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[Jeremy McCreary]

How many runs each, with and without fairings?

[Iacopo]

Fairings are not good for JBB

Thank you for trying. 
It is interesting to see that you have clearly more air drag with the fairings than with the naked spokes, I didn't expect it.

[ortwin]

How many runs each, with and without fairings?

Only one of each for this test.

[Jeremy McCreary]

You're happy with so few data points?

[ortwin]

You're happy with so few data points?

As they say around here:

"Happiness runs in a circular motion!!!"
But yes, I think I am fine with that for now.
The wrong reason for this is that I expected it due to my former fairing experiments.
Another reason is, that to me it makes sense: Large area of fairing surface makes lots of friction. The surface goes with the square of the radius.
On the other hand spokes create drag. But the spokes length (surface) goes only linear with the radius of the flywheel. So the spokes will eventually win.Surely a over simplification, but not counterintuitive.

[ortwin]

Alright, here come some more data points: JBB spinning for 24:17
Full spin video plus spin decay curve as recorded with that new tachometer I received yesterday. 






This is a graph of the raw date minus quite a few values that where high above the curve. I set those to zero by hand.Not all values are lying on the curve. Mostly this is due to precession and to the traveling of the top, the laser did not always hit it properly. Especially in the later phase of the spin this becomes a problem. So this is another reason why precession in the beginning is not good.I am not happy with the data handling program I am using. That is why I did not put much effort in preparing a better graph. I have Libre Calc. Similar to Excel which I also do not like much for this kind of task. I need to get something similar to "Origin" again.I put the date in an attachment for the hardcore fans.


Another Q&D production - Although as spin times become longer and longer you almost can't call it quick any longer.

[the Earl of Whirl]

[ortwin]

Yes, I copied that line into my post directly from the signature  of "the Earl of Whirl" without asking, so you have every right to throw this video at me. For me that woman is a bit scary, sorry, I liked the video that flew around here a few weeks ago with the original performer (Donavan?) a lot better.

[Jeremy McCreary]

You're happy with so few data points?

Another reason is, that to me it makes sense....

Science is a way of trying not to fool yourself.
  — Richard Feynman

Sometimes fairings reduce overall braking torque, sometimes they don't. How to predict for a given flywheel on spokes? Who knows?  Not me.

[Jeremy McCreary]

Alright, here come some more data points: JBB spinning for 24:17.... This is a graph of the raw date minus quite a few values that where high above the curve. I set those to zero by hand.... I am not happy with the data handling program I am using. That is why I did not put much effort in preparing a better graph. I have Libre Calc. Similar to Excel which I also do not like much for this kind of task. I need to get something similar to "Origin" again.

Excel works well for me, but I've been using it for decades. Most of all, I want (1) easy mathematical analysis, (2) easy plotting of the raw SDCs, and (3) easy addition of exponential trendlines. Why the last? Because I find the exponential best fit useful as a measurable reference curve providing an easy way to compare our empirical SDCs. The exponential lifetime (reciprocal of the trendline's decay constant) is a very handy figure of merit for decay rate prior to the SDC tail.

Excel does plotting and exponential trendlines well enough, and with pain I'm willing to live with. Just got Google Sheets to do all 3 things, too, but much more painful and much less flexible.

Not all values are lying on the curve. Mostly this is due to precession and to the traveling of the top, the laser did not always hit it properly. Especially in the later phase of the spin this becomes a problem. So this is another reason why precession in the beginning is not good.

I also had to hand-cull some obvious outliers due to precession and travel. And I can relate to the trouble you had twirling JBB straight into quiet sleep. I get around that with a starter. If I'm just capturing an SDC, why not?

In my experience, the larger the AMI, the smaller scrape angle, the shorter the stem, the larger the tip radius of curvature, or the more concave the support surface, the more tries it takes. It's also important to hold your mouth just right during the twirl.

[ortwin]

.... I get around that with a starter. If I'm just capturing an SDC, why not?
...

Why not? Because you waste a chance for practicing your hand start abilities!
Alright, I might use the ribbon method with two strings if you want a better SDC.
 

...
Excel does plotting and exponential trendlines well enough, and with pain I'm willing to live with. Just got Google Sheets to do all 3 things, too, but much more painful and much less flexible.

...

For this kind of thing Excel is giving me personally too much pain. I used to be used to "Origin" because I used it a lot. I am trying to look into similar freeware at the moment.

...

In my experience, the larger the AMI, the smaller scrape angle, the shorter the stem, the larger the tip radius of curvature, or the more concave the support surface, the more tries it takes. It's also important to hold your mouth just right during the twirl.

Yes, but I try to see that as a good thing. You can look at it as positive play value, it keeps you busy like adjusting all those screws and things to get it balanced. If you would have bought a ready made top for cheap, and you would be able to spin it for half an hour with a single twirl almost effortless and without adjusting or lubing anything, you would be bored by it after a few days, not?

[ortwin]

JBB 26:22
The improvement here came mainly from the fact that I took the balancing weights off the spokes and luckily I could balance it well enough by tensioning the spokes. 
That there is less air drag now is best seen at the higher speed end.
The contact point is also a bit closer to the center of mass. It extends now only about 1 mm below  the ring, before that was about 2 mm.  I think that was a little advantage bringing the topple speed down to 82 RPM from 85 RPM.
The starting speed might have been a bit higher ~730 instead of ~720 RPM but that does not make a big difference.


 

Sometimes it is easier to record the data for the spin down curve by hand still:

RPM	t
~730	00:00
650
600	01:42
550
500	03:20
400	05:35
300	08:51
200	14:06
190	14:48
180	15:34
170	16:21
160	17:12
150	18:07
140	19:05
130	20:08
120	21:15
110	22:27
100	23:46
90	25:09
82	26:22

[Jeremy McCreary]

Why not? Because you waste a chance for practicing your hand start abilities! Alright, I might use the ribbon method with two strings if you want a better SDC.

You could get in 20+ practice starts in the time it takes to do one JBB time trial. And with the benefit of instant feedback from the top's behavior and a single speed measurement.

I recommend an inline starter that effectively extends the stem during spin-up. That allows the clean release and tilt control needed to avoid unwanted precession and travel.

If you would have bought a ready made top for cheap, and you would be able to spin it for half an hour with a single twirl almost effortless and without adjusting or lubing anything, you would be bored by it after a few days, not?

Couldn't agree more. The chase is usually most of the fun. The main exception in my case: A pesky wobble that drives me nuts.

[ortwin]

JBB hardware update
Today the mailman brought me some new modules for Junior Brass Band directly from the lathe.



 A : three axes of different lengths with tips from ball point pens. The balls have a diameter of 0.5 mm and are made of tungsten carbide
B : knurled knobs for better twirls
C : counter nuts, spacer

 An assembled the new version of JBB looks like this:


still spinning

For looks it is an improvement, performance-wise I can't say anything yet, but it feels good! Of course I hope for improvement in spin time.
Maybe by one minute caused by the smaller tip diameter and another minute caused by higher starting speed due to a better knob?
Only wild guesses fueled by hope.

[Jeremy McCreary]

A handsome and capable piece of gyroscopic equipment you have there, Mr. Ortwin.

What is the diameter of the knurled knob?