufficient gears so that the force is reduced and the durations reduced, you can cycle at relatively low speeds without much wobble.

BTW, I did once (only once) use a folding bicycle with ridiculously small wheels; I didn't find it significantly harder to balance than a normal bike - but it was the very devil over bumps. It was the sort of experience where all you want to do at the time is forget about it - and in retrospect wish you'd investigated how much of the problem was the sudden rise of the wheels over the bump, and how much the lack of rigidity of the cycle itself.

Returning to my view on the inefficacy of gyroscopes to aid balance on a bicycle - maybe some fool-hardy soul would care to see how long he can balance on a cycle that is supported on a couple of pivots on the frame of a bicycle - with (or without) the wheels rotating rapidly?

Fyz

Well you would get some advantage from the rigidity of the steel and the flat profile of the rack and pinion, even over only a couple inches, versus the rounded profile and somewhat flexible material of a rubber tire over flat ground. Thus you would not need as much additional stability for the rail version.

My room-mate in college was a cycling nut, and he had an indoor training device that consisted of three rollers in a frame. You set the rear tire between the closely spaced two rear rollers, then let the front tire rest against the single remaining roller at the other end of the frame. This allowed the cyclist to pedal and train inside during very cold or rainy days. Unlike some trainers, you did not clamp the frame in position, but rode much more naturally. I believe the resistance was adjustable to simulate hills and air resistance. It was very difficult to balance while still or at low speed, as most people correct their balance by turning (I am sure you have seen slow speed riders doing lazy "S"'s), however with this device, any angling of the steering left or right would soon find you running off the 12-inch long roller. Once your speed increased it became relatively easy to hold it in a straight line. I attribute that to the added balancing of the gyroscopic effect of the wheels.

By the way, there is an excellent article on the first known "Gyrocar" at the Museum of Retro Technology website. Other gyrocars, including one 1961 prototype by Ford, are featured there as well.

This Gyrocar was an early 20th century Anglo-Russian invention that rode on only two wheels, using a large horizontally mounted flywheel gyroscope, and was marvelously stable, even allowing passengers to hop on and hop off while in motion or while stopped. It had plenty of other drawbacks, but stability was NOT one of them!

Unlike the vertical gyroscope, as in the challenge question or the wheels of a bike or motorcycle, the horizontal mounting allowed turns to be made without leaning the vehicle. In fact, any force that might cause a lean (like the body lean that normally accompanies a standard 4-wheel car while turning) would be resisted and any leaning motion would cause the gyroscopic effect to correct the axis and bring it back to vertical, just like a spinning top (vertical axis) that gets nudged.

I admit it - with GM1964's support you have made the point that gyroscopic action does eventually come into play. Not having seen the training machine, I would still wonder how much of the improvement would be gyroscopic, how much down to the increased frequency of the pedalling, and how much down to increased effect of castor and the reduced steering angle* that would be needed for a given rate of offset - possibly some of each?

*Presumably steering angle as such would be quite counter-productive when acting between rollers?

Fyz

People wobble at very low speeds on motorcycles, so I think pedaling rate is not the predominant factor. I have a 21 speed road bike with a near-mountain-bike low, and when I pedal up hill, I haven't notice less wobbling in very low gears and higher cadence vs higher gears and lower cadence -- but it could be there -- I'll have to experiment.

Ken

I appreciate that - it is a different effect to the one that I thought STL Engineer was describing.

I think the difficulty is due to the castor of the front wheel. This provides a moment that is in the opposite works in the opposite direction to that derived from the forward motion. I believe you can even balance a stationary bike - by turning the handlebars in the reverse direction to that which you would in motion.

If the above is correct, it would lead to a range of (low) speeds at which the conflict between the initial effect of the caster and the longer-term effect of the curved movement at the bottom of the wheels the bike is rather difficult to resolve.

Part of the effect at low cadences is due to the increased forces applied sequentially at each side of the bike while pedalling.

If a lower gear is chosen the force used is less, and for a shorted period, so giving rise to less sideways movement. A higher gear needs greater force, which has sideways effects as well as rotational.

See this for evidence that force on pedals gives more sideways motion regardless of speed.

Thanks - although I think you are agreeing with me. However, the comments in #133 relate to the difficulty of balancing a motorbike at low speed.

It would also be relevant to a pedal-bike if you were to ride a push-bike that slowly, though I believe this would be appreciably slower than what you we describe as pedalling hard-and-slow. Indeed, I think the tilt of the bike when pedalling slowly has to be applied deliberately (if subconsciously) so that the weight is placed (more-or-less) above the line of support.

Fyz

Riding at a steady, slow speed can be done in a straight line as long as the gear is selected which gives a reasonable cadence - easier on a mountain bike as there is usually at least one gear which gives less than one turn of the rear wheel per turn of the crank. Racers tend to have at least 1¼ turns.

I do have a friend who rides a BMX (single gear). He can keep going at a slow walking pace by moving his feet about 1" up and down - enough to keep moving without the full forces of rotating his feet.

Yes, the critical speeds do seem to be very slow on push-bikes - something under 1/2 a mph. This must depend on the configuration of the caster. It needs to be extremely slow for certain types of track racing, where they seem to play a game of beggar-your-neighbour. If you (or he) can also balance on a stationary bike, you'll be able to investigate the critical region in between...

you can even balance a stationary bike

In my misspent youth, I rode observed trials, and I found that I could do just that -- balance while stationary. I was not a particularly good trials rider, but those who were could balance all day, standing still, (or going backwards down hill) and could do all sorts of seemingly impossible stuff on one or two wheels.

If the above is correct, it would lead to a range of (low) speeds at which the conflict between the initial effect of the caster and the longer-term effect of the curved movement at the bottom of the wheels the bike is rather difficult to resolve.

How true. I recently built a fully-enclosed motor scooter along the lines of the Ecomobile. It had retractable outriggers that would keep it upright at low speeds. At very low speeds you would steer right to go right. But at about 10 mph or a little less, you would need to steer left to go right (in other words, you would need to establish a bank angle by steering left for a short while). This is the same transition one makes on a motorcycle, without thinking about it. But when sitting inside a vehicle, and especially when sitting very low (on my machine the seat is 8" above ground) it's hard not to start thinking you are in a car, and the reflexive response you have on a motorcycle seems to evaporate. Once you start having to consciously think about making the transition, it becomes difficult. Even the Ecomobile, with computer control of the outriggers, has a tendency to lurch around during the transition. (I am now in the midst of converting my machine to three wheels.)

There is a type of accident, too common in motorcycling, in which the rider steers directly into the thing he or she is trying to avoid. The Motorcycle Safety Foundation has been teaching "push right, go right" for some time now, to get people to think about countersteering. (Pushing on the right grip, of course, turns the handlebars to the left.) But still, when people panic, as when going wide in a corner and seeing an oncoming bus, many can't resist the urge to "steer" away from the bus, thus pulling the bike up out of its bank, and straightening its trajectory -- right into the front of the bus.

There are still arguments over what makes a motorcycle turn, even among road racers. There are those who think it's all body english -- which can be easily disproved by riding a lap around a track in a full tuck, chin against the tank all the time. Without any body motion at all you can turn in an OK lap time (e.g., much better than the beginning racer). (By hanging a leg or more of your weight off the side of the bike, you can move the bike/rider CG in toward the center of the turn, thus increasing the effective [virtual] bank angle while parts of the bike are dragging on the pavement, preventing the chassis from [actually] banking further.)

Keith Code of the California Superbike School built a bike with two sets of handlebars to demonstrate how little body american (whoops, english) has to do with it.

ken - as ever in depth explanations. Could you explain the term "body english/american" please? I've never come across this.

Thanks

Many riders believe that they cause their bikes to bank into a turn by leaning their bodies, i.e by using "body english". As I first wrote that, the term struck me as funny -- particularly since so many in CR4 are from the UK. If we say body english, then you would say body american, right?

We use "english" to mean twisting or spinning or leaning. For example, we often put "english" on tennis balls by tilting the racket a little, which causes the ball to spin.

I just looked the term up. We use the term "english" in billiards, too. I notice that in the UK, the equivalent term is "side." I think, but am not sure, that when we use the term "english" in sports we don't capitalize it.

Just confirmed the latter: http://www.word-detective.com/070698.html

I'd never researched where the term body english came from until just now, but the link above explains that too. Oddly enough, when we talk about body english in the more literal sense (as explained in the link above) we never say "body english". We say "body language".

(I wonder if the derivation given by the word detective, as it applies to billiards or tennis, is really correct. In both cases, the difference beween a straight shot and an "englished" one is very very subtle. In billiards it amounts to simply hitting the cue ball off center -- no "body english" required.)

There we are, back on track after my diversion, talking about spinning objects again. Does the fact that the discussion naturally returns to topic disprove chaos theory?

"body english"

I'm so glad you explained that Ken , I was really getting baffled ! I am still churning over all this steering chat. (I'd always thought it came down to getting the the tyres tilted by shifting c.o.g. - I will have to read everyones interesting posts on the topic )

You can certainly steer a pushbike by shifting C of G. It's all to do with the caster on the steered wheel. When you lean, the weight of the bike is applied ahead of the ground-contact point of the wheel, and causes it to turn so it points in the direction that the bike is leaning. The order of events is:
You lean right, the bike leans left, and the wheel initially points to the left
The bottom of the bike moves around to the left, your weight is now to the inside of the turn you wish to make, and the bike leans to the right, so the front wheel now starts to point to the right.

If you tried to implement the whole of the process consciously while cycling, I expect you would fall off.

BTW, when I first heard the term "English", it was explained to me that this was because the English never went in the direction that Americans expected. Even though I had previously explained I had no right to be called English, I doubt it was intended as a compliment.

Fyz

Thanks for the explanation. All the factors involved in steering ,clearly add up to a complex whole that few people grasp. As has been pointed out -that could be a fatal lack of understanding.

I'd never heard the use of 'english' this way before. In a way , such a phrase is more 'English' than the 'English' would dream up - if that makes any sense ! Whatever the origin , its put a dashed good smile on my face , what.

Where is that rhetorically absurd 'what' from.

When controlling the bike by leaning, I have found it best not to grasp the handlebars

Very cunning . I go off at so many tangents that I recognize oblique when I see it ! Even my trick-cyclist knows this .

You lean right, the bike leans left, and the wheel initially points to the left

Good analysis. Most people are unaware of this, and most do not appreciate that to lean right on a bike, you must have something to react against, namely the bicycle itself, which must initially move leftward.

It's something like government: for every lean to the left, there is an equal and opposite lean to the right.

"Pushbike" is another one of those terms that makes more sense on one side of the pond than the other. At first, I thought you were referring to small stand-up scooters, which are pushed along with one foot or the other.

I have just twigged what you mean about weight-shift/reaction/lean Ken. I'm definitely getting senile. The skill to do it the right way must be considerable - much more finely controlled than steering a car into a slid (yeah , I know the analogy is loose )

For your general interest.

'UK Police have found fatal problems with Honda Pan European ST1300 bikes. Modifications for police service caused high-speed (shock) wave at 110 mph , due to an increased cog. An officer was killed recently' (The Times )

I heard that a Chief Constable over here injured himself very badly (lots of broken bones) when demonstrating to his bike officers that there was nothing wrong with the bikes. They scraped him up off the runway on which he had been showing them that the problem was with them and not the bikes. Following the accident, all Pan-Ams were withdrawn from operational service.

Great Link!!

I've done some aerobatic flying, and some windsurfing, a little hang gliding, some motorcycle racing, etc. and have been fairly competent in several of those. But in every one, I run into people who seem to be a full order of magnitude better and much less fearful. My jaw drops, and I just wonder how that can be possible. I've never tried unicycling, but it certainly looks like it would be difficult on a level surface -- but on a mountain!!???

Sad to hear about the ST 1300 and its riders. I've spent many fond moments on Hondas, some of which were as near to perfect in handling as can be imagined. But almost any bike can be provoked into "tank slappers" given unfavorable weight distribution, the wrong tire profile, loose steering head bearings, loose swing arm pivots, etc. The Honda 550 Four, when it first came out, would wobble at certain speeds (even with a brand new properly set up bike). Our team raced one for a couple years and it was a superb bike after we did a little stiffening of the frame around the steering head area. In its stock configuration, it was not so fast that it got too many people in trouble, but it certainly had the potential for tossing off its rider, and Honda could have done what we did for an extra $3.00 per frame, I'd guess.

But in their defense, I'd have to say that wobbles can be pretty mysterious. I raced a purpose-built racer for a couple seasons. (It was built as a class project in a technical school where I taught.) Its handling was faultless -- the sort of bike on which you could pass people both inside and outside the "proper" line through a corner with impunity. But I had quite a scare when I sat up to pull into the pits and raised my left hand to signal. The bike went into immediate tank slappers (full lock oscillations), which, fortunately, I was able to stop before getting tossed. The whole thing only lasted a second or two, but they were memorable seconds. The bike was only 200 pounds, so its reactions were very fast, and consequently the wobble developed with light switch quickness. But that same lightness made it easy to stop the wobble just by holding the bars firmly. Not so easy on a bike with the mass of an ST1300. Nevertheless, Honda probably could have done a better job in helping to ensure that these bikes were better set up -- in police usage they are almost certain to be too heavy in the rear, which promotes wobbles.

My take on the ST 1300 story is that the dangers of modifications were known for quite some time by the Police. I'm sure that they have some top riders testing bikes before they get selected for service , and the modded bike would also have been put through the mincer. It may be that bureaucratic inertia stopped feedback from getting the serious and real danger noticed until too late. The Officer I read about was under training on a Motorway . I'll see if I can find more specific detail sometime.

Glad you liked the link. I have to agree , it's pretty astonishing what some people can do on wheels.

It's the latest model that's causing the problems, so I've heard. An my mistake, it was a Chief Super, not the CC as I said above.

One of my Sisters is a Police Inspector in the Midlands. Next time we talk I'll ask her for the inside version of things.

ps - A new Q is out. It's perfect for your saga - a full moon ! I think somebody is playing the whole CQ thing just for you.

Hi Ken,

Your story about the 550 brought back a few memories of a CB 650 I once owned. The bike would start wobbling at around 140 km/h (quite scary!) and I remember that the only way I could re-gain control was to push forward as hard and evenly possible on the handle bars. I always thought the problem was inherent to my bike only. Otherwise, I loved that bike since I used it mostly in the city (light and very manoeuvrable). I learnt to be more "careful" when I hit the highway.

Ken,

The double-barred bike article was excellent !! My Dad tought me this some 30 years ago even though he didn't understand the "why it works". He was an excellent rider which made me a (at least) decent one. I had a lot of discussions with riders about this subject, some of which got really animated. I will keep the article since I'm convinced that these discussions will arise again in the near future...

Have you ever been riding with a passenger that was scared to "lean" into a curve (scared to follow the movement of the bike)? Now THAT's dangerous!!!

thanks,

Rick.

Have you ever been riding with a passenger that was scared to "lean" into a curve (scared to follow the movement of the bike)? Now THAT's dangerous!!!

Funny, just reading that gave me this very visceral adrenalin rush. I've never had a passenger actually cause an accident in this way, but I've had several heart -stopping experiences.

I can imagine the heated conversation after the crash (assuming survivors are available). "What the hell did you do that for!!???" "Because it felt like we were going to crash!!!! And I was right!!!"

That sounds just like playing Bridge opposite my sister-in-law.

I've had to let off my passenger once because she wouldn't follow the movement (almost making me crash into oncoming traffic). I was mad but proceeded to explain to her as best I could why she HAD to do it. When she repeated the "non-conformance", I had to let her off. I called a buddy to pick her up (in a car) and went on my way. I realise thatit wasn't very gentleman-like but killing both of us in a head-on crash would not have been either....I chose life, I guess...

Reminds me of the only time I rode a ski-do. My (then) other half was on the back and wouldn't shift his weight about (I believe he''d ridden motorbikes when younger) even when I asked him to. Bizarrely, he commented on how my shifting my weight when on the back helped him drive! Then again, he always was a selfish b******. LOL

Thank ken. That article made me think again.

On my bike training, I was told about counter-steering - or rather reminded to use it, as I already understood that it worked. When out riding yesterday, I was musing on this thread and paying attention to what I was doing - or what I thought I was doing. To me, it now feels like I turn my bike like I turn a kayak - using my backside to provide the point of contact. This automatically makes me/is a consequence of me counter-steering (no idea which comes first). In a kayak I would execute a rapid turn by using a bow rudder on the inside and would edge (not lean) to the inside. Thus I push my inside hand forward - not that I notice! My upper body doesn't move - until I take a really tight corner and I feel my self moving instinctively towards the classic bikers' pose (although I make no claims about being any good!).

So I think that although my reasoning is squiffy, it appears that I'm actually doing (mostly) the right thing!

Good motorcycle/kayak analogy. I agree they can feel quite similar.

Yes at low speeds on a motorbike you can wobble - but many riders don't and their secret is to use the gyroscopic effects from the engine to stabilise them (we were taught this trick at training, and I was the only one who could see why it would work).

Most motorbikes have wet clutches, which allow them to be slipped without damage. At low speeds, a motorbike rider aims to keep engine revs (relatively) high - constant throttle, and to slip the clutch to contol road speed. It really does work - at least on my little single. I'm not sure if the effect is lessened, not ridden one of those.

That is interesting, thanks. Do all motorbike engines have significant flywheels, or can multi-cylinder bikes manage without - in which case I wonder how fast the engine needs to rev?

Fyz

Mine's a 125cc single & for low speed stuff, I estimate that I hold the revs at about those needed for 20-30 mph in normal riding in gears 3 and 4. There's no rev counter on my bike, but as a noise engineer (lapsed) my ears are fairly well tuned!

Doing this takes a bit of getting used to - well it did for me as I change gear totally on engine note, and drive a diesel car. The "screaming" petrol was quite distressing at first, and I still change up a fraction too early.

Multis tend to have no more flywheel mass than required for structural rigidity and dynamic balancing of the crankshaft itself, and that mass required for the alternator, which is usually on the end of the crankshaft. (These often use a rotor which is between a stationary inner field coil and an, also stationary, outer set of charging coils. Sounds like magic, but the rotor is oddly shaped and has north and south poles induced into it by the field coil.)

In the original Honda Gold Wing (a flat four with longitudinal crank) the alternator was gear driven in reverse to cancel some of the gyro effect of the engine. BMWs of the day had real flywheels, like a car engine, and when you revved the engine, the bike would react by listing to the right. Honda, in their typically thorough way, thought that you wouldn't want such effects causing the bike to bank more or less as you went through corners and changed engine speed.

Hey STL, your gyrocar links are so, like, totally five minutes ago, dude. If you look at my post #56, you'll see that the link goes to the same gyrocar page. That shows that there really are commonalities among deranged minds.

I think your explanation of the Schilovski gyrocar might be a little off-kilter, catty-wampus, or half-a-bubble out of level. It banks into turns, and the front view drawing shows the maximum lean angle. The pendulum arrangement causes the gyro to tilt fore and aft to generate a tilting or restoring torque, according to the vehicle's turn rate. Thus the passengers would not be subjected to lateral G forces associated with centripetal acceleration: It would feel like a motorcycle or airplane.

When the vehicle was stationary (or moving in a straight line), having someone step aboard the left side would cause a tiny tilt, and the pendulum would swing slightly to the left. This would tilt the gyro fore or aft (depending upon its rotation direction) to generate a restoring torque to the right. In motion, when entering a right turn, the pendulum would again swing to the left, causing the gyro to again tilt in such a way as to generate a torque to the right, in this case tilting the vehicle to match the G force, airplane style.

The much later Swinney (1962) was called "the first gyro-stabilized car ever built that does not lean when subjected to unbalancing forces. It remains fixed in the exact vertical position." Why would anyone want such an arrangement? Banking into a turn is more comfortable than being thrown into a door while cornering. In more recent tilt vehicles (GM Lean Machine, the Carver) leaning is considered a virtue, not a vice.

Based on Swinney's patent and concurrent monorail work, I suspect that "vertical" would have referred to the apparent vertical (including centripetal effects). The only purpose that I can see for a gyro on a non-monorail system would be to make attitude control easier at low speeds.

I don't know of a gyrocar whose wheels were not in-line - it would seem to be easier to apply correcting forces via the suspension. However, non-banking is at least an improvement (for passenger and driver) on the typical outward lean generated by passive suspensions. I also suspect that if the stabilisation system is applied as a supplement to an existing suspension+tyre arrangement, non-banking could be optimal for handling, as it keeps the tyre flat on the road. (Motorbikes are a different matter, as they don't use a flattened region on the base of the tyre, and the tread pattern is varied according to lean, so you can choose optimum between maximising forward traction or economy when upright and still generate optimum lateral traction at sideways lean).

Fyz=Deranged^3

There's more than one way to reduce banking in cars - hydractive is one - and it softens the ride.

Indeed - this is one example of doing it via the suspension. Presumably the "active" bit is needed to avoid the side-effects that BL's hydroelastic suspension provided in the old 1100 (though it seemed to work OK in its original incarnation in the mini)

The two systems are quite different: BL's connected front to rear, and required a special pump to be used - hence a visit to the dealer, while Citroen's has a pump built onto (or in the case of the GS, INTO) the engine, to give pressure as required, while the engine is running.

The Citroen deals with blow-outs remarkably quickly, so the car continues in a straight line (or round the bend safely, if the blow-out occurs on a corner), and the car can be driven on three wheels, with the suspension in "high"! I've never seen a mini do that.

This is tempting fate (maybe it should have been in the previous challenge on statistics).... I've driven several cars that have had blow-outs, and none of them lost steering control.
And that ability to run without a rear wheel must be really useful when it's a front wheel that has a problem.

The problem with blow-outs is not nearly so bad with steel radials - I had a n/s/f tyre go on a VW Beetle which was not belted: bent the front axle in a ditch.

Had both n/s wheels taken out in a GS - cornering on a quiet country road - into a rockfall - car stopped fine, put spare on n/s/f...........and drove home.

These days, most cars have steering geometry arranged so that the road wheel pivots around a line that intersects the road at a point very close to the centerline of the tread. So differences in drag for flat tires, low tire pressure, differences in braking effectiveness, etc. cause minimal effects at the steering wheel. The only scenario in which you are likely to loose control is when the blowout is on the outside of the car during aggressive cornering. Then, there may not be sufficient traction on the remaining wheel to keep the car going around the turn.

When I was a kid, blowouts were pretty routine in bias ply tires. I don't think I've had a real blowout (the kind that actually goes "pop!") in 40 years.

Great link! A glutton for punishment, I owned 2 Cits at the same time: a DS21 and an SM. They were great fun, and very rare here in the US, even when they were sold new here (30+ years ago).

Actually, I use a bicycle regularly and I have noticed that the main reason for extreme wobble at low speed is starting off in too high a gear - I even converted to an internal hub gear so I can change to a low gear while stationary (very useful in the city centre).

It is normal recommended practice for racing cyclists to start in two gears below their cruising gear - this is so they do not waste energy by using too high a cadence - they have the advantage of having roads closed for them and thus do not need to stop regularly for traffic lights/cars....

Gyroscopic effect is not noticable until over ~15mph - and can be a life-saver when an overtaking car pulls in on a corner, hitting the front wheel. Just as well I was travelling at 25mph at the time!

Is that relatively long-distance cycling? And do these racing bikes have any gears that are lower than the "recommended" starting gear? My (probably uninformed) thought is that some of the advantage may be gained because the train can be better aligned (for lower gear-train loss) if there are fewer gears to cover. If the races are close, I suppose it is even possible that the few ounces weight saving through minimising the gears could make the difference between winners and also-rans?

Fyz

Races are usually 20+ miles, the bikes have lower gears for travelling uphill. Weight is kept down by using just 2 front rings, but retaining 9 on the rear. The gear ratios are usually closer than mountain bikes, as keeping cadence within the cyclists preferred zone is important for endurance.

Gear-train loss is very little under most circumstances. A well lubricated and new chain will cope admirably with slight lateral offset, but as with all derailleur systems not all ratios are used. (large front ring only used with 5 smaller gears) What appears to be an 18speed system is only recommended for 10 combinations to avoid over twisting the chain.

On a mountain bike with 3 rings, "21speed" gives 12 to 15 combinations, some of which may overlap. That is why I have gone for an internal hub gearset - I have 8 speeds, in order, with only one twistgrip and a clutch, allowing change of gear when stationary. The chain is also kept in direct alignment at all times, and gear changes can be made easily and cleanly at all cadences.

Unless you have a local authority that makes roads like mine , you may have to take your own road for this bike.

If only I could really go "straight there"!

I recall that back in the 70's an Engineering Magazine ran a competition to design a bike with infinitely variable gears. By that , I mean being able to smoothly transit through from highest to lowest possible ratio. The result was a planetary type system - about 8 cogs were free to move radially (but synchronously) out from where conventional rear gears would be. My memory of this is sketchy. The gear change wire must have pulled the planetary gears outward (each of the 6 gears being retained by a slotted circular plate ). Chain tension would have moved them inward when the gear lever allowed. Each planetary cog must also have been ratcheted to enable separation as they engaged the chain.

Does this sound familiar - I'd like to see the picture of that again , now that I'm a bit older !

Ahhh! I see. Very logical. (Mr.Spock)

Here's a late thought: Going back to the beginning, nobody said the spinning wheel was anchored inside the suitcase. If not, then no outside effect should be felt when the suitcase is turned. The wheel might rotate inside the case, but don't ask me in what direction.

You are only partially correct. If not anchored, but mounted, say, on gimbals (friction-free, multi-axis bearings), so as not to affect the briefcase in any way, even by friction, then you are correct that no outside effect should be felt in this case (no pun intended). However, the wheel does not rotate inside the case. Rather the case rotates around the wheel. It is like saying the Sun travels from East to West, but in reality, the Sun is fixed relative to the Earth, which rotates West to East, causing the Sun to appear to travel East to West to an observer on the Earth.

Let's say you had a case made out of transparent material, glass, clear plastic, etc. With the gimbal-mounted wheel spinning and the person carrying the case executing a turn (left or right, no matter), you will observe that the wheel remains in the same orientation, even though the case revolved around it!

You got your rose back !!!! Nice.

Rick

Busy man?

I believe he is retired now. Lords are appointed for life. He spent most of his career in the Legal system, as both a QA and a QC. He is an expert on criminal law, and is still consulted when there is an issue in this area.

Perhaps, if the Millenium Wheel does fall down, and there are charges of criminal negligence brought.....

Conjures images of two guys on one side, and a few loaded pods on the other. Think trebuchet. "OK guys, get some tension on that rope. When you're ready, just shout, and we'll release the emergency brake."

The headlines: "Two London men fly to Paris."

Having worked in the construction industry for many years, EVERY company I worked for that dealt with concrete "flat work" (pouring floors etc) used at one time or another a portable gasoline powered concrete cutting tool for cutting expansion joints in the slab.

In all cases the first time a new employee is told to use this machine it is with direct supervision from a foreman or boss.

Normally, these tools are equipped with a 14" disk weighing approximately 2 lbs. When first started, they have a tendency to want to quite literally jump out of the operators hands. Once up to speed (8,000 - 10,000 rpm), the new operator is told to try turning around. Almost impossible!

At a few of the places I've worked, only a select few were allowed to operate this highly dangerous machine. Very easy to hurt yourself or others with it if you aren't aware of the gyroscopic effects.

It is possible he never made it to the door.

I cannot think of anyone walking into a room around a suitcase and then picking it up, the normal movemnt would be to pick up the suitcase and turn around to go to the door. Whch ever way he turned it would resist his movement in that direction and try to trip him up.

Well its food for thought !

He passed through the other entrance to the suite, and thus tripped over the remains of the meal from all of that thought.

An intro:

I'm the nut that posted #74

While I am not a school trained engineer, I do love to tinker around with various disciplines of physical science.

Mostly though, I enjoy expanding my understanding of the world around me. Thusly, I like reading the discussions on this board....been lurking for quite some time...just thought it time to actually register...

Welcome - the coffee pot's in the corner...there's usually food of some sort here (today's special is tripe)...no smoking though, please!

Just hold this brief case for me a moment, now over to left is the best sofa....what are you doing to that briefcase?!

That would be funny to see. Maybe someone will build that and videotape for all to see.

1. Friend turns corner, feels wrist tension, looks at dislocating wrist, walks into door frame and suffers concussion, then falls over case breaking leg.

2. Physicist wife scorns husband, sides with friend then helps with his recovery.

3. Former friend files lawsuit.

4. Suit is settled out of court for undisclosed amount.

5. Former friend and former wife jet off into the sunset.

The way the case moved did not affect the settlement!!!

Next Question.... How long before the couple run out of money?

Doug E. Fresh

Exhibit A: gyro-suitcase.

Judge: "Who in the world would build something like that?"

.........................

Wow! I think you should post that as the next challenge question!

Mark

I wonder if anyone has tride this with a laptop/notebook PC. Doesn't the hard drive spin continously? I know the speed is very great, but the mass and moment of inertia may not be very large.

Is it possibly to feel the gyroscopic effect if you try to rotate the PC other than around the axis of rotation of its hard drive?

Possible - but the masking effects could be significant - relatively rigid (mains and monitor) cables, and there is a lot of other mass. It might be more apparent on an external USB drive - less mass, and less cabling, and still 7200 rpm.

I wouldn't be inclined to try too hard unless the disc was expendable, though.

As i see it, the wheel is turning relative to the case. when the case is picked up ,the

entire case is moving relative to its enviroment. When the case is sitting on the floor

(before it is picked up) it is not trying to do anything, so why would it when it is being held. If you carry a running fan, it does not try to lead you in any direction,

so why would this case. i dont think it will do anything.

Although seriously intrigued by all of these answers, I feel that the most important aspect of "What happened to the case when his friend exited the room and made a left-hand turn", comes AFTER all of these comments …. The friend picks himself and the "possessed" briefcase off the floor, realizes the prank that his friend the physicist just played on him, and hurls the briefcase at the physicist laughing his butt off on the other side of the room. I sure hope physicists can duck, because that will determine the "final resting place" of said briefcase. End of story.

Ok guys - late I know, but I've been too busy to type it in one go - I wrote most of it on Tuesday night in the doc's waiting room (it was warm and no-one disturbed me...saves on the bills at home!). Episode 4 is now on the Blog.

Edit

Ok - it will be there at 1400 BST (I hope). Because I was typing it in stages, I put a delayed start on it, and it seems I can edit this start time, but not remove it which is what I tried to do. Let the anticipation build!

I've just been to check and the time of release has been changed to 12 May 0200 - but I have no idea which time zone this will be!

Here's hoping it will be released before Monday!

<mutters>Next time I'll type in word and copy it into the CR4 editor...much safer!

Headline from "The Sun"

GOTCHER

Put otherwise: "Do you really think you can elude Murphy that easily?"

That's it . You lot are making my brain cell ache. It is 17:12 ER

The force analogy is OK, but from the description of the situation you may have the direction of rotation of the suitcase wrong. The basic concept here is that the rotating wheel will resist any change in angular momentum, trying to maintain the same angular momentum. You can find the direction of the angular momentum vector by curling the fingers on your right hand in the direction of rotation. Your thumb sticking straight out will point the direction of the angular momentum vector. I assumed that this vector pointed away from the person as they picked it up with their left hand. (If you meant the other way, then your direction of rotation is correct.) As the person rounds the corner, turning to their left, they are imparting an angular momentum to the suitcase and the spinning wheel inside. As they turn left, the newly induced angular momentum vector will point straight up. This means that in order to cancel this change in angular momentum (keep it the same as it was before the turn) the angular momentum vector for the spinning wheel must point downward. In order for this to happen, in the scenario I assumed with the original spinning wheel momentum vector pointing away from the person carrying the case, it must turn outward and the top and inward at the bottom, smacking him in the knees with the bottom edge of the suitcase.

physicscross

Forget the clockwise bit - that's ambiguous. But the question also says that the top of the wheel is spinning towards the front of the case - and that is perfectly clear. The top and bottom of the wheel want to keep going in the same direction as before; straight on for the top is towards the friend, straight on for the bottom is away from her.

Reader

What a far out explanation . Look at #181

Couldn't find 181

It's on the first page, after ##14 and 180

Cheers , I was going nuts !

I cannot believe these people are engineers. Kind of makes you worry.

Makes you understand the prevalence of large departments devoted to checking that designs actually work, perhaps?