Longer lasting cush drive material available

[dlaing]

I'm still convince my statement is correct. It was qualified by "theoretically". Of course the peak torque would not be infinite in the real world! The key point is that I did not assume the only elasticity is the cush. If you read my statement carefully, you will see I assumed no elasticity. No means no!

 

In the equations to calculate the peak torque, the rotary inertia of the bike will be in the numerator and the time it takes to transfer the engine's energy to the bike will be in the denominator. The rotary inertia is more than zero no matter how much the bike weighs, unless all of its mass is in a single point, which is absurd. If there is no elasticity in the driveline (and just in case you think of it, none in the tires either, which I consider are part of the driveline for the purpose of this discussion) then the time is zero, and the result of the calculation something divided by zero, which is infinity.

I disagree.

With no give of clutch, tire, or driveline, the finite inertia resisting the lifting of the front wheel limits the torque at the rear axle to the finite universe.

So in both the theoretical and real worlds, the torque will be finite.

And more relevantly, the lighter the front end and the higher the gravity, the less the torque will be at the rear wheel.

If you put a chromed steel front wheel on the front with disk rotors made of tungsten, you would get more torque than if you replace the front wheel with a nice carbon fiber wheel with ceramic rotors.

Infinite only occurs if there is absolutely no give. Inertia has a giving point that keeps the torque in the finite universe.

[Guest ratchethack]

OMG. I can't take it anymore.

 

But no, I'm STILL NOT goin' wadin' today! And I'm certainly not wearin' the ol' croc hat today, either!

 

Today, I've got me a nice little bass boat here, and I'm only venturing out into the vast, trackless Swamp o' Confusion just far enough to retrieve a few shanked drives for those who've got themselves way way off the fairway. I'm not particular about who's ball I find, and I'm watching and listening very attentively for crocs the whole time. First sign of a croc, I'm runnin' this bad boy up on the beach with me chestnuts intact.

 

Once again, I'm no mechanical engineer, nor am I a materials engineer. But I've been around the block a few times with heaps o' things mechanical from a shade tree mechanic's perspective, I'm at least partially grounded in both the fundamental sciences and practical mechanics, and I've read and studied enough to recognize when I'm in over me own head! By observation, I can also pretty well gauge when others have waded in over their heads -- occasionally, even when they can't seem to see the swamp f'er the mangroves whilst in way past their eyeballs. . .

 

Great Gertie's gallopin' garterstraps! What, exactly, is the point of all these endless, increasingly bizarre, and other-worldly cosmic calculations and spectacularly specious speculations?!?!

 

Coupla thoughts.

 

I see no value wotsoever in determining the "peak torque" possible to generate at the cush drive! Correct me if I'm wrong, but no one has as much as identified wot "peak torque" means in the context o' this err, discussion. . . But by any stretch of any definition I can conceive of, this is not only pointless, but it's not possible to determine with either consistency or accuracy anyway. But wot COULD this possibly tell us that's of value to consider WRT designing a "better" cush drive -- which, after all, seems to've been the "objective" (misbegotten or no) since the beginning of this little Klusterfest Koagulation without end?

 

Let's just take a hypothetical and say that we can arrive at a "median" peak torque figure for the failure of the driveshaft, and that this is the weakest link in the driveline. Now what does this tell us about how to correctly design a properly functioning cush drive?? NOTHING!

 

PLEASE CONSIDER:

 

What are the desired design parameters of a properly performing cush drive? I submit that successful recovery from application of peak torque (by any conceivable definition in the context of this thread) is far from chief among them -- and yet, this is ALL that's been discussed endlessly for pages here! After all, steel blocks will "recover nicely" from application of "peak torque" that would cause failure elsewhere in the driveline -- yet wouldn't protect the driveline in the slightest!

 

If the primary objective of a cush drive were to "withstand" peak torque, I submit that either of Dave's alternately described "chrome-moly hard" or "door-jamb soft" drive blocks would do quite nicely -- as would countless other kinds of material compounds that would make for a simply horrible and innefective cush drive!

 

Now one might reasonably ask here what would be considered examples of a "failure" of a cush drive? I submit that "collapse" with inability to recover from forces applied to the blocks would be possible with many kinds of materials, but not in the case of the stock or drilled blocks, because to our knowledge, there have never been any examples of this in the entire history of Guzzi V-twin cush drives!!

 

I submit to you, Gents, that the chief design objective of cush drive blocks is protection of the driveline (clutch hub splines, U-joints, driveshaft splines, etc.) -- NOT protection from peak torque wotsoever (however one chooses to define this), but rather protection from wear sustained over time by constantly repeated shock loads of far less than "peak torque" inputs -- shifting, on-off throttle, driveline slack between transmission dogs and muffs, clutch action, power pulses of the motor, etc. -- in other words, the cumulative effects of thousands of relatively small torque spikes and irregularities on the driveline, if you will -- NOT from anything to do with impact loads associated with peak torque!

 

Leave us not indulge in HYSTERIA here, Gentlemen!! Rather, leave us consider HYSTERESIS!

 

Chief among all design parameters of the cush drive, then, is proper hysteresis of the material compound. Perhaps not so coincidentally, hysteresis is a primary design parameter of tires (also a highly complex, highly engineered compound based on rubber)!!!

 

That's right -- setting aside lesser, but still very important considerations such as durability under not only the full range of operating torque, but under the petrochemical and temperature environment in which it operates, a cush drive requires a material compound with properties that above all other considerations, retards the effects of changing forces acting upon it, which will serve to soften, absorb, modulate, mitigate, ameliorate, and offset (where's my Thesaurus) the normal, constantly hammering, driveline "spikes" of relatively small shock loads from the transmission output shaft through the bevel drive, to the rear wheel.

 

As I've suggested from the beginning of the first thread on this topic, there are enough complexities of desired design parameters involved here, that attempting to come up with a "better" compound than either the stock or drilled cush drive blocks is more than a bit of a "shot in the dark" from the get-go. Certainly many theoretical predictions of pursuing a start-from-scratch "better" design would be expected to instantly fly out the window in practice, and much experimentation and field testing would be in order. Starting from scratch, you'd be lucky to get within the same ballpark of the desired hysteresis achieved with the stock blocks, let alone match the superior hysteresis of the drilled blocks -- and then withstand durability requirements of many many years in use at the same time!

 

Now that I've collected another bucket o' balls, this neck o' the swamp is looking way too familiar, and I've once again found meself way way past aghast and agog in the ol' Swamp o' Confusion. . .But I'm still not goin' wadin'!

 

Oh-oh. . . I just heard sumpin' big hit the water around the bend. Sounded like a croc hittin' the bottom of his slide. Nope, won't be reachin' in for that last ball after all. . . I'm outta here.

 

Wading too deep in the Swamp o' Confusion

takes a serious toll on the Naive and Foolish

[Skeeve]

Leave us not indulge in HYSTERIA here, Gentlemen!! Rather, leave us consider HYSTERESIS!

 

Chief among all design parameters of the cush drive, then, is proper hysteresis of the material compound. Perhaps not so coincidentally, hysteresis is a primary design parameter of tires as well (also a highly complex, highly engineered compound based on rubber)!!!

 

Not contesting the rest of your post, 'Ratch: I've been kinda sitting over here quietly chuckling to m'self over all the nonsense that's been issuing forth on this topic, but not so much as you, I expect!

 

WRT hysteresis, I think we would ideally want something w/ less hysteresis ("H") than rubber [which is known for being a high H material, generally], since the greater the hysteresis, the greater the energy lost to heat from H during the cycle. And heat [along w/ oxidation, something a well-greased set of cush drive wedges will be somewhat protected therefrom] is what kills rubber's flexibility. Hence the interest in alternative materials like urethane compounds, which are generally known to be more heat & oxidation resistant than common neoprene-type rubbers [but I cannot comment on relative traits of H, since I don't know.]

 

Resilience, plasticity, deformability are all properties that will be of value in a cush drive, to remove the f/x of sudden loads on the driveline and spread out the forces over time. Hysteresis (to my admittedly imperfect knowledge) is related to the loss (or conversion) of energy during an input/output cycle, and since we're dealing w/ a powerplant that doesn't produce all the rip-snorting power of the competition, it behooves us not to waste it on producing waste heat if we can avoid doing so.

 

Maybe the answer is the material they make (made?) superballs out of? That stuff seemed to get all the energy input back out again when I was a kid bouncing them in the driveway over the house to my friend on the other side. Put some o' that in your cush drive & smoke it!

[Guest ratchethack]

WRT hysteresis, I think we would ideally want something w/ less hysteresis ("H") than rubber [which is known for being a high H material, generally], since the greater the hysteresis, the greater the energy lost to heat from H during the cycle. And heat [along w/ oxidation, something a well-greased set of cush drive wedges will be somewhat protected therefrom] is what kills rubber's flexibility. Hence the interest in alternative materials like urethane compounds, which are generally known to be more heat & oxidation resistant than common neoprene-type rubbers [but I cannot comment on relative traits of H, since I don't know.]

I b'lieve you're unintentionally helping me make my point, Skeeve. As with shock damping, and tires and brakes for that matter, wot we WANT the material to achieve in a cush drive is a conversion of the damaging forms of kinetic energy into heat -- not to convert the smooth power delivery to the wheel into heat, but only the minute "spikes" on the curve, so to speak. If you can't convert and dump those unwanted forces in the form of heat, those forces will wreak havoc on the driveline components, as has been variously (and ever so numerously) described.

 

"Heat resistance" as an attribute or characteristic of a material, is NOT at all the same thing as the ability of a material to convert kinetic energy to heat via hysteresis!!!

 

Now this is just me, and this isn't a swipe at you or anyone else -- but having learned the hard way many many times myself, my take is best not meddle in areas where wot one doesn't know wot one doesn't know (got that?) can trip one up, big time. N'est-ce pas?

 

I would be very careful about making such blanket statements as "heat kills rubber's flexibility". Again, as I've pointed out many many times in this thread and the one prior, "rubber" is not a monolithic material like a pure element, in the same way that "metal" is not a monolithic material. Metal may be alloyed and treated in infinite ways to achieve very specific attributes, just as rubber can be mixed and engineered to exhibit a very wide range of specific attributes. In the case of cush drives, as in the case of tires, it's another a highly complex, highly engineered compound. I don't think you'd find a prohibitive loss of flexibility of tires under the extremely demanding, high heat conditions of road or track, for example. Contrary to your blanket statement above, racing tires, as well as many other kinds of tires and rubber-based compounds, are engineered to increase flexibilty with above ambient heat.

 

Please, may we have an experienced Materials Engineer chime in on this? There's just gotta be one or two hereabouts?? A tire engineer would be most welcome, since I reckon cush drive engineers might be as scarce as hen's teeth.

[Admin Jaap]

I just can't believe how much time and energy is spent (imo wasted) on the cush drive rubber's technical specs.

I think I'm going to ride tomorrow: 13 degrees and partly clouded. Springtime!!! And Sunday it will be even better

[Pierre]

I just can't believe how much time and energy is spent (imo wasted) on the cush drive rubber's technical specs.

I think I'm going to ride tomorrow: 13 degrees and partly clouded. Springtime!!! And Sunday it will be even better

Well, enjoy your ride Jaap. I do hope you don't hammer your drive line into submission before this cush thingie gets sorted.

[Admin Jaap]

I'm riding for 3 years w/o cush drive and all is well (knock on wood)

[Skeeve]

I would be very careful about making such blanket statements as "heat kills rubber's flexibility". Again, as I've pointed out many many times in this thread and the one prior, "rubber" is not a monolithic material like a pure element, in the same way that "metal" is not a monolithic material. Metal may be alloyed and treated in infinite ways to achieve very specific attributes, just as rubber can be mixed and engineered to exhibit a very wide range of specific attributes. In the case of cush drives, as in the case of tires, it's another a highly complex, highly engineered compound. I don't think you'd find a prohibitive loss of flexibility of tires under the extremely demanding, high heat conditions of road or track, for example. Contrary to your blanket statement above, racing tires, as well as many other kinds of tires and rubber-based compounds, are engineered to increase flexibilty with above ambient heat.

 

And after x amount of time exposed to the high heat levels of racing, the tires lose their flexibility ["traction"] & need to be replaced, regardless of how much rubber may [or may not] be remaining. Were you thinking something *besides* the heat they're exposed to affected the tires' traction?

 

Lest anyone think the hysteresis of the rubber has any special mojo, let us remember that other methods to relieve the shock loads on drivelines have been successfully used in the past, materials with [comparatively speaking] no hysteresis, like spring steel. In this instance, the easiest, lightest & least failure prone method was by sticking a bunch of rubber wedges into the drive hub. But their imperfect elasticity is not likely to be a particularly advantageous trait, only their ability to absorb the spike loads and redistribute them over time.

 

This entire thread is beyond academic for me, since I'm fully cognizant that there is unlikely to ever be a more cost-effective alternative to drilling the stock rubber pie pieces. But I'll be happy to go on observing, in the hopes that something offering superior performance [in terms of providing the "proper" level of cush w/o having to modify it] may arise from this turmoil.

[Ryland3210]

I disagree.

With no give of clutch, tire, or driveline, the finite inertia resisting the lifting of the front wheel limits the torque at the rear axle to the finite universe.

So in both the theoretical and real worlds, the torque will be finite.

And more relevantly, the lighter the front end and the higher the gravity, the less the torque will be at the rear wheel.

If you put a chromed steel front wheel on the front with disk rotors made of tungsten, you would get more torque than if you replace the front wheel with a nice carbon fiber wheel with ceramic rotors.

Infinite only occurs if there is absolutely no give. Inertia has a giving point that keeps the torque in the finite universe.

 

It's clear your education in the science of mechanics was incomplete, Dave. You haven't seemed to grasp the concept of a theoretical equation and how such a symbolic representation of physics can result in a result of infinity. I've done my best to provide a simplified version of the mathematics which are used to make these calculations and have failed in your case. I'm outta here!

[Guest ratchethack]

. . .I'll be happy to go on observing, in the hopes that something offering superior performance [in terms of providing the "proper" level of cush w/o having to modify it] may arise from this turmoil.

Well, Skeeve, my friend, according to this astounding thread, which even yet never fails to amaze and confound, you're clearly not alone in your hope. I'll keep observing this turmoil meself, out o' the inexplicable, probably perverse compulsion for watching the previously mentioned slo-mo train wreck.

 

There are very evidently those who seem to've invested a great deal of their aspirations for the future in such things as a "better" cush drive, not having identified any shortcomings wotsoever of the drilled stock one.

 

On my own lengthy personal list of hopes and dreams, I'm afraid this one don't make the list a-tall, since hopes and dreams of such things as warmer riding weather these days, and less mandatory freeway driving (I've got it down to less than a few miles a week now, all the rest on back roads) and um, oh yeah -- keeping my spice rack in order trump any and all hopes and dreams for my own cush drive wotsoever -- at least ever since I drilled it 3 years back.

 

But o' course, that's just me.

 

Now that you've mentioned it, I'm truly sincere in asking this question now. Can you either quantify or qualify wot "superior performance [in terms of providing the "proper" level of cush w/o having to modify it]" would mean to you, and explain how this would improve your life, and/or that of your Guzzi?

 

Enquiring minds. . . (well, you know)

[dlaing]

It's clear your education in the science of mechanics was incomplete, Dave. You haven't seemed to grasp the concept of a theoretical equation and how such a symbolic representation of physics can result in a result of infinity. I've done my best to provide a simplified version of the mathematics which are used to make these calculations and have failed in your case. I'm outta here!

No, it is clear that you have not grasped the flaw in your equation, obviously due to either your lack of education or brain cells.

[dlaing]

I'm riding for 3 years w/o cush drive and all is well (knock on wood)

No, actually it metal knocking on metal.

[dlaing]

You haven't seemed to grasp the concept of a theoretical equation and how such a symbolic representation of physics can result in a result of infinity. I've done my best to provide a simplified version of the mathematics which are used to make these calculations and have failed in your case. I'm outta here!

Since you are out of here you will won't read this, but maybe someone else can turn your theoretical equation into a real equation expressing your theory:

"To make the point with an extreme example, suppose the clutch and contact patch were replaced with rigid connections (infinite friction). If the engine is rev'd up and clutch dumped, the initial peak torque would be extremely high. If there was no elasticity in the driveline, it would theoretically be infinite but for a very short time."

You later qualified that no elasticity meant no cush.

I just don't get it.

If you dropped a feather on the upper end of a see-saw would you theoretically get a moment of infinite torque?

Does it become infinite if you take a hammer and hit the upper end of the see-saw such that it raises the other end?

If spy satellite debris traveling from above at many thousands of miles per hour hits the upper end of the see-saw is the force simply infinite torque for a longer period of time?

I just don't buy it unless someone can give a better explanation.

Here is a similar question:

"If a perfect sphere resting on a perfect surface makes contact at a single point, does its mass exert infinite pressure?"

-- Mawgan Asked Nov 19 2006 10:19AM

http://www.answerbag.com/q_view/90472

Here is my answer:

As the area approaches zero, the pressure would rise towards infinity. Assuming theoretical mathematics and not theoretical physics, the area of contact would be infinitesimally small and thus, assuming there was one iota of force, the pressure would be infinite. Because the area never reaches zero, the pressure must exist.

But that raises the question, would raising the force increase the already infinite pressure? If so, I believe we have a conundrum, and the answer may in fact be ultrafinitism. http://en.wikipedia.org/wiki/Ultrafinitism

But that is too heavy for me with my clearly incomplete education.

[dlaing]

Thanks Ratchet and Skeeve for the dialog on hysteresis.

I think the ideal level of hysteresis would be as little as possible without causing the bike to "pogo" fore and aft. (Please feel free to correct my untechnical terminology)

Greasing the cush will probably increase the pogo'ing, but since nobody has complained about it, I'll assume Skeeve is correct and we ideally should pursue less, not more hysteresis.

Thanks!

[Guest ratchethack]

. . .I'll assume Skeeve is correct and we ideally should pursue less, not more hysteresis.

Oh-oh. I reckon this means you'll be pulling your cush drive apart again to fill in the holes you drilled, Dave.

 

Since it'd be quite a chore to match the original rubber-based compound that was no doubt swept up off the floor after you drilled your blocks, and stuff the drill shavings back in (let alone get it to say stuffed in there), you could fill in the holes with something with less hysteresis than the rubber blocks themselves for a truly composite solution! Steel rods would be convenient to cut to shape and drive in. No hysteresis a-tall there. Wooden dowels would be easier to cut. Not much hysteresis there either. You could even pour a 2-part urethane compound of known lower hysteresis in the holes! Now this would seem to satisfy that burning, seething obsession you've had with urethane, and at the same time fulfill the seemingly still unfulfilled desire you've had to pursue "better", more "advanced" materials science on your cush drive for -- how long's it been now? A year? 2 years?

 

Please do keep us apprised.

 

"Better living" through Junk Science