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Author Topic: Any RPM measurements?  (Read 4273 times)

jim in paris

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Any RPM measurements?
« on: September 05, 2009, 03:41:52 AM »

salut les gars de l'ohio !

and welcome !
here it's a small log cabin where we have plenty of room for spintop heads
about the physics of spinning objects , i'm sure you're aware of Spintastics school programs , started long ago by dale and valerie oliver
here is the link to one of their science programs
http://www.spintastics.com/SSTDocuments/YoCurriculumSCIENCE%20pdf.pdf
we often come across physics questions and discussions....(...°)
have you ever measured the speed of your tops , the max duration of spin and the decay time ?
......great pictures with the thumb up !
thanx

good day

jim
« Last Edit: October 23, 2009, 10:52:04 PM by ta0 »
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johnm

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Any RPM measurements?
« Reply #1 on: September 05, 2009, 08:30:18 AM »

have you ever measured the speed of your tops , the max duration of spin and the decay time ?
jim
Surprisingly, our department does not have a non-contact tachometer and we've never measured a lifetime.  I'm not sure exactly what the defined 'standard' for duration would be since everyone throws differently and the start/endpoints are a little arbitrary.  However, with some chosen definition of start and stop points, the MAXIMUM duration for some tops could be measured soon as we will have a professional thrower on site ready for action. :) :) :) 

I'm sure we could buy a tach. since I've had a passing thought of developing an experiment for our advanced physics lab where the end measurement would be the kinetic energy transferred from one top to the other in ta0's spintop motor. (have I mentioned how clever that is?)  However, the 'to do' book is already too heavy to carry and developing a laboratory exercise that clearly assists with physics understanding is very time consuming.
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hemingsoft

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Any RPM measurements?
« Reply #2 on: September 05, 2009, 08:36:34 AM »


have you ever measured the speed of your tops , the max duration of spin and the decay time ?

jim

John,

I thought we did measure the the speed of one of the small early wooden peg tops.  Or have re disregarded that as inaccurate?
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ta0

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Any RPM measurements?
« Reply #3 on: September 05, 2009, 09:47:37 AM »

With Jeff we have done measurements of rotational speed of a few tops and we came up with a nice way of obtaining the RPM curve as a function of time (where is topspinnig.com when you need it?). We even calculated the decay constant or half-life! It is a little tedious to do, so perhaps you could get some of the undergrad students to do it for other tops ;D Actually, I promised Jeff I would do it for the Throwback . . . Mmm, I'll let him start a new thread about this . . .

I imagine you can take the handle out of the demo top, put a tip and play with the university-issued toy  :D
« Last Edit: September 05, 2009, 10:25:48 AM by ta0 »
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SpinQueen

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Any RPM measurements?
« Reply #4 on: September 05, 2009, 01:53:15 PM »

Is this the chart you were looking for?

http://www.topspinning.com/toptalk/viewpost.php?post=5794
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johnm

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Any RPM measurements?
« Reply #5 on: September 05, 2009, 09:06:24 PM »

I thought we did measure the the speed of one of the small early wooden peg tops.  Or have re disregarded that as inaccurate?

Yes, Ken the maintenance man had borrowed a tach to tune an air handler so we did a single measurement on a spinner on the floor-- about 5000 rpm I think shortly after landing and lining up.

I didn't mention it because it wasn't timed and I think the interest is for spin times on the bearing tops.  Since they (the two way bearing kind) can't be regenerated, the decay time is important for trick count in contests and for Jim, knowing the decay time may help with planing transition during a show.

I had seen and like the data ta0 and Jeff have discussed (thanks for the link SpinQueen).  If we proceed with a real lab experiment, I would look for a USB tach to assist with data collection.  Its nice to have other people's money to spend--thanks taxpayers.
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jeffs

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Any RPM measurements?
« Reply #6 on: September 05, 2009, 10:45:36 PM »

The thing Jorge and I were attempting was to find a way to compare two tops without having to take into account how hard they are thrown, exactly the problem raised a couple of posts back by johnm. The idea was that if resistive forces in a top go linearly with RPM, then RPM vs. time would be a decaying exponential. If this were so, then the spin time for a given top would have an inherent half-life which could be used as an objective measure of how good the top is. I could say, "My Acrobat has a half-life of 93 seconds. How about your Jon Gates?," and the answer you give based on your measurements would give a direct comparison of our tops even though you spin a top twice as fast as I do. A side benefit of the fitted exponential curve is that it could be easily extrapolated back to time zero to determine the RPM at launch, an interesting number which is not easy to measure directly.

Well, the curves made, in Jorge's case, by taking a video of the the tach while the top is spinning and using the time base on the camera, are beautifully coherent things that sure look like an artist's conception of a decaying exponential, and when you do a semi-log plot, they turn into almost perfect straight lines. Almost. The computed half-lives for a given top are still somewhat sensitive to initial RPM, hardly a surprise given the highly idealized nature of the underlying mathematical model. It may be more of a surprise, however, to see how stable they actually are over a wide range of starting velocities. The case can be made that a measured half-life (pseudo half-life ?) of a top says a lot about how it's going to play. And it is information that we can confidently exchange.

A neat feature of the model is that you only need to measure the RPM at two different times in order to compute both the half-life and the initial RPM. In practice one would use more measurements and perform some kind of best fit, of course, but there is no need to be intimidated by the vast reams of data that Jorge and I produced in our early efforts to come to grips with this thing.

I assume that ta0 will jump in here to correct any errors or false emphasis that I have introduced into this very brief synopsis of a lot of time that we ran down the drain collecting and poking around these data.
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Jeff Smith, Kalamazoo, MI

ta0

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Any RPM measurements?
« Reply #7 on: September 05, 2009, 11:37:07 PM »

Nice to see you posting Jeff! If we could now just smoke out daveid  8)

A USB tach would have been wonderful! We would had plotted every top.

My dream is a top with accelerometers and telemetry!  :P
« Last Edit: September 06, 2009, 08:52:43 AM by ta0 »
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ta0

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Any RPM measurements?
« Reply #8 on: September 06, 2009, 09:28:32 AM »

This is my setup for taking the measurements of RPM decay using a laser tachometer (with no digital output) and a camera recording the measurement.


Not only the data is recorded against the video time base, but also the instant of the boomerang to establish time zero. The original post of the setup is here. Actually, Jeff started it here.

This was the main result (thread):


Measurements on a Gates top seemed to show that a little tape can affect the results due to air friction (I am still surprised about this):


Or on a logarithmic plot to show them as lines (the slopes give the decay constants):


Also took measurements for a Takeshi BK mod:


The decay constant varies just a bit between the initial high rotation regime and lower speeds, but seems to be a useful characteristic to compare bearing tops. For example, the half-life of the Gates is more than double that of the BK.



« Last Edit: September 06, 2009, 10:07:29 AM by ta0 »
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agentsac

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Re: Any RPM measurements?
« Reply #9 on: September 06, 2009, 12:28:14 PM »

the tape has an amazing effect on the gates. i wonder if the winding groove and rough finish on the bottom of the BK create enough drag to affect spin times. i'm sure that there are other factors that make the gates spin longer, but i think it is important to note that sometimes little things can have a big impact on performance. take note all you spintop manufacturers!
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johnm

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Re: Any RPM measurements?
« Reply #10 on: September 06, 2009, 10:49:01 PM »

Thanks Jeff for the details. 

Wow! that's a lot of data to pick off a video by hand and a lot of self control to hold the tops that long and resist doing a trick.

I wonder if Alan or Eric has cleaned up a BK like the polished QS.
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Eric

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Re: Any RPM measurements?
« Reply #11 on: September 07, 2009, 03:24:25 PM »

While I haven't done it yet, I think that Alan has cleaned up and polished a BK, a clear one at that.

Here's a bit to add to the RPM and spin decay discussion.  In early 2005 when I was in California for one of John Rollins' famous "Yo-Downs", Don Watson (colaborator and friend of Tom Kuhn's for those of you who don't know Don) and I did some simple rpm tests on one of my big bearing tops.  This top (8 inch diameter):



Those of you who know Don won't be surprised that he had a battery operated tachometer in his car.  We used the tach on the top over 5 throws (after which I was too tierd to hold a 4 pound top on my hand any more....).  While we didn't film it, or generate any other data, I vividly remember the best throw.  At the beginning of the throw, right after I had caught the top in my hand and had stabilized it, Don got a reading of just under 4000 rpm (3950 I believe).  5 minutes later, it was at around 1150 rpm......it spun for about 1 1/2 minutes more with me fighting to keep vertical for the last 30 seconds or so.  The bearings in the top were relatively new and very clean high-end skateboard bearings (Bones Swiss for you skateboarders), which leads me to believe that in measuring rpm and spin decay on bearing tops that some factoring in of the size and type of bearing may be important.

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