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The most spectacular accidents can and will happen when you touch the rear wheel of the guy before you with your front wheel while trying to stay close behind.
My link roll is mounted between two horizontal rods extending from the rear wheel hub. With a diameter of a few inches, it has a surface of
polished or chrome steel or any other material with very low friction.
Now when you are catching up with the fast cyclist before you, don't worry about too close contact with his/her bike. Just keep spinning and enjoy the ride. And don't forget to mount the device to your own bike as well to become a pacemaker for the lesser endowed citizenry.
Cf. motor-paced racing where a similar device is mounted to the pace making motorbike. Make it lightweight and compulsory.
Sketch
http://CoSketch.com/Saved/pV1SHCh2
A poor sketch of this. [scad mientist, Dec 03 2014]
[link]
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Having been spectacularly accidented by a guy who thought he was being cute cutting in front of me I can see some potential applications for this. |
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WTAGIPBAN. On a bike idea no less. |
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How is this different from the chromium-plated mudguards which every bicycle is already fitted with? |
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I think, translated into British English, that's "Mount a roller behind the rear wheel.."? |
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//How is this different from the chromium-plated
mudguards which every bicycle is already fitted with?// |
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Because it spins when the other bike's wheel makes contact
with it. I'm not clear from the post whether it is supposed
to ride against your rear wheel (so that it is already at
speed, but would be an annoyance the rest of the time) or
is simply free-wheeling, but either way, there would be no
tendency for the rear bicycle to try to climb the front,
resulting in a much safer bike-bike interaction. |
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// WTAGIPBAN. On a bike ... //
*WTAGIPBAN yourself*, you bloody ... oh, it's a compliment. Thank you. |
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// I think, translated into British English, that's "Mount a roller behind the rear wheel.."? //
Yes of course. Further translation help welcome, english not being my first language. |
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// ...whether it is supposed to ride against your rear wheel... //
No it's not. This would not eliminate the potential danger in touching the spinning roller which would be driven by the rear wheel of the bike in front. |
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I just discovered Cosketch which seems like a nice
platform to use for sketching ideas for the
Halfbakery so I decided to try it out. See link.
[Toto] feel free to delete the link if you don't like it
or if you create a better one. |
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Of course according to their terms of service,
there's no guarantee on how long the sketch will
remain visible... |
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On viewing [scad mientist's] sketch it becomes clear that the rigidity of the apparatus and the lack thereof might pose a problem. What may definitively not happen is that the roller touches the rear wheel. Therefore either the horizontal rod has to be quite rigid and heavy, or it has to be integrated in a triangular framework - maybe into a pannier? Or extend the frame tubes going to the rear hub so that they connect at the mounting axis for the roller. |
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//...for the lesser endowed citizenry// - how do you know this? - they might not be wearing lycra |
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// they might not be wearing lycra //
The muscular endowment shows in their speed. That of the corpus cavernosum - well, that's another story. |
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Hi [Toto]. Are you new here or just an [Alterother]?
Welcome anyway. |
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I don't think the roller contacting the rear wheel would
actually be that much of a problem. The reason
wheel/wheel contact is so bad is because the wheels are
moving in opposite directions at the point of contact.
The rear bike tries to climb the wheel and the front bike
tries to tip backwards. If the roller is in between, the
points of contact will be in the same direction. |
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And since the surface speeds of the bikes are very similar
(this won't help in a high speed differential contact), the
points of contact with the roller should be at similar
speeds. |
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If you had a set of rollers attached to your rear wheel, such that the roller 'exposed' to the rear was geared down slightly and going slightly slower than might be expected but in the 'right' direction, then any touch by a bike following too closely would have the effect of sapping power from that bike and increasing your speed slightly and decreasing their speed. |
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// roller 'exposed' to the rear was geared down slightly and
going slightly slower than might be expected but in the
'right' direction// |
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To do this you just need a slightly smaller rear wheel than
their front wheel. Just another reason my 26 x 1 3/8"
wheels win in a world dominated by 700c. Now, i just have
to figure out how to make it do more than 10mph. |
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No, you'd need a slightly larger rear wheel than their front wheel to ensure that the roller was rotating slower than expected and would then be sped up by a touch of their front wheel. I think that's right, anyway. It's quite a hard thing to imagine. |
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The wheels don't matter. If the bikes are at the same
speed, the outer (contact) surface of the wheels are at the
same speed. You would need a pulley or wheel and axle to
get the required mechanical advantage, which means at
least 3 rollers involved in order to get the mechanical
advantage and the rotation both correct. |
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Yup, had to work entirely through the maths to convince
myself... a 2068 mm circumference tire moving at 10 mph is
revolving at 2.16 revolutions per second and a 2200mm
circumference tire is revolving (proportionally) more slowly
at 2.03. You multiply them up and you get the same ground
speed in metres per second (4.47). |
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I think some kind of viscous coupling is the way to go, to
steal torque in a less jerky way. |
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The discussion somehow steers in a wrong direction. The main advantage would be aerodynamic coupling of two bikes. No need for further help or stealing advantage from or for the front or rear driver. |
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Just came back from a 100 km (de)tour without any pace-making help in sight but with lots of time to ponder. |
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How about moving the apparatus to the front wheel -? It is mainly in the interest of the rear rider to get close to their pace-maker, so they should bring the equipment, too. Could be an integral part of a low-rider front pannier, or just a standalone contraption, bolted to the hub axis. It could even serve to hold a mudgard reaching a quarter circle more to the front than the standard. |
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Yeah, discussions here do that, you get used to it. |
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The front wheel thing makes some sense from a
responsibility stand point, but it's going to be harder to
mount. With the rear wheel, you can clamp to the chain-
stays, which tend to be geometrically consistent, and
most bikes have them. so the mount is a simple tube. |
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On the front, you don't have that line, so you're going to
need a more elaborate frame that bolts to the
pannier/mud guard mounts. However, since a lot of
racing bikes (the type most often ridden in pace lines)
don't have these mounts, your'e also going to need a
version that clamps to the fork, in multiple spots, and
then you're going to need adjustment to correct for
different rakes and tube shapes. |
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//and the front bike tries to tip backwards// bollocks. |
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I didn't mean to say it actually does tip backwards, just that
that's the direction of force
involved. It's going to tend to present as a rear wheel skid,
possibly with a sideways element depending on the exact
contact. |
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Any number of ways to make the initial 'two wheels hitting each other' less bumpy, storing the energy in a spring or bungee cord. |
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Imagines possibly 30 bicycles, nose to tail, cycling around in a ring. Given the aerodynamic advantages, it might be possible to achieve something near the speed of sound. |
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//it might be possible to achieve something near
the speed of sound.// |
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Or not. Rolling resistance scales approximately
linearly with
speed (constant with distance traveled), and is
equal to air resistance for most
riders somewhere around 12mph. Wind resistance
goes up as the square of speed. Therefore double
the speed equals 4x the force for wind resistance.
So that 24mph cyclist can maybe make 60mph. |
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The record individual time trial (no drafting) for a
cyclist is 34mph, which means ~8x the power
input. |
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108mph theoretical max. This is probably a
realistic, since the
peak for a human powered vehicle (fully faired
recumbent) is 86mph right now, and those are
highly streamlined. |
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Ah. While trying to work out if it would be possible with sulphur hexafloride (it's not) I just decided to give up. |
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But then I remembered the bicycle Ouroboros would function best in a large vacuum chamber anyway, so cutting down air resistance and pushing the local speed of sound down to about zero. |
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// ... the bicycle Ouroboros ... // I couldn't help thinking of the scene in "Day of the Oprichnik" where a group of russian pretorians form a circle by each penetrating his colleague while being penetrated by another one. I swear this isn't what I had in mind when devising my bike train. |
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Truly one learns something new every day.... |
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//108mph theoretical max.// |
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Are you allowed a high altitude plain and 100% oxygen to
breath? |
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That was based on zero wind resistance, so you won't do
much better than that with regard to altitude. |
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The base speed I used was based on the current time trial
record for short (3 mile) time trial records. I realized I
missed a category there, and the record for the flying
(rolling start) 200 meter sprint time trial is about 47
mph. (I'm using time trials because they are
unpaced/solo, so no drafting to improve wind resistance.
That allows a baseline using my 12mph number above.)
That's
probably about as close to an instantaneous peak as you
can get (it's less than 10 seconds). |
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That might push the limit up towards 200 mph with no
wind resistance over very short distances. And obviously,
if an athlete can beat that record, they could improve
proportionally, so, for instance, riding in a pure oxygen
atmosphere would probably help. |
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Also this assumes a typical bike. If the bike was lightened
below UCI limits, that would help a small bit (not much,
even the lightest elite athletes weigh many multiples of
their bikes already). It might also be possible to lower
rolling resistance, but bikes are pretty good in that
regard, and most of the ultra low friction approaches
come at a serious weight penalty (e.g. air bearings). |
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In summary, I consider it extremely unlikely that human
powered vehicles will ever break 250mph (even without
wind resistance, say on a treadmill, and even with
performance enhancing drugs), and the speed of sound at
the peak of Everest is still in excess of 650mph. |
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Of course, as [not] points out, if you ride an a vacuum
(with a breath mask, say), any speed is exceeding the
speed of sound, but I'm going to say that's outside of the
intent of the original statement. Also, you still be hard
pressed to exceed the speed of sound in your riding
surface (as low as 88mph in soft rubber, but soft rubber =
much higher rolling resistance). |
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If we can figure out how to make dogs cycle, their VO2 max
is about 4 fold higher than a person, add oxygen, and a ball
to chase |
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" Yeah, discussions here do that, you get used to it ". |
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So I need a dog, a ball, and an oxygen tank on my bike? I mean, who can afford an oxygen atmosphere? Let's not even use the s word. |
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There is no force tipping the bicycle backwards. At most, there is a force retarding the rotation of the rear wheel, so I say again bollox. And I do think that this whole friction thing is massively over-rated. I think interference with steering and consequent loss of balance is a much more pressing issue here, and so a third time I utter my opinion, bollox. |
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If you stop a wheel dead, the object attached to it will
tend to attempt to continue the rotation. for the rear
wheel, that is an up and over tip. |
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And no speed would inherently cause you to lose balance,
so the only theoretical restriction on speed (in a vacuum)
is rolling resistance. |
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[Notation] Really not sure. Probably more in the tires, so
going to something like solid tires or even metal contact
might improve the numbers, as long as you had a
perfectly smooth floor, and enough traction that you
didn't lose the ability to steer enough to maintain
balance. |
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