iTopSpin

Current Posts => Collecting, Modding, Turning and Spin Science => Topic started by: ta0 on November 21, 2009, 09:20:02 PM

Title: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on November 21, 2009, 09:20:02 PM
I know Jeff has been waiting impatiently for months for me to post this. I finally took some measurements today.

The first graph compares my Throwback against the data I took on one of my Gates several years ago. Take into account that the initial speed of the Throwback on this particular throw is lower than the Gates. Time zero is when I land the boomerang so the graphs can be extended to find the initial speed.

The main conclusion is that the two tops are quite similar. There is not the big difference I found between the Gates and the Bearing King. If you want to split hairs, there is a little advantage (longer half-life) for (this) Gates with respect to (this) Throwback, so it will outspin it by a little.

(http://www.ta0.com/science/images/RPM_Throwback-Gates.gif)

The difference is more obvious on a logarithmic scale. The slope is proportional to the rate of spin loss and the Throwback is more steep.

(http://www.ta0.com/science/images/RPM_Throwback-Gates_log.gif)

Finally, some notes of caution. These are measurements on a single Throwback. It could be that  mine is not optimal (although it is the one I used to break the corkscrew world record.)  In fact, after I plotted that curve I decided I wanted one with the Throwback starting above 5000 RPM to match the Gates data. I had to throw a really hard boomerang and on a miss the tip of the Throwback came partially out. That may be the reason it performed a little worse after that, as you can see on this graph:

(http://www.ta0.com/science/images/RPM_Throwback-change.gif)

Hopefully, it is only dirty  . . .

Well, I know Yohans will not be happy about the YYJ top matching his top ::) To be fair, he had told me I should take out one of the two bearings of the Throwback and measure it like that. He told me it was probably a mistake to put two bearings and he believes with one bearing the spin time should improve. I think he is probably right. It will be an interesting comparison. Stay tuned.

Jorge

PS: Next time I will plot the data only every 10 seconds, not every 2 seconds  . . .   :-[
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: Pulp on November 22, 2009, 05:09:41 AM
Very interesting data.

The kids of my neighbourhood are interested in the spinning measurement.

Maybe next days I do something similar but with fix-tip tops. Spinning in hand and floor. And with the original tip and the tunned tips.
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on November 22, 2009, 11:08:24 PM
Pulp, are you just planning to measure spinning times or do you have a tachometer? These things can be pretty time consuming, you know . . . ::)

It is curious that while the loss coefficient slightly decreases with lower speeds for the Gates, the opposite is true for the Throwback. That there is not much difference a high speed makes me suspect that the different behavior at low speed is due to the bearings. Anyway, for normal (bearing top) playing speeds, above 2500 RPM, the tops behave remarkably similar. Half-life times in that range are between 90 to 110 seconds, about double the approximately 50 seconds I had obtained for a BK.
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: Pulp on November 23, 2009, 06:31:01 AM
I have a tachometer.

Yesterday I test the initial speed throwing of my kids (i haven't disk space in the video camera).

They throw between 4600-4200 rpm.

My best was 4880 rpm.

Soon the decay speed of "Cometa's" and "spaces" (fixed and bearig tips).
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on November 23, 2009, 01:14:18 PM
Are those "throw" speeds what you could first measure with the tachometer or did you extrapolate back to time zero? Even with very good bearing tops like the YYF and YYJ, the speed decreases appreciably in the first seconds.

It would be very interesting to test if the throw speed changes substantially with string length. Obviously, for any given top a higher initial spin rate will provide longer tricking time. I was very surprised when I found that I was getting 7000 RPM when throwing a Bearing King. Obtaining the initial speed only requires a few measurements with the tachometer to be able to extrapolate backwards. A camera is extremely useful because it can not only record the display but also the exact timing of the throw.

Nerd Warning
For the Gates and the Throwback the initial decay constant is about -0.008 1/s (i.e., time constant of 125 seconds or half-life of 87 seconds). The speed just after the throw will be

V = Vi exp (-0.008 t). 

were Vi is the initial speed. Therefore, the speed will decrease to 96% after 5 seconds or to 92% after 10 seconds.
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: poptop on November 24, 2009, 10:46:10 PM
Why do you think you can spin a BK so much faster?  Impressive, all of it.
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on November 24, 2009, 11:40:59 PM
Why do you think you can spin a BK so much faster?

I have no idea!
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: poptop on December 01, 2009, 10:57:57 PM
BK=Bionic Koma

Next we want to see the numbers for the trotolla STB--SpinTop Beast!
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on December 02, 2009, 12:20:15 AM
Well, I haven't got one yet. But probably soon . . .
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: kevinm on December 02, 2009, 11:23:32 AM
at the risk of drawing a second nerd warning, and possible
ejection from the game, may i ask how this translates in
the actual play of the top? are you going to road-test this further or is the spin the most telling characteristic of a top?
sorry for the newbie questions, but it's a rainy day at the
bike shop......
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on December 02, 2009, 02:17:57 PM
Well, it is just one measurement to consider but it is only relevant to bearing tops and in actual play other factors may be more important. I does give you a rough idea of how much time you have to do combos with a bearing top, that is the time until the spin gets to 2500 or 2000 RPM. However friction of the top body with the stirng and other factors will shorten this time in real play. If you were going to have just a spinner contest, then yes this would be the determining factor.

One of my projects for next year is to build a little setup to measure the moment of inertia of a top. Again, it will be just another number to compare tops but its influence on spintop performance is much more complicated than spinning times.

The ultimate measurement to take would be to put IC gyros or accelerometers in a top, (either with on-board logging or telemetry) and plot the spin rate while doing tricks . . . ::) One can dream!
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: Jeremy McCreary on July 15, 2016, 02:38:44 PM
Great data, ta0! I like your idea that the deviations from a constant decay rate at low speed relate to the bearings somehow.

I'd like to try this with my own tops and laser tachometer. How did you manage to get so many data points in a single spin?
Title: Re: Spin decay comparison of Throwback and Gates tops
Post by: ta0 on July 15, 2016, 03:01:12 PM
I'd like to try this with my own tops and laser tachometer. How did you manage to get so many data points in a single spin?

There is info on my setup here: Any RPM measurements? (http://www.ta0.com/forum/index.php/topic,153.msg875.html#msg875)

Perhaps I should merge the posts.