Slashdot Mirror
Crowd Funding For Crank Physics
BuzzSkyline writes "A new design for bicycle cranks violates basic principles of physics, but that's not stopping the inventor of Z-Torque cranks from trying to raise thousands in start-up capital through crowd funding." The picture looks intriguing for a fleeting moment before it looks silly. Covered in similar style at a site I'm glad to discover exists, the Bicycle Museum of Bad Ideas.
Anyone who says anything against this cranky idea is probably some sort of whack job!
What are examiners for again ? Spelling mistakes ?
You seem to regard science as some kind of dodge... or hustle.
that it cannot be used to extract money from the gullible and hopeful -esp in America where the common man knows so much more than the engineer or the scientist...so in that sense it is a good idea just like all the weight loss and sex aid supplements you see on late night cable
-I'm just sayin'
because this guy will get funding and the beta testers WILL report that the new cranks have totally transformed their biking "experience"
...can quite comfortably fit outside it.
If computers were people, I'd be a misanthrope.
It's possible that by moving the pedal so the cyclist's legs are in a different position during the pedal cycle, it's possible that his muscles could more effectively power the pedals.
Except no change has been made to the pedal cycle...
The shape of the crank doesn't change at all as it's fixed. The same effect could be had by just going straight from the pedal to the place where it connects up with the gears. Moreover because of the extra metal involved you have to do more work in order to do a single revolution.
I'm too lazy to do the math, but this definitely makes it harder. That is unless he's managed to break the laws of thermodynamics.
And it does nothing at all for the inherent inefficiencies related to pedals having 2 moments of inertial.
One problem with long cranks and a low bottom bracket is the possibility of hitting your pedals on the ground during a turn.
This makes is worse by making it even more likely to hit the crank arm on the ground.
The alternative to limited government is unlimited government.
But the whole point is that as long as the crank is solid, its shape has no influence whatsoever on the transmission of force from the pedals to the gears. If the transmission of force between gears and pedals is identical, in turn, there is no possibility whatsoever of the layout having a physical (read: not "I have these magical cranks so I must pedal differently!") influence on the driver's posture.
Given this comment was made at all and subsequently upvoted, I suppose it's fair to say that even Slashdot is prone to falling for this...
...or wyse enough friend to tell him he's just plain wrong!
You're kidding, right? The Z-crank doesn't even do what you seem to think it does. I encourage you to invest your life savings in this, er, invention.
I've seen this before a dozen times or more as an engineering consultant. Some crackpot inventor comes in for a consultation with an engineering idea that "will save the world"*, and they say it works great with the soda-bottle-and-silly-straw model they built of the idea in their bathtub. They have $4 million in investment lined up, and they ask me to work up the numbers to show the feasibility of the idea.
2 minutes later, after trying to explain to them the 0th/1st/2nd Laws of Thermodynamics and how their device can't work because it violates all of them, it degenerates into a shouting match where the inventor (with an on-line PhD in cosmetology or similar) now is trying to tell me how the 0th/1st/2nd Laws of Thermodynamics do not apply to their device. I wish them luck and then send them to the door.
I don't envy them, because their options are 1) somehow continue to snow the investors until they make a major ass out of themselves when demonstration day inevitably comes and/or 2) slowly come to the realization that the 0th/1st/2nd Laws of Thermodynamics DO apply to their invention and that they somehow need to backpedal (pun!) out of the situation.
I'm not against garage inventors, but I wish them the humility to take 30 minutes to get their ideas vetted by a professional in the field before they make asses out of themselves and many others. There are many areas in engineering where the legitimate ideas are getting drowned out by the noise made by the uneducated hucksters.
*actual phrase used.
It's possible that by moving the pedal so the cyclist's legs are in a different position during the pedal cycle
Doesn't work like that. Draw a crank like this on a piece of paper, jab a pen through the point where the crank would connect to the gear and rotate the paper: you'll quickly notice that the thing still follows the exact same circular motion as any old, regular crank does, and therefore the legs don't actually assume any different a position during cycling. If the crank was displaced from the center then there would be a difference as it would no longer follow the same path as a regular crank, but alas, that's not the case here.
An analysis, found on their webpage:
http://www.z-torque.com/Portals/6/DrHuangReport.pdf
Claims that the benefit is from two side effects of the claim:
The increased mass gives a flywheel effect, meaning the pedal goes through top dead center easier.
The long shape bends under pressure, which does slightly increase the length of the arm under pressure.
So, by going to carbon fiber (lighter, and most likely stiffer), they'll most likely negate any benefits!
> so the cyclist's legs are in a different position during the pedal cycle
Only because of the bending. If it were stiffer, position would be exactly the same.
No, it's not possible. During the whole pedal cycle, the wheel is evenly in contact with the ground and the gears are in even contact with the chain. Throwing the angle on there doesn't put the rider's legs in a different position any more than rotating the existing cranks would because the "cycle" still results in the completely circular wheels and gears being in the same place. Simple physics is exactly why this can be dismissed.
"this can't be dismissed just because simple physics says that it has no mechanical advantage."
Are you high?
That's exactly what you can do. The whole point of this is that despite how the bar is shaped the pedal has NOT moved in relation to the crankshaft. If you DID move the pedal, that could make it more effective. It's called "a longer crank". Problem is your pedals tend to hit the ground if you do that.
The shape of the crank still makes no difference. Try mentally adding a straight crank superimposed on the Z-shaped crank, and this should be apparent.
> have to do more work in order to do a single revolution.
It's inertia. It's not wasted. It'll create a force when the pedal decelerates. Since you always want the pedal spinning, this isn't so bad for cruising. It's only bad for transients, which this would help smooth out.
> related to pedals having 2 moments of inertial.
Would be no different than a straight pedal with more mass on the end.
A variable length crank that grew longer or sorter and avoided ground contact would be a wonderful way to over engineer a bicycle.
You seem to regard science as some kind of dodge... or hustle.
It's possible that by moving the pedal so the cyclist's legs are in a different position during the pedal cycle
Doesn't work like that. Draw a crank like this on a piece of paper, jab a pen through the point where the crank would connect to the gear and rotate the paper: you'll quickly notice that the thing still follows the exact same circular motion as any old, regular crank does, and therefore the legs don't actually assume any different a position during cycling. If the crank was displaced from the center then there would be a difference as it would no longer follow the same path as a regular crank, but alas, that's not the case here.
Ahh right, I was lulled into thinking that it solved the no power at top-dead-center problem, but all it does is move TDC 20 degrees along the pedal cycle.
Can I get twice the funding?
It's called a 3d printer with PLA, and a technique called casting. Heck since one sode of this will be flat (ok, two sides,) you could probably do this with ABS plastic. Sure you need a software model, but you cnd probably frough one up fast enough in SketchUp, Blender, or even Corel Draw, simply knowing the requirements for mounting to the shaft and mounting pedals to it. And you'llprobalby have to tap the holes for securing each, but so long as your 3d Printer can handle the dimensions of a crank arm, you're golden.
Cast em out of aluminum, brush and laquor them, have fun with the custom cranks. Or if you're less concerned about weight, looks, durability, etc. cast em out of lead, gold, silver, platinum, use the abs print as a core for a carbon fiber build. Use the model to CNC them out of a block of stainless. Build a small mass driven generator into them and add LED's and an arduino to show of pretty lights, present a message as you're riding down the street, whatever.
You never know...
Automatically?
I think: "TIME CUBE"!
"Flyin' in just a sweet place,
Never been known to fail..."
but all it does is move TDC 20 degrees along the pedal cycle
No, it doesn't. The forces involved at the peddle and at the crank are identical to those if it were a straight connection. The only difference is the shape of the metal piece connecting them. TDC is in exactly the same place as it would be if there was a straight piece of metal connecting the peddle to the crank.
Who is John Galt?
Manual of Patent Examining Procedure; 706.03(a) Rejections under 35 USC 101 III A rejection on the ground of lack of utility is appropriate when ... (2) an assertion of specific and substantive utility for the invention is not credible. Such a rejection can include the more specific grounds of inoperativeness! Such as inventions involving perpetual motion.
You seem to regard science as some kind of dodge... or hustle.
The length of one of the elements is innecesarily longer than the final crack length. I bet it's a nighmare to pedal thru irregular terrain, collisioning with the ground every second.
It's inertia. It's not wasted. It'll create a force when the pedal decelerates. Since you always want the pedal spinning, this isn't so bad for cruising. It's only bad for transients, which this would help smooth out.
Well, just make the crank out of osmium then. Add some weights to the pedals. Problem solved.
But in any case, this can't be dismissed just because simple physics says that it has no mechanical advantage.
Ok.
If this crank extends the diameter of the rotation
Just making the crank longer would do that. The shape bears no effect on the diameter of the rotation as long as the distance between the pedal and the axle stays the same. The shape would only bear an effect if the crank dynamically changed shape during the rotation, but alas, this is a fixed construct.
You decide.
I wonder if the report as a "Scam/Fraud" has an automated threshold for removal of a certain fundraising video on youtube:?v=O-WN8kPolug
Yes ... except the spring constant of the crank has been changed. What I can't figure out by inspection of the photographs alone is if the change would be sufficent to explain the perceived differences. As you pedal around that nice, big L shape is going to distort slightly, even though it appears to be designed not to, storing some energy by folding up a wee bit during some parts of the cycle, and releasing it by unfolding during others (or vice versa). Or heck, maybe it opens up, rather than folds in. At first blush, it probably isn't a big enough effect to explain things, but an L-shaped crank is going to tend to be more flexible than a straight-arm crank.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
It's possible that by moving the pedal so the cyclist's legs are in a different position...
Can you please send me some of the stuff you are smoking?
There are fewer illiterates than people who can't read.
A bicycle is a simple machine. Simple machines work by reducing the force necessary to complete a task. This is mechanical advantage. For a bicycle this mechanical advantages are created by the radius of the pedel and the ratio of the gears, usually with a big gear radius in front, and a smaller gear radius in back. To start the ratios are larger, then can become smaller as the bike accelerates.
There is another thing. The effective force is only the component that is perpendicular to the direction of motion. That why you normally start with the pedals parallel to the ground, and the rider pedaling straight down. With normal pedals, the force is transmitted directly to moving the crank. With this style, some force is always going be expended torquing the z pendal, which will eventually lead to the seam to fail.
"She's a scientist and a lesbian. She's not going to let it slide." Orphan Black
Really? Slashdot can't even understand something that would be taught in week one or two of high school physics? Doesn't anyone remember the calculations for torque and how when "johnny" ties a rope to the end of the wrench and pulls on that for "torque", it doesn't actually change anything?
Also, this has been all over the internet quite literally for months. Slashdot is getting this story after it is how many months old?
Grandpa: My Homer is not a communist. He may be a liar, a pig, an idiot, a communist, but he is not a porn star.
Yeah but the inertial difference would be some infinitesimal amount. Way to small to notice. The real problem is that this design in going to suffer huge stress at the points of the Z so if our intrepid rider is into mountain bikes he's going to break this thing about 4 weeks after he starts using it at precisely the worst possible time to have you crank break (while standing on your peddles on a steep climb.)
All you have to do to blow this out of the water is ask him why there isn't a curlicue wrench to give you more leverage in a tight place... not like we haven't been using wrenches for a while. This is a profound DUH, and no magic fairy dust nor faith in a loving deity will wash the stink of stupid off it. Sorry.
The weight hanging forward off the top arm is balanced by the weight hanging backwards off the bottom arm.
Give up. It's useless. A crankshaft is a crankshaft no matter how curly you make the shank. Well, if you make it curly enough it starts becoming springy, but that's it. Why not get into the old 1970's fad of having elliptical gears instead? At least that did something.
Yes, and the flexing of the arm will certain end in the thing breaking at a stress point and potentially injuring the rider... we call this a SNAFU!
Are taxes on the stupid a bad thing?
New bad ideas can be patented. It isn't supposed to be possible to patent old bad ideas. The problem, is that old bad ideas are often badly documented, because they are bad ideas. If the patent examiner doesn't find the prior art in the limited time available, then the examiner is likely to grant the patent.
How often do you get to discuss a crank with a crank... too bad its not April, I'd have gone with the prank crank thanks.
What happens with this design if the pedals are at TDC and BDC, with a weight hanging off the top pedal? It should go forward as that is the direction of the "Z" arm. By my understanding that is one of his design goals, to eliminate the dead spots as with regular straight arms in the same situation nothing happens (you would need forward motion to move the arm).
No, no it won't go forward with balanced weights on each equal-length lever attached to a pivot in the center.
The #$#@ dead spots are STILL THERE, they just happen to "look" like they are in a different place.
Grandpa: My Homer is not a communist. He may be a liar, a pig, an idiot, a communist, but he is not a porn star.
Oh come on. I'm not giving my money to anyone who can't write a sentence.
----------
Any problem can be made unsolvable if there are enough meetings made to discuss it.
I always slow way down when the guy up front is farting. Don't have to breathe as much of it that way.
Trust me, when you are constantly breaking wind
If you are constantly breaking wind you should either change your diet or go see a doctor.
Hmm, subtle pun or can't spell??
Mostly random stuff.
this can't be dismissed just because simple physics says that it has no mechanical advantage.
Actually, that's exactly why it can be dismissed. It's nonsense.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
They basically dog leg the peddle arm and claim there's an advantage. I thought it was linked in some way so the length changes during a stroke. It isn't even that clever it's just a pointless waste of aluminum. Even a variable length one wouldn't work because it'd throw off you rhythm. Bicycle peddles haven't changed much in over a hundred years for a reason.
Whoa, OK, I misunderstood that for a moment.
*** "Freiheit ist immer die Freiheit des Andersdenkenden". -- Rosa Luxemburg ***
If you read one of the papers, from Florida Atlantic University, referenced on the site, the author claims that the advantage comes from an 'intrinsic favorable flexure mode." Basically, he is saying that the flex at the joint of the Z shape creates a smoother ride and higher torque at specific angles (not peak torque however).
While I find it unlikely that the effect is as positive as stated in the article, it is plausible that there is a small second-order effect due to non-rigid behavior of the crank. It is claimed in the article that this effect was tested independently, however I can't see how a flex in the pedal would produce any other effect than to steal energy away from the peddler.
Besides, if you want more torque while biking, just use clip-ins.
Judging by the photos, it appears that the Crank with Z-pedals has a larger Moment of Inertia ( http://en.wikipedia.org/wiki/Moment_of_inertia) than the Crank without Z-pedals.
Perhaps that increased moment of inertia has a flywheel effect that helps ease the pedaling? I wouldn't expect it to make a difference, but then again bicycle racing is so incredibly optimized -- just look at those stupid looking helmets bicycle racers wear to improve their aerodynamics -- so perhaps the riders can tell the difference.
First thing you should do is ditch the cranks that came with your bike, and find some 175 or 180mm cranks instead. You have the longer legs required to use them, after all.
Hal Spacejock: Science Fiction with Nuts
Just take a look at those infomercials that try to tell you that 1) for your entire life you've been wobbling around about to fall over
The solution to that is to become a Weeble, because Weebles wobble but they don't fall down.
The crankarm is likely just a distracting gimmick to confuse people. The real secret sauce would be putting planetary gearing inside the bottom bracket to give the rider heaps wider gear ratios without any extra chain or unwanted chan slop. Combine that with an existing two deraileur system driveline, and you could climb hills and scream on downhills like nobody's business with fairly normal tooth ratios on chainring and gearset and have no worries about throwing your chain.
Physics violations? Derp... Look closer.
At least that's what I'd suspect.
The Z-crank doesn't work due to basic mechanics. The various warp-drive and wormhole designs are usually not provably impossible, though it is very unlikely that they work (due to quantum effects), and require material (negative energy density matter) that probably can't exist in the required densities, and typically need engineering on a difficult to imagine scale.
In other analysis, 'Smoother pedaling and more power then old standard type cranks' - I don't think this means what he thinks it means.
One measly zig? That's not going to efficiently couple my torque rotation constant. I want a crank with a minimum of five zigs and, for fuck's sake, a bare minimum of *three* zags... and that will be the "intro" model. The "pro" crank will come with seven zigs and five zags. The "custom" option will end the zigzags with a loop.
Throw in enough, and the bike will basically pedal itself. All I need to figure out now is how to perfect my shake weight handlebars. Still having problems with the braking on those things.
So, by going to carbon fiber (lighter, and most likely stiffer), they'll most likely negate any benefits!
Actually, carbon fiber is more flexible than aluminum, so it would flex more. But flex is bad, not good. The ideal crank would have 0 flex, so as to transmit 100% of pedaling energy, rather than wasting it through flex.
FYI, If my time at the gym bro-learning meat-head science is worth anything, than cycling is a very inefficient movement since it overrides the hamstring which counts for over 50% of the leg muscles.
If you do it right, you use your hamstrings. They kick in toward the bottom of the stroke, and pull across the bottom and up the back.
> A new design for bicycle cranks violates basic principles of physics
At first I was prepared for a crank out of MC Escher, that couldn't exist in the real world. But it's just snake oil. Sigh. In a Kevin Kline voice; DisaPOINTed.
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
Ummm... don't most 5-year olds learn to eliminate dead spots by just, you know, having a bit of momentum? Moreover, the cranks in any engine have dead spots. There are motorcycles with ONE cylinder. Huge dead spot, right? Not a problem. Momentum. That's the whole deal with these systems. Dead spots are just not a problem. Most of you couldn't stand straight on the crank if you tried, and if you did, the momentum would carry you through in the proper direction after one good stroke.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
How is this different from alleged gurus claiming that foo-oriented programming is a silver bullet and selling books, seminars, special languages, methodology consultants, and so forth without first having objective evidence?
It's not just bicycles.
Table-ized A.I.
Quantum physics trumps /all/ forms of logical thinking.
If I have been able to see further than others, it is because I bought a pair of binoculars.
This guy almost got me to tie up $1 on kickstarter, but plenty of other people covered the comments.
Flex isn't bad. Flex where the flex is changed to heat? Oh, that's a loss. If you can flex without heat, you don't get loss (ideal spring).
Learn to love Alaska
You don't have to just have the effect of changing the crank length. Offset the crank 30 mm from the center of the chainring. Aim it so that the shorter crank is on the downstroke. You'll get an equivelent of a smaller chainring, without having to change the chainring size. Or reverse the offset for the opposite effect.
Learn to love Alaska
And they go to extreme efforts to reduce it. Muscle strength spent flexing the crank is wasted.
Same thing for crank weight. They go to extreme lengths to shave grams off their bikes, and even more to reduce weights of moving parts.
The idea that this is a great, new, magic crank because it's flexible and heavy is ridiculous!
Prediction for end of Universe #42: Fencepost error in Quantum_bogosort.cpp
That might be relevant, if this design had any effect of moving the pedal so the cyclist's legs are in a different position during the pedal cycle. But all an angled crank arm does is give you a heavy crank that takes up more space to put your legs in the same position as they would be in with a straight arm that had the same length as the straight-line (rather than along-the-bent-crank) distance between the ends of the crank.
I suppose. If you could magically have a weight appear only off the top pedal's Z-arm when the pedal was at TDC. (Note that such a magical weight would also give you a perpetual motion machine, since you could set the pedals at TDC/BDC, and they would start accelerating on their own and continue to provide power with no effort.) Of course, if you had such a weight only off the bottom pedal's Z arm, it would go backwards. Or, if you just had the weight from each pedals Z-arms, without magical weights that appeared on one or the arm in a given position to help or hinder, they'd cancel each other out, and you'd have dead spots, which brings us to:
Even the inventor's website expressly acknowledges that the Z-torque crank has the exact same dead spots as any other crank (of course, he doesn't mention that this exactly the same as any other crank), saying:
So, no, even the crank making the crank doesn't claim that the crank eliminates the TDC/BDC dead spots inherent in any crank.
Right, exactly, its not.
Right. The differences are:
It's possible that by moving the pedal so the cyclist's legs are in a different position during the pedal cycle, it's possible that his muscles could more effectively power the pedals.
Except no change has been made to the pedal cycle...
Exactly. The easy way to think of this is this way:
Weld a piece of straight metal onto this thing from the pedal to the center of rotation (just like a normal straight crank) so you have a "triangle like" assembly. Now pedal. See! Mechanically, it's the same thing. (Except a little heavier and a lot stronger.)
Now, saw away the Z-Torque crank. See. Same thing again.
This assumes the Z-Torque crank is inflexible. If the Z-Torque is flexing, then it is absorbing some of the the rider's energy and turning it into waste heat. (Until it fails.)
The increased mass gives a flywheel effect, meaning the pedal goes through top dead center easier.
[...]
So, by going to carbon fiber (lighter, and most likely stiffer), they'll most likely negate any benefits!
Here's the thing: carbon fiber does not have to be stiff.
You can go out today and buy carbon fiber leaf or coil springs.
carbon fiber cranks are nothing new to the (off)road bicycling word.
And haven't you heard about the amputee athletes who run on carbon fiber legs?
But the main reason for using carbon fiber is lighter weight, and if your system depends on extra rotating mass,
then there's absolutely nothing to be gained by making the crank out of super light carbon fiber.
If Mr. Z-Crank wants springier, he can just choose a different metal alloy and keep the same mass.
[Fuck Beta]
o0t!
FTL and warp drives are an open problem with no good designs in mind. This pedal is a specific design which obviously does not work.
This inventor has apparently managed to duplicate the invention of medieval alchemists: Transmuting gullibility into gold.
Once upon a time, I had a wall-mounted coffee mill of high quality and life-long quality. Every one to two years, I'd be sending in the crank handle because it had broken off. It was some cast material, granted, but the main problem was that it had an S-curved design and consequently stress points that were not really dealing well with discontinuities in the mechanical resistance of the coffee beans.
The curvage of this Z-crank is way worse. With forged steel, it would likely be manageable to avoid stress-induced breaking at reasonable weight. However, the material looks like aluminum. It would likely just snap eventually, with a life time significantly shorter than that of a straight crank.
No, it just trumps intuition
The guy uploaded the analysis from a professor of Florida University which notes improvements over regular cranks... However, not the ones claimed in the video.
What is nice is that the first paragraph contradicts the video : "As far as mechanical advantages is concerned, the angle crank does not offer any more than the traditional straight-link crank[...]". The Pr sees the higher momentum of inertia as beneficial for pedalling as well as the bending mode, concluding that those two properties are obviously not intended.
As far as I am concerned I am not quite sure I would like to have more momentum of inertia to overcome and I find the effective improvement from flexure mode dubious.
The crank has a BEND in it BUT for physics it is a perfectly straight crank, a direct line from the pedal join and the center of the gear. It therefor does NOT change the position of the pedal in the circle of movement despite how it might appear. 0 degrees and 180 degrees is STILL the pedal being at the top OR bottom regardless of how the metal of the crank zigzags.
Somewhere else it is suggested that the extra material creates a flywheel effect. In theory, this is true but since ANY crank has weight ANY crank will be in object in motion that stays in motion until an opposite force stops it (the friction of the rest of the bike). And if the extra weight is what does the trick, why make it out of aluminum (the currently selling model) and the new one out of carbon? Make it out of cast iron, inlayed with lead.
Perpetual motion machines usually have some kind of charming "but it should work because it looks cute" aspect but physics ain't cute or charming, it just is. But people who believe in beards in the sky, karma, justice outside a court system, democracy are always looking for the fantasy to beat reality.
THe whole "dead" points while cycling by the way only happens in extreme cases where you are standing on the pedals and encountering a lot of resistance. In normal daily cycling the sheer weight of your leg, the motion will just continue smoothly on.
This crank solves an issue that isn't there and doesn't solve it either.
Oh and if you fit it on your bike, you just lowered the ride height of your bicycle, enjoy scraping them across the ground in corners.
MMO Quests are like orgasms:
You may solo them, I prefer them in a group.
But not likely. Nearly all examples of flexing do convert energy into heat. For bikes, you usually want components to be as stiff and as light as possible.
The only way I can see crank flex helping would be to try to even out the force applied whilst pedalling, but I don't see how a crank deforming would help with that. The usual way to try to even out the pedalling forces is to use an ellipsical chainring, but they're not very popular due to the extra metal/expense/weight and not much advantage.
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
Why dumping into the braking system? you are just wasting energy obviously you brake if you have too, but good planning means you do not need to brake so often or as hard.
When i am driving I usually leave a reasonable gap in front of me. when the car in front of me brakes i just step off the gas and my car slows down the gap decreases till i match speeds again. I use less fuel since my fuel is concentrated into covering distance not moving as fast as I can at any given point. Steady driving is fuel efficient it is acceleration and deceleration which are big users of energy.
Blarney Quality Restaurant, Plants
So that I'm always cycling downhill.
If you were blocking sigs, you wouldn't have to read this.
There almost certainly are. I know I have some curved wrenches in my collection, although it's tough to tell whether the curve is intended to be decorative or functional.
If you go back to the late 1800's there was a proliferation of tool patents for all sorts of weird shit for supposedly functional reasons. Every second blacksmith, carpenter and hardware store owner had an idea for building a better hammer, handplane, tape measure or wrench (or possibly a multi-tool combining all of the above) and ran it into the patent office ASAP. Most of them were overcomplicated bunk, but there were probably a few good ideas...
Log in or piss off.
No, there's absolutely no difference.
If you were to trace the position of the foot relative to the bottom bracket (centre of the chainrings), then your foot would trace out a circle. You can get the exact same pedalling motion by making a straight crank (which would use less metal, be more rigid and lighter).
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
well, TDC is the same place for the foot, but there is a bit of weight in front of the crank that can "help" get the thing moving ( assuming we are at a stop, and the idiot rider has the pedal at TDC). YAY, easier ( and bullshit)! Of course, any time you carry extra weight on a bike you have made a mistake. I want to make the next wonderful product in this line of snake oil, but instead of the crank, I will put weights on the toes of the shoes. When you have the crank at TDC, the shoe will use gravitational potential buzzwords to convince dumb people to make me rich to reduce the PERCEIVED effort.
lolz, you would have to push down on the upstroke to compress this. There is a graceful solution to this in place already. The pedals clip to the shoes. The rider simply pushes the foot into a position past TDC and BDC, then simply pushes down/lifts up. there is less pressure during that small moment , but the muscles dont work efficiently through that movement anyhow. Any mechanical fix would require a biological change to use to its fullest extent.
You miss my point though. I understand that your foot is making the same motion, and that you have the same mechanical leverage given the distance between your foot and the gear center.
However, the angle at which the crank connects to the gear is now shifted from the angle between your foot and the center of the gear (relative to horizontal). In a simple free-body diagram, this also makes zero difference, as the angle of connection does not affect torque. But since the crank actually connects at various points along the bolt, the angle of connection could determine the direction of force at these various connection points. This of course has absolutely nothing to with the z shape, and the same putative effect could probably be achieved simply by changing the shape of the connector. Thus I'd agree that that extra metal going into the elbow of the angled crank is really doing nothing.
So all I'm investigating, in thought, is how the time-varying direction of forces applied during pedaling may be shifted depending on how the crank connects to the gear. If you are inclined to believe any of the data produced by this dude, which I realize is suspect, then this graph (available in their gallery) presents data qualitatively in line with my reasoning, and, interestingly, NOT in line with their reasoning (which I think we both agree is grossly incorrect). I'd further note that if I were making up data to fit their explanations, I'd have put in some at least small magnitude changes, not just a phase shift as we see here. So is it possible that there is some (probably very small) effect of angle of connection?
Lastly, what does a phase shift do for total work? Nothing for a given amount of force, I think. But that's where biomechanics (OP) comes in; since the leg isn't equally efficient at all pedal positions, this phase shift could result in a change (positive or negative) in total efficiency.
Again, not a mechanical engineer. I'm just speculating on what could cause differences that might not show up in a simple physics model. All models are imperfect, so I'm trying to challenge the model assumptions. Does this make sense, and do you agree that this is a different issue than you present in your rebutta to my post?
Curved wrenches are for awkward bolt placement.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
... features Lotus Notes and a machine gun.
It is the finest available.
See you space cowboy
Flex isn't bad. Flex where the flex is changed to heat? Oh, that's a loss. If you can flex without heat, you don't get loss (ideal spring).
You mean if you could flex without heat you wouldn't get heat loss. But you can't and you do.
This thing DOES work to reduce _perceived_ pedaling torque. Everyone on here is bringing up the trivial physics issue that torque is the same - believe it or not, that's NOT THE POINT.
The point is that this pedal's design advances the angle of the rotation cycle by 15 or 20 degrees due to the kink. That means at the TOP of the pedaling cycle, the cyclist now HAS leverage from a downward push on the pedal. Normally, at the top of the pedal cycle, you get ZERO leverage from pushing down. You have to normally push 100% forward at the top of the pedal cycle (because the pedal axis is pointing perpendicular to the ground and pushing down pushes you into origin of the wheel). Pushing forward at the top is much harder (think about it - it's a weird angle and you have restricted muscle leverage up there) than being able to push down with your whole gravity-assisted body weight. This design shifts the deadspot from the normal 0 degree point at the top of the cycle to a point further down where momentum is presumably easier to deal with.
It's like everyone on here gives themselves a medal for understanding physics 101 without actually taking a look at the effective biomechanics of the situation. Torque being the same does NOT equate into a similar pedaling experience. The offset rotation is the selling point of this thing. People should try it before commenting.
and you have a winner!
No, there is no inherent loss of leverage at tdc in the crank, the loss of leverage is in the piston (leg) That is turning reciprocating motion into circular motion.
It is the position of the crank arm to the piston (leg) that gives the flat spot in power.
If I replaced the piston (leg) with an electric motor who's axis matched the bottom bracket, then made and arm that reached out to attach to the pedel, there would be no loss at Tdc or anywhere else.
It would look stupid and require a fixed point to mount the motor on, but I hope you see my point, it is the tdc of the piston, not the crank, that makes the tdc flat, and that does not change with a whacky crank shape.
Never answer an anonymous letter. - Yogi Berra
More simply: the TDC is a function of the piston, not the crank. The piston(leg) has not changed, so tdc does not change.
Never answer an anonymous letter. - Yogi Berra
Springs only return power when there is one fixed point, like a pogo stick.
With the crank and piston setup, springs don't return the energy, they dampen it.
That is why motorcycles have something called a Cush drive, it is a spring or rubber buffer loaded gear that helps reduce the kick/lash produced at ignition from thrashing the gears and rider.
This is especially important in a 2-stroke Vespa, the Christmas tree style transmission is exceptionally prone to shattering teeth if the Cush drive springs break.
Never answer an anonymous letter. - Yogi Berra
Abysmal ignorance can be pretty interesting, to be fair. Sort of like watching chimpanzees throw poo at each other at the zoo.
It is really kinda sad.
Even an average bike with decent bearings is 95+ efficient, with a little loss to the inefficiency of the freewheel and friction in the bearings.
A high quality bike pushes that higher, and a fixed gear bike with no freewheel and no variable gearing reaches 98.5 percent efficiency.
Getting at that last 5% is hard, you are better off improving your form or your aerodynamics if you want more efficiency.
Never answer an anonymous letter. - Yogi Berra
This is all easily explained by one simple mistake: you are looking at the wrong crank. There is one, funny shaped crank in the video that seems to be strangely effective at extracting more work (in the form of money) than it should. Unfortunately it's also the one giving the sales pitch which may be where the confusion arises.
Sorry, that doesn't make much sense to me. The angle that the crank connects to the chain ring would only be relevant if the chain ring is non-circular or the crank doesn't connect to the centre of it.
However, as the chain ring is circular (for every bike that I've seen), it doesn't make any difference at all. Splined cranks can be mounted at a variety of orientations with regard to the chain ring, but the only difference it makes is if you don't mount the other crank at 180 degrees to it. Sometimes people will rotate round the chain ring when it gets worn out as the wear won't be even due to the different forces related to the pedal positions
The only time you're going to effect the biomechanics and efficiency is if you change the crank length or go to a non circular chain ring.
I ride a unicycle as well as a normal bike and on a unicycle the crank length is more crucial as it affects the gearing (which on a fixed wheel unicycle is related to the wheel size). Again, though, a "phase shift" will only affect the wear on the wheel/tyre and not affect biomechanics at all.
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
this is achieved using oval shaped gears
Really? Slashdot can't even understand something that would be taught in week one or two of high school physics?
At least in Canada moments of forces are no longer taught at school. They may get some basic archimedes lever-style principles but the first time students see proper rotational dynamics with moments of forces is when we teach it to them in a first year introductory physics course at university. Even AP physics B skips this stuff - you have to do physics C - so I imagine the US is the same.
You didn't read the paper.
The paper debunks that the shape has anything to do with magic and clearly states the shape, on it's own, does nothing in the first few paragraphs. Even with the increased length for part of the revolution, I assume if you integrate over the whole downward push, for both, you would get the same numbers.
Haven't ridden a bike hard since I was young. But I do remember the blisters on the inside ankle joint. Mebbee a canted angle relieves you of that worry, so you can pedal .001 % harder.
Listening to this discussion reminds me of the 'Airplane on a Treadmill' internet debates from long ago. There are 2 sides to this discussion and (at least) one side is not listening to the other. As I see it:
Side 1 The Z-crank is a simple change in geometry from straight crank arms. If you assume a rigid body, then the shape makes NO DIFFERENCE to the torque/energy transfer characteristics. The larger mass will likely have a higher rotational inertia and an increase in total bike weight, but these effects are assumed negligible for the purpose of this discussion.
Side 2 These folks assume the crank is not rigid, yielding some spring energy storage at certain positions in the crank rotation and giving it back when the cranks is in a different position. It is quite plausible that this happens, the question is: Is this energy storage significant and beneficial to the rider.
It would be nice to see arguments on the relative merits of each and do away with all the finger pointing.
Supposedly.
But some of the really old implement wrenches are so short and ornate (i.e. multiple sizes per end, practically multi-tools) that I'm not sure the curve could really provide that much function. For all I know, it was as much for identification or some obscure metal-casting purpose.
Log in or piss off.
I've never heard of a crush drive, but from what the Internet tells me about it (other than how to replace it) is that it's commonly a spring system to absorb gear-change shock. Nobody mentioned ignition being involved. That means it absorbs the shock, and likely releases the energy shortly after absorbing it.
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Quoted directly from their website (http://z-torque.com/Video.aspx):
Results: Participants achieved similar maximal oxygen consumption, peak power outputs and gross efficiencies with the Z-Torque and normal crank configurations (Table 1). In addition, ratings of perceived exertion (RPE) at 150 and 200 W, heart rate (HR) at peak power output, 150, and 200 W, and cadence at 150 and 200 W were not significantly different. However, participants perceived their effort to be significantly lower at peak power output with the Z-Torque crank.
--
So it's a placebo. Or Nocebo, depending. You believe the pedals make it easeir, so it feels easier, but it's exactly the same.
And why is there that shock?
Because of the torque created at the moment of ignition. Nothing to do with the actual ignition system, I said "at ignition", meaning the fuel air mixture burning and creating energy. All the power the engine is going to produce is made in that instant, and it is distributed through the stroke until the exhaust valve is opened, or exposed in the case of a 2 stroke Vespa.
The cush drive dampens it, but there is lossage, although not enough to care.
Downshifting it does reduce some of the lash as you re-engage the clutch and momentum from rear wheel tries to drive up the RPMs of the engine.
But hey, you read the internet, I just rebuild Vespa engines for a hobby and have access to people that do it for a living.
And I have never heard of a crush drive either.
From a physics point of view:
Unsupported springs act like 2 equal mass balls in a vacuum attached by a spring. If you load the spring and let go at the same instant, the two masses will oscillate, but the center of mass will not move, thus no work is actually done. Eventually the masses will stop oscillating from entropy (heat) created in the spring.
Fix one of the masses against an immovable object and now the spring will do work.
Since the Vespa, nor the bicycle, is a mass in vacuum, the springs do push against either the wheel side of the drive, or the engine. But the energy returned is nothing like the energy used to compress the springs.
Never answer an anonymous letter. - Yogi Berra
What has that got to do with the article? Or did you just spot an opportunity to try come off as knowledgeable about cycling?
My other UID is three digits.
http://z-torque.com/About/TheInventor.aspx
(subject line punctuation left as an exercise for the reader)
Any chance of elastic deformation giving a boost? cranky crank?
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It was a dark and drunken night. Four shots called out -- drink me.
But there are ratchet wrenches where you have limited room to swing the wrench so some mechanisms allow a minimum of five degree rotation before you can move it back for another turn. Why can't bicycle pedals just ratchet up and down instead of rotating? In a turn just short stroke the inside pedal so it wont hit the ground while still making a full long stroke on the outside. Reversing gears can be included so rotation is maintained on the upstroke with toe clips. No dead spot on the top or bottom of the stroke like there is on rotating pedals. I have never seen this (except on screwdrivers) so I claim the patient for it's use on a human powered device.
It doesn't violate the principles of physics. It works exactly as the physics determines it should. What it does do is take advantage of people's misconceptions and ignorance of physics.
It's the old story of more money than sense, or to be more accurate, the (almost as) old story of taking advantage of people with more money than sense.
One of the universal rules of happiness is always be wary of any helpful item that weighs less than its operating manual
Back in the late 70s one of the bike mags had a piece on an Italian company who were marketing a beautifully made crankset with right angle bends in them.. They weren't impressed with the idea then, either.
Now, as to the efficacy of oval chainwheels.....
Star Trek transporters are just 3d printers.
So let me get this straight - the more zigzags the crank has, the less effort? How about a dragon curve crank? It could be made out of paper, since the pedalling would be so easy it would exert hardly any pressure!
... I actually had this same idea several years ago. Then I built a simple prototype out of wood, tested it, and saw that it didn't do squat. Apparently my second thought should have been, "Don't test it, just build it and charge money for it."