A Hub-Axle Treatment Evaluation Protocol

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dknowles67
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by dknowles67 » Wed Jan 21, 2004 10:15 am

The "lead" in a pencil is not "lead" at all but graphite (right?).
I found several years ago, that if I let my boys "color" the wheels where they contact the axles, and "color" on the axles with a No.2 pencil, the wheels spin longer than untreated wheels/axles. The graphite from a pencil lead seems to stick to the wheels/axles better than the powder does. Also, my boys are old enough, I trust them with a pencil now, and this seemed like a good way to get them involved. We spun the wheels w/o pencil graphite, and timed it. Then they went at it with the pencils, and we spun it again. They were able to see the difference it made.
I found that unpolished axles take the graphite better than highly polished axles, but I haven't been able to prove less polish + more graphite is better than more polish + less graphite.
Anyway, unless this is a totally rotten idea, I thought it might be another lubricant to add to the testing you were doing. I know the number of tests is already very long.



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Stan Pope
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Wed Jan 21, 2004 10:24 am

I should have thought to include pencil lead! Back when I was a kid (somewhre in the middle ages) I used a pencil sharpened at each end as ale for a small DC motor. Wouldn't provide much torque, but the graphite content of the lead helped the poor thing spin.

As a practical matter, I recall reading that pencil lead is a formulation of graphite and mud. I don't know how much of each, nor do I know what "grade of mud" is used. Or, perhaps, the mud doesn't stick.

Anybody know the details?


Stan
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Stan Pope
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Wed Jan 21, 2004 10:43 pm

Ah, yes! Not "mud"! "Clay!"

"Today's writing cores are a mixture of graphite and clay.
By varying the ratio of graphite to clay, pencil makers can adjust the "hardness" of the writing core. "


Stan
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by dmadman43 » Fri Jan 23, 2004 12:52 am

Stan Pope wrote:Ah, yes! Not "mud"! "Clay!"

"Today's writing cores are a mixture of graphite and clay.
By varying the ratio of graphite to clay, pencil makers can adjust the "hardness" of the writing core. "
would that suggest harder pencils had a lower or higher concentration of graphite? I'm unclear on what determines hardness (Now! Now! You all just stop right there!!!! :lol: )



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Stan Pope
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Fri Jan 23, 2004 12:58 am

dmadman43 wrote: would that suggest harder pencils had a lower or higher concentration of graphite? I'm unclear on what determines hardness
Quality pencils are graded by "hardness" and by "blackness". It is a reasonable guess that the "blackness" grade relates to graphite content. More likely that the "hardness" grade relates to the type of clay and the nature of processing of the lead.


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Re: A Hub-Axle Treatment Evaluation Protocol

Post by TurtlePowered » Fri Jan 23, 2004 10:20 am

dmadman43 wrote:
Stan Pope wrote:Ah, yes! Not "mud"! "Clay!"

"Today's writing cores are a mixture of graphite and clay.
By varying the ratio of graphite to clay, pencil makers can adjust the "hardness" of the writing core. "
would that suggest harder pencils had a lower or higher concentration of graphite? I'm unclear on what determines hardness (Now! Now! You all just stop right there!!!! :lol: )
From what I could tell, the lower number is more graphite to the clay mixture.



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Re: A Hub-Axle Treatment Evaluation Protocol

Post by OneTimeRunner » Fri Apr 02, 2010 10:36 pm

Stan,
I think your testing apparatus fails to account for centripetal acceleration. As the car travels through the curve of the track, the force on the axles is greater than the weight of the car. Sometimes as much as 3 or 4 times the weight of the car. The sharper the curve, the greater the force.

That means the weight on the wheels starts at 5, when it's at the starting gate, drops to less than 5 on the incline, increases to greater than 5 in the curve, and then goes back toward 5 on the flat, but doesn't reach 5 until the car stops again.

So, how would you adjust the test to make it more real? Maybe attach the apparatus to a singing pendulum that has the same radius as the curve of the track? :thinking:

It's still a good test. I'm just trying to help you "keep it real".



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Re: A Hub-Axle Treatment Evaluation Protocol

Post by FatSebastian » Fri Apr 02, 2010 11:06 pm

Wow OTR - way to revive an old topic! :thumbup: FYI the apparatus is now discussed here.
Form a "wheel" by fabricating a "ring" from wood. The OD is about 2".
I fabricated a couple of these disks according to the dimensions and they were not close to weighing 2 ounces. A donut ~3.5" in diameter cut from a piece of 1x4 would have seemed to yield about two ounces, based on my deductions, but I don't have a hole saw close to that size. My approach will now be to take a 7" wooden clock base (which is already round) and cut a hole in the center. I believe it will weight roughly 5 ounces when finished. My feeling is that this weight is reasonably close to what a woodcar wheel experiences, and the greater moment of inertia will keep the wheel spinning longer, possibly making the test less sensitive to timing errors. The purpose would be to test sporty's bore prep.

I would also like to try to put a pattern on the apparatus, then use a strobe to identify the time it takes for the apparatus to spin down to resonant frequencies with the strobe. Can't justify buying a strobe for that alone, at least not without trying it first. I looked online for software that might make my computer screen flash in regular fashion but haven't found anything I like yet. Perhaps video taping the spinning apparatus at a known frame rate might have the same effect?



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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Fri Apr 02, 2010 11:58 pm

OneTimeRunner wrote:Stan,
I think your testing apparatus fails to account for centripetal acceleration. As the car travels through the curve of the track, the force on the axles is greater than the weight of the car. Sometimes as much as 3 or 4 times the weight of the car. The sharper the curve, the greater the force.
Quite true.

The 2 ounces for the ring (use 'ironwood', FS!) was selected because the is a typical rear wheel load for one wheel. The 5 ounces you speak of is the total for 3 or 4 wheels. Seriously, the ring needs augmenting with some strategically placed lead slugs ... something that I have a lot of in my shop! My pencil apparently slipped when estimating volume and density. :(

The actual normal force (perpendicular force against track) at the starting line and early in descent is a fraction of g ... approx 0.865*g or what ever sqrt(3)/2 computes to vs. the 1/2 g force parallel to the track. Once on the flat, the normal force is constant 1g, except when bumps are encountered. The braking force from friction neither adds to nor subtracts from the weight. As my area of interest is the traditional Cub Scout track as described in the Cub Scout Leaders HOW TO Book, the G in the curvature is not nearly so exaggerated. The normal force gradually increases on that track from 0.865g to a bit over 1g during transit of the slope, settling back to 1g upon reaching the flat.

During design, I considered moving the eye screw above the ring rather than below the ring so that the force from the small weight would reduce the force between the wheel and the axle, but was not comfortable with the increased friction that the line would experience when making the 180 degree turn. But, I was really not interested in modeling a track. Rather I was interested in modeling lubricants under representative loads and speeds in a way that would be measureable by typically available instrumentation, e.g. a watch with a second hand.

By the way, when Randy Davis built his, he had a ring cut from steel for the purpose. I guess he had no handy supply of "ironwood." :)

On increasing the mass of the ring, I see no problem with altering the weight by a factor of 2 or, maybe, 3. The distortions of the parts should not be sufficient to hurt results. Increasing the diameter / rotational inertia does change the acceleration provided by the suggested 1/2 ounce weight (IIRC), so the duration of rotation may not be as long as you hope unless you also increase the starting weight!


Stan
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by FatSebastian » Sat Apr 03, 2010 12:06 am

Stan Pope wrote:By the way, when Randy Davis built his, he had a ring cut from steel for the purpose.
FWIW, Doc Jobe describes a similar apparatus in his Big Green Book made of metal. The book is not in front of me, but I recall he refers to it using a 3-letter acronym (the meaning of which I have yet to discover).



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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Sat Apr 03, 2010 12:19 am

FatSebastian wrote:
Stan Pope wrote:By the way, when Randy Davis built his, he had a ring cut from steel for the purpose.
FWIW, Doc Jobe describes a similar apparatus in his Big Green Book made of metal. The book is not in front of me, but I recall he refers to it using a 3-letter acronym (the meaning of which I have yet to discover).
The respective publication dates are interesting. :) As are the similarity of the weights selected. I looked at his biblio and conclude that we were developing at about the same time based on the same basic criteria. I didn't look at his in detail to see if he chose a similar acceleration method. I chose mine for consistency from run to run. His measurement hardware included stuff that I was only able to suggest in the end summary, since it was outside my casual capability and likely that of most of my readers.


Stan
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Jeff Piazza » Sat Apr 03, 2010 7:19 am

I tried building a weighted wood spin ring last year, described in tedious detail here, but wasn't happy with the results.

Recently I've been experimenting with this apparatus, based on an aluminum ring I made (I have a mini-lathe now, but didn't last year), and a laser tachometer I found here.
Image
Image

The idea is to alter the protocol to measure maximum spin rate, rather than how long the wheel spins, in part to make testing less susceptible to effects of wheel chatter.

I hope to develop some test data over the summer.

/JEP



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Re: A Hub-Axle Treatment Evaluation Protocol

Post by Stan Pope » Sat Apr 03, 2010 9:19 am

Nice variation, JEP! Well done!

Peak RPM should correlate exceptionally well to Cf! The accuracy of the tach reading is really important because, IIRC, the energy to angular velocity relationship obeys a square law, and the lubes are likely to be pretty close so that the energy difference (from friction losses during acceleration) will be compressed due to that square law effect.

In my mind, the ideal would be to measure the time for the first N revolutions (N is about 100 for a 28' track), because that time includes any "slow start up effects" and excludes what might be troublesome stopping motion at the end of the spin.

One of the considerations in the original work was to have an apparatus plan in which data could be exchanged and compared with minimal need to "recalibrate" based on whose ring and weight were used. In retrospect, the likely variations in the angular inertia of the various rings would prevent that from being realized.


Stan
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Re: A Hub-Axle Treatment Evaluation Protocol

Post by FatSebastian » Sat Apr 03, 2010 9:27 am

Great post, JEP! The laser tach is a great idea. How well does it workl? Also, does it work continuously like an analog tachometer? I would like to be able to measure, say, the decay rate of spin down. (For example, how much time does it take to go from X RPM to X/2 RPM?)

Has it been discussed anywhere why the outer diameter should be maintained at ~2"?



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