Interesting and odd

[Guest ratchethack]

I don't think the moment of inertia is the thing to focus on.

Dave, you've provided an excellent link that describes why moment of inertia IS the very thing to focus on. I spent enough years in College Physics to be one class away from a Minor in it by the time I graduated, and came to understand all of this very well, although I've probably forgotten most of what I once knew. Fortunately, as I've found is usually the case in the hard sciences, I still recall the core principles at work - in Newtonian Physics, they never change:

 

http://kosmoi.com/Science/Physics/Mechanics/tpecp2.shtml

 

If you scroll down to [2.4] MOMENT OF INERTIA IN DETAIL and [2.5] THIRD LAW OF MOTION / WORK & ENERGY, you'll see that there's no need to "guess" about any of this or wonder "if and perhaps". There's no guesswork or "maybe" or "perhaps" to be found here. It's all as solid and as absolute as anything in science gets... Again, Part III, if you don't have the moment of inertia of all the components measured as a starting point, no calculation of any kind will be of any use whatsoever in determining the effectiveness of counter-rotating brakes. From the link, the general definition of MOI is:

 

moment of inertia = SUM( mass * radius^2 )

 

in 2.5 at the link above, there's also an introduction of the "pennyfarthing" concept, whereby we consider moment of inertia of counter-rotating masses. There's also mention of coaxial configurations, examples of counter-rotating and self-cancelling torque and moment of inertia, and planetary gears - all of which apply to our consideration here.

[Steve G.]

This sort of stuff always reminds me of someone's description of the Vincent.

 

"A collection of solutions, hurtling down the road looking for a problem"

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Oh, but what a glorious looking problem a Vincent is!

Ciao, Steve G.

[Guest ratchethack]

Oh, but what a glorious looking problem a Vincent is!

Oh I most heartily agree. But have you ever given the front brakes on a Black Shadow a good look and considered the physics involved?!

[helicopterjim R.I.P.]

Oh I most heartily agree.  But have you ever given the front brakes on a Black Shadow a good look and considered the physics involved?!  

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British physics conforms to the rules of another universe.

[Guest ratchethack]

British physics conforms to the rules of another universe.

Heh, heh.....I reckon it's the same universe where what "could happen" and "should happen" trumps what DOES happen...

 

Well, these brakes could stop it and should stop it...

[dlaing]

If you scroll down to [2.4] MOMENT OF INERTIA IN DETAIL and [2.5] THIRD LAW OF MOTION / WORK & ENERGY, you'll see that there's no need to "guess" about any of this or wonder "if and perhaps".  There's no guesswork or "maybe" or "perhaps" to be found here

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No, we still have to guess at the measurements, unless you are willing to measure, we'll still be guessing.

If you had recalled your physics a little better you could have explained, that the first set of calculations that I presented was wrong because I assumed a linear progression of the force in question as the mass moves away from the center.

In fact it appears that if the force in question is the torque, not the force as defined in my last post.

The torque, like the MOI, simply increases exponentially as the mass is moved further from the center.

The torque, unlike the MOI also increases linearly as the RPMs increase

The moment of inertia is not the end result, but it is the first thing to calculate.

Measuring the masses and radiuses to determine the MOI is not trivial, unless one simply guesses.

I kind of doubt the makers of this braking system took accurate measurements, but rather guessed, and probably guessed wrong and optimistically.

If someone knows the exact weight of a tire, a wheel and a brake rotor, let me know, and will do another rough estimate. I was getting the numbers from tire shipping weight and boasts of how much lighter wheels and brakes are...if the progression was linear this would have been accurate enough to see if they were close or need a boat anchor to counter the force.

Learning that the torque increases exponenentially has given me a new disrespect for perimeter brakes. What are Buell and G&B thinking?!?

[Guest ratchethack]

If you had recalled your physics a little better you could have explained, that the first set of calculations that I presented was wrong because I assumed a linear progression of the force in question as the mass moves away from the center.

Uh, gosh Dave, should I apologize then for not providing a detailed critique of y'er calculations? Frankly, I hadn't even looked at 'em beyond y'er drive off the tee, 'cause (as mentioned in different ways repeatedly before) I could see you were pretty far off the fairway - deep in the tall grass... D'you play golf? Sorry, but my recollection of the principles of Physics is quite good enough to notice that you weren't even using appropriate values, for starters... I thought my use of the term, "pointless" covered y'er math here pretty well, making it hardly worth further consideration.... HINT- using the square of the radial dimension in your calculations instead of a linear progression wouldn't have got you any closer to the green....

The moment of inertia is not the end result, but it is the first thing to calculate.

Is there an echo in here? I already said that many times (see Parts I - III above).

 

OTOH, you'd previously said:

I don't think the moment of inertia is the thing to focus on.

I kind of doubt the makers of this braking system took accurate measurements, but rather guessed, and probably guessed wrong and optimistically.

But who would've imagined?

If someone knows the exact weight of a tire, a wheel and a brake rotor, let me know, and will do another rough estimate.

Again, Part IV, (yep, there IS an echo in here!) if you don't have the moment of inertia of all the components measured as a starting point, no calculation of any kind will be of any use whatsoever in determining the effectiveness of counter-rotating brakes. You cannot accurately calculate the MOI from the weight and diameter of any of the components, with the possible exception of the disks themsleves, and then you'd have to find an accurate way to back out the "missing" mass of the ventillating holes... In any case, estimating won't provide significant enough numbers to be of help in evaluating overall effectiveness...remember - any inaccuracy on the counter-rotation side of the equation carries with it a ~5/2 multiplier....

 

Dave, this is getting tiresome. If y'er attempting to show hard mathematical and physical proof of what the goofuses who applied for the patent and put up the Web site more'n likely never understood themselves, I reckon y'er tilting at windmills... best let 'er go, my friend!

 

Don Quixote and Sancho Panza gave it their very best shot. What'd it get 'em?

 

NOTE: In the illustration below, Don Q is flat on his butt, his lance broken in twain. Looks like Sancho got Don Q's boot right square in his Castilian family jewels. And yet the windmill appears entirely serviceable...

[dlaing]

Uh, gosh Dave, should I apologize then for not providing a detailed critique of y'er calculations?    

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Clearly you made little effort to comprehend what I was writing....typically you, no need to apologize.

HINT- using the square of the radial dimension in your calculations instead of a linear progression wouldn't have got you any closer to the green....

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See, you are missing my point completely.

Using the linear progression got me, or rather the inventor, right up to the cup.

When using the square, the impact of the tires dimension becomes more challenging to compensate for, and your analogy of boat anchor weight almost becomes accurate.

You cannot accurately calculate the MOI from the weight and diameter of any of the components.  Estimating won't provide significant enough numbers to be of help in evaluating effectiveness...remember - any inaccuracy carries with it a ~5/2 multiplier.... <_ src="%7B___base_url___%7D/uploads/emoticons/default_sad.png" alt=":(">

85791[/snapback]

I disagree.

Dave, this is getting tiresome. 

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It did not have to be....sorry you could not learn from the discussion as I did.

Some how or other you were responsible for me learning a law of physics...thanks <_>

[Guest ratchethack]

Some how or other you were responsible for me learning a law of physics...thanks   

*sigh*......do you actually mean to say that I can say, "Mission Accomplished"....??

sorry you could not learn from the discussion as I did.

Now, are you being sincere, Dave? If there's been any "learning" that I seem to've missed, by all means - could you point it out?

 

No, never mind. I think we've been done here for quite awhile.

 

Always an uncommonly great pleasure, Dave.

[dlaing]

Don't know about the technology, but that website layout sais "don't take this seriously..."

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I looked for that but could not find it....oh well.

In any case this adventure has got me enthused to save weight on the front wheel.

before I had no idea that you could buy ceramic rotors that are one third the weight.

A few pounds off the wheel would not be a bad idea either.

Ceramic bearings could also save a couple ounces, but won't help much in the rotational department.

All of this would be expensive

carbon fiber wheel $2000 maybe less

ceramic rotors $1800 MSRP

ceramic bearings $200 maybe less

Yes they appear to have fudged their numbers, and the 3# and 5# targets may be unobtainable without adding lead weight or making the rotors out of tungsten, but if this reverse rotating rotor got slightly better results than a $4000 20# wheel assembly and cost only $2000, it might be worth it.