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Author Topic: Bicycle Spin Top  (Read 3348 times)

yoyospin

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Bicycle Spin Top
« on: March 11, 2017, 10:42:24 PM »

Jeremy asked for this...a spinoff :o of my bicycle themed fidget toys: CNC machined bicycle derailleur pulley, Cocobolo and Kingwood top with a variegated stone tip.
« Last Edit: March 11, 2017, 10:49:41 PM by yoyospin »
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jim in paris

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Re: Bicycle Spin Top
« Reply #1 on: March 12, 2017, 01:15:25 AM »

it's a beauty !thanx for showing ;)
the combination metal and wood works very well
does it increase the spin time a lot ?




jim
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Iacopo

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Re: Bicycle Spin Top
« Reply #2 on: March 12, 2017, 03:27:42 AM »

Good idea.  Also it is beautiful.  :)
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yoyospin

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Re: Bicycle Spin Top
« Reply #3 on: March 12, 2017, 12:43:48 PM »

it's a beauty !thanx for showing ;)
the combination metal and wood works very well
does it increase the spin time a lot ?

It does spin true, but no, the spin times are not that great. The aluminum disk, with all the cut-outs, make the derailleur pulley very light...not adding a lot of momentum. I could wrap a piece of bike chain around the disk, but it would probably destroy the balance. More experimentation is needed.
« Last Edit: March 12, 2017, 02:08:52 PM by yoyospin »
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Jeremy McCreary

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Re: Bicycle Spin Top
« Reply #4 on: March 12, 2017, 04:30:11 PM »

It does spin true, but no, the spin times are not that great. The aluminum disk, with all the cut-outs, make the derailleur pulley very light...not adding a lot of momentum. I could wrap a piece of bike chain around the disk, but it would probably destroy the balance. More experimentation is needed.

Beautiful piece, Ed!

Tops with perforated rotors like this one can produce wonderful visual effects, both at rest and at speed, and especially under pulsed lighting. The spoke-and-ring structure of your derailleur pulley falls into this category. In my mind, rotors consisting only of spokes also qualify. I'd expect this rotor of yours to generate spectacular patterns under a high-speed strobe and interesting video frame-rate effects to boot.

Most of the tops in the videos below have perforated rotors of one kind or another. (No need to watch either one past 2:00.)

https://www.youtube.com/watch?v=Un5d3CjroqE
https://www.youtube.com/watch?v=Bex1LsOt-pk

Unfortunately, some are lucky to stay up 15 sec with a hard twirl, and their rotor holes are largely to blame.

Rotor holes appear to reduce spin time in at least 3 different ways:

(i) Holes greatly increase the braking torque due to aerodynamic drag at all angular speeds, but especially right after release, when speeds are highest. This is a big deal because drag accounts for most of the deceleration during spin-down on a low-friction surface like a smooth counter.
 
(ii) Compared to a solid rotor of the same material, the absolute axial moment of inertia (AMI) lost to the holes reduces the top's ability to resist the total braking torque due to both drag and tip friction. (The bigger the hole, and especially the more peripheral the hole, the greater the loss of AMI.) The end result is a greater deceleration rate during spin-down at all speeds.

(iii) The associated loss of AMI per unit top mass increases the "critical speed" at which sleeping or steady precession becomes unstable and significant nutation sets in. (The top falls shortly thereafter.)

Each effect can cut deeply into spin time on its own. In combination, the loss of spin time can be quite severe.
« Last Edit: March 12, 2017, 07:57:20 PM by Jeremy McCreary »
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Jeremy McCreary

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Re: Bicycle Spin Top
« Reply #5 on: March 16, 2017, 06:21:58 PM »

Sorry, Ed. I managed to kill another perfectly good thread with LEGO and science.
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ta0

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Re: Bicycle Spin Top
« Reply #6 on: March 16, 2017, 11:46:28 PM »

That is in fact a very nice looking finger top. But I cannot stop wanting to spin it by wrapping a bicycle chain to the gear.  >:D

Jeremy: I finally watched the first of the two videos. That's a large variety of tops. But, yes, spinning times are disappointing (you may need a vacuum bell jar. :P ).
I found interesting the camera strobe effect on the elliptical top almost at the end. If you set the youtube video to run at 0.25 speed it will appear made out of jello.
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Jochen

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Re: Bicycle Spin Top
« Reply #7 on: March 20, 2017, 07:13:06 AM »

Wow... very nice! The wood and the anodized metal look awesome!

Jochen
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Jeremy McCreary

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Re: Bicycle Spin Top
« Reply #8 on: March 23, 2017, 12:41:27 PM »

Jeremy: I finally watched the first of the two videos. That's a large variety of tops. But, yes, spinning times are disappointing (you may need a vacuum bell jar. :P ).
I found interesting the camera strobe effect on the elliptical top almost at the end. If you set the youtube video to run at 0.25 speed it will appear made out of jello.

Thanks for pointing out the jello effect in the elliptical top (9:37) at 25% speed. Very cool, and an unexpected advantage of the elliptical shape. I keep forgetting that YouTube lets me adjust playback speed.

Some of the video effects I see here are pretty straightforward. Others are still puzzling -- including the speed-dependent spoke-bending effect best seen in the white propeller top at 4:20.
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Kirk

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Re: Bicycle Spin Top
« Reply #9 on: March 23, 2017, 08:42:18 PM »

yoyospin, What a lovely looking top!
Jeremy,  The blade bending effect is due to the type of shutter in the camera.  It is most easily explained by considering a common 35mm SLR camera.  The shutter has 2 curtains. One opens while the second one waits. After the set time the second curtain begins to close.  At high shutter speeds the shutter is never all the way open but only a moving sliver is open.  When photographing fast things like model rockets or race cars one can turn the camera over or on its side to make the rocket shorter or longer or make the fins show up warped.

Many cameras these days do not have a physical shutter.  Instead the image chip has an electronic shutter.  Often it will be what is called a "rolling shutter"  It acts much like a 2 curtain shutter (AKA focal plane shutter). That is to say only a sliver of the chip is exposed at once.  Since the top is spinning quickly compared to the shutter scan speed you get warped blades (I loved the jello effect) Turn the camera over to get the opposite warp.

Nerd alert. 
https://en.wikipedia.org/wiki/Rolling_shutter
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Jeremy McCreary

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Re: Bicycle Spin Top
« Reply #10 on: March 23, 2017, 09:55:08 PM »

Jeremy,  The blade bending effect is due to the type of shutter in the camera.  It is most easily explained by considering a common 35mm SLR camera.  The shutter has 2 curtains. One opens while the second one waits. After the set time the second curtain begins to close.  At high shutter speeds the shutter is never all the way open but only a moving sliver is open.  When photographing fast things like model rockets or race cars one can turn the camera over or on its side to make the rocket shorter or longer or make the fins show up warped.

Many cameras these days do not have a physical shutter.  Instead the image chip has an electronic shutter.  Often it will be what is called a "rolling shutter"  It acts much like a 2 curtain shutter (AKA focal plane shutter). That is to say only a sliver of the chip is exposed at once.  Since the top is spinning quickly compared to the shutter scan speed you get warped blades (I loved the jello effect) Turn the camera over to get the opposite warp.

Nerd alert. 
https://en.wikipedia.org/wiki/Rolling_shutter

Many thanks, Kirk. I was particularly puzzled by the non-rotational symmetry of the spoke-warping effect, but that makes perfect sense now, too.
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Jack

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Re: Bicycle Spin Top
« Reply #11 on: March 25, 2017, 09:54:57 PM »

« Last Edit: March 26, 2017, 11:39:08 AM by ta0 »
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