iTopSpin
Current Posts => Collecting, Modding, Turning and Spin Science => Topic started by: jim in paris on September 14, 2023, 02:28:52 AM
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for his 1st festival des toupies in Brittany
mathieu is building a big chinese top
all details in this article in French
https://actu.fr/bretagne/bourbriac_22013/en-bretagne-ils-fabriquent-la-plus-grande-toupie-de-france-lourde-de-200-kg_60032861.html
the centering of the tip will be the last step in the process, before the whipping during the festival
good luck!
jim
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Wow! Impressive!
Here are a couple of photos from the festival Facebook page:
(https://i.ibb.co/grVCMBw/369776658-194453326976406-3245027708354383926-n.jpg)
(https://i.ibb.co/02GRNGJ/374953738-201712676250471-560322732613998716-n.jpg)
I'm very happy that Mathieu has been able to accomplish his dream of organizing a spintop festival (https://www.ta0.com/forum/index.php/topic,7019.msg77316.html#msg77316) in Britanny. And with the giant whip top he even managed to upend the other fests in Europe. I wish I could be there (but it coincides with the Zapopan festival).
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That's a cool set up with the power planer on a track to true the Big Top. Can hardly wait to see it in action!
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https://www.ouest-france.fr/bretagne/bourbriac-22390/video-pres-de-guingamp-le-festival-de-la-toupie-seduit-petits-et-grands-599ce9c1-0ae7-379b-9fae-d1d04765a32f
the big top spinning
bravo !
jim
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The top was spun by the whipping but unfortunately not enough to spin freely, so it was always hanging from the support. It's going to be a challenge to make it spin freely, but if he brings it to Marines or Loon Plage festivals, I think we can achieve it. In China quite bigger tops are spun that way, although this one is more skinny what might make it more difficult.
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Here is a unique method for starting big tops before whipping.
https://i.imgur.com/o19gv0p.mp4 (https://i.imgur.com/o19gv0p.mp4)
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Ha! Love it! But the way I would like to start it is by running away with a rope, perhaps two people in opposite directions.
Great to see you posting, Alan. Your name was mentioned several times this weekend at the Mexican nats. As always, Figaro was a star and many people asked who made it.
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In the video, the maker (Mathieu) claims that his top has a mass M of "1,2 tonnes" or 1200 kg. Problem is, a wooden top can't be anywhere near that dense.
Using the video with a ruler against the screen, I estimated the top's dimensions by scaling them against Mathieu's height, which looks average for the crowd. An average French male is 1.75 m tall per Wikipedia.
The wood looks like pine, which has an ovendry specific gravity (SG) of about 0.4. But If the claimed M = 1200 kg is correct, my estimated dimensions imply an SG of 7.0 —roughly that of iron. To come in at pine SG, the top would need a mass of ~70 kg — roughly that of an average human.
Regarding spin-up methods
Luckily, a uniform top's critical speed against gravity depends only on size and shape, not mass or density or SG. Using my estimated dimensions, this top has to spin faster than ~430 RPM to stay up on its own.
Attainable by whipping alone? By motor scooter? By human-powered rope-pulls?
Online spreadsheet
You can check my estimates and calculations here:
https://docs.google.com/spreadsheets/d/1k4blVudPHOg0nPTooYPhLWpLUfj-nL_6uJ3TKdFWDvM/edit?usp=drivesdk
Feel free to play with the numbers. Your changes affect only a local copy of the sheet, not the master in the cloud.
Please let me know if you find errors or think my estimated dimensions are way off.
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The top that Mathieu built weighs 200kg.
On the video he mentions a Chinese whip top that weighs 1,200 kg.
The record I'm aware of is actually 1,306 kilograms (https://www.ta0.com/forum/index.php/topic,3564.msg36460.html#msg36460).
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The top that Mathieu built weighs 200kg.
On the video he mentions a Chinese whip top that weighs 1,200 kg.
The record I'm aware of is actually 1,306 kilograms (https://www.ta0.com/forum/index.php/topic,3564.msg36460.html#msg36460).
Well, so much for my French. Still, if my estimated top dimensions are in the ballpark, the SG is still well above that of pine and other softwoods at 200 kg total mass. (See closeup photo of top. Doesn't look like hardwood grain to me.)
Could Mathieu be much taller than average? Could the top have a steel core — more than just a central rod or bolt?
Addendum: Went back and re-estimated dimensions, then updated online spreadsheet. At 200 kg total mass, I now estimate an SG of around 1.0 and a critical speed of around 362 RPM.
Oak — the densest common wood — has an ovendry SG of around 0 7.
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I did a similar calculation (https://www.ta0.com/forum/index.php/topic,3564.msg36475.html#msg36475) (great minds think alike ;) ) for the 1,306 kg top and I also came out short. I wonder if big whip top makers are like fishermen . . . ;D
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I love fallowing the math around this whip top. I've yet to measure the rpm's of my Big Tops. Once I know the rpm, I'd like to know the surface speed and if there is measure of energy . We have plans to use one of the rental electric scooters available in NYC to power a top, but also a whip which I need to make. Can you offer suggestion of specific material and size as a guess to get me started for a whip? Thanks!
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I love fallowing the math around this whip top. I've yet to measure the rpm's of my Big Tops. Once I know the rpm, I'd like to know the surface speed and if there is measure of energy .
We'd love to see your top and spin-up process! To get the rotational kinetic energy and critical speed (the minimum needed to stand against gravity), we need estimates of the top's moments of inertia and the distance from its tip (ground contact) to its center of mass (CM). And for those estimates, we need its mass, size, and shape.
For now, I'll assume a uniform cylindrical top of mass M, radius R, and length L with a CM-contact distance H > L.
For these calculations, best to work in meters, kilograms, and seconds and in angular speeds in radians/second (rad/s) rather than RPM. If N is the rotational frequency in RPM and w is the angular speed, then
w = pi N /30 (in rad/s)
A mark on the side of the top then travels at surface speed
V = R w (in m/s)
This top has an axial moment of inertia (AMI) of
I3 = ½ M R² (in kg m²)
and a rotational kinetic energy of
E = ½ I3 w² (in Joules)
The transverse moment of inertia (TMI) about the contact is
I1 = M (3 R² + L²) / 12 + M H² (in kg m²)
The critical speed needed to stay up is then
wc = sqrt(4 I1 M g H) / I3 (in rad/s)
where g is the acceleration of gravity in m/s². This means a critical surface speed of
Vc = I3 wc (in m/s)
To keep the top up by whipping alone, you'll need a whip and whipper capable of hitting the top at speeds well above Vc with good traction on the top.
Given the human factors involved, whip design has to be full of tricky trade-offs. Other members can better advise you on that score, but I'd see what you can glean from videos of successful whips for tops about the same size as yours.
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Wow, thanks for the homework! I may need some help with the calculations. My Big Top, Dorothy Dot, measures 95cm tall x 72cm max diameter, 30kg. Hand carved (hollow) on a lathe, inside and out. Spin times starting with an impact gun indoors average 6 - 8 minutes. Reconnecting the impact gun mid spin to extend the time is usually possible provided the top isn't wobbling too much. However, it would be nice to have human power take over. I imagine traction of the whip will be key so an average rope might not be ideal. If there is a rubberized material or similar traction type material that anyone can recommend, that would help. I can scale images of other whips from videos to get dimensions and play with what works/fails. Attached is an edited video that does not show the whole spin time, video by Mark Hayward Aug. 2023. Miamisburg, OH. That's me operating the impact gun. https://youtube.com/shorts/UrTRya643zc
The next Big Top (#8) is in planning and hope to have it built over winter.
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Wow, thanks for the homework! I may need some help with the calculations. My Big Top, Dorothy Dot, measures 95cm tall x 72cm max diameter, 30kg. Hand carved (hollow) on a lathe, inside and out. Spin times starting with an impact gun indoors average 6 - 8 minutes.
What a beauty! Impressive spin time, too.
The first surface speed formula I gave still applies, but there are no easy formulas for the moments of inertia of a simple solid peg top, let alone a hollow one. And you need at least the axial moment for the energy estimate you're after.
However, there are formulas for the moments of a roughly similar shape — the solid spherical cone (https://mathworld.wolfram.com/SphericalCone.html). And there are ways to subtract out the moments of the wood lost to hollowing if the finished top's walls are of roughly uniform thickness.
With the following info, I'd be happy to tackle that in a Google sheet you could play with online. (You know you're a hopeless nerd when you enjoy challenges like this.)
Q1. What kind of wood? Same throughout?
Q2. Any steel inside? If so, what size and shape, and where? Weights of the steel parts if you have them?
Q3. What's the dominant wall thickness? Any big departures? Where?
Q4. What's the distance from the contact to the max diameter, taken along the spin axis?
Q5. Long shot: Do you happen to know the distance from the contact to the top's CM, taken along the spin axis?
A rough cutaway sketch of the void and steel with some dimensions would be a big help.
No worries if all this is more work than you bargained for. You could also measure the top's moments with a heavy-duty custom-built trifilar pendulum, but there'd still be time-consuming measurements and calculations after the construction.
However, it would be nice to have human power take over. I imagine traction of the whip will be key so an average rope might not be ideal. If there is a rubberized material or similar traction type material that anyone can recommend, that would help. I can scale images of other whips from videos to get dimensions and play with what works/fails.
I fear for your top's beautiful paint job. The pole whips in the video jim linked above look promising to me. Strips of leather or vinyl or heavy-duty inner tube come to mind for the soft ends.
With your top's shape, the whippers will need to land their blows near the widest diameter to be effective. Judging from jim's video and the large muscle groups involved, could be a challenge (think golf). Cylindrical whipping tops present a much bigger target area.
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Where in NYC?
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My answers to fill in the needed information maybe too vague, but here it is: Max diameter is 56cm off the deck. Wall thickness is fairly consistent 22-23mm except where it's not. The inside is a smooth curve matching the outside that flairs to meet the solid tip, tip is 20cm tall. The rings that make the crown are thicker do to limitation of stacked laminated octagon shapes that make the turning blank. Stack laminations are Pine 2x4's, or 2x6 to meet the tip and crown needs.The bolt on top is 1" x 3.5" with nut and washer. The tip is a stair rail part off eBay probably 3mm thick, the wood is turned to match the tip and the steel is glued on. This is likely too vague to make accurate calculations on, but you've given insight on whips I wasn't aware of. Hopefully one of these days I'll coordinate someone with a tool to measure rpm.
In my limited experience with a 'normal size' whip top, I thought I was whipping the tip. Now I understand this was not so and that whipping the tip of my top would not work. Maybe a Big Whip Top build is in order. I will not make it anywhere near 200kg, since I would not want to deal with handling that.
The electric scooters for rent in Brooklyn are available through an app. Revel is the brand. Scooters are driven from point A to B then left. The next rider unlocks the scooter to ride from B to C. The app tells the user where the nearest available scooter is. They claim a top speed of 30+ mph, mid level chaos.
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My answers to fill in the needed information maybe too vague, but here it is: Max diameter is 56cm off the deck. Wall thickness is fairly consistent 22-23mm except where it's not. The inside is a smooth curve matching the outside that flairs to meet the solid tip, tip is 20cm tall. The rings that make the crown are thicker do to limitation of stacked laminated octagon shapes that make the turning blank. Stack laminations are Pine 2x4's, or 2x6 to meet the tip and crown needs.The bolt on top is 1" x 3.5" with nut and washer. The tip is a stair rail part off eBay probably 3mm thick, the wood is turned to match the tip and the steel is glued on.
Thanks! That new data gives me a pretty good idea of Dorothy's mass distribution. My hollow spherical cone model is starting to look too crude, but not giving up quite yet. Still hunting for subtle model or spreadsheet errors, and better geometric approximations would involve much nastier math.
Hopefully one of these days I'll coordinate someone with a tool to measure rpm.
Since Dorothy's dots are evenly spaced and contrast well with their background, the only tool you need to get speeds is an inexpensive handheld laser tachometer. I like this one for its ergonomics and one-handed operation via the Auto button:
https://www.amazon.com/Ehdis-Digital-Tachometer-Non-Contact-Reflective/dp/B0765XP9LS/ref=mp_s_a_1_1_sspa?crid=2UULHU9TTHNUG&keywords=laser+tachometer&qid=1697322328&sprefix=laser+tachometer%2Caps%2C164&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfYXRm&psc=1
If there are 8 dots along a given circumference, just keep the laser pointed there and divide the RPM reading by 8 to get the top's spin rate.
I rely on these tachometers quite a bit in my own topmaking, and I think @Iacopo would say the same. For a given top and starting method, just knowing the actual operating speeds (from max launch to toppling speed) can help a lot when optimizing for spin time or play value or a certain optical effect or spin-down behavior.
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I rely on these tachometers quite a bit in my own topmaking, and I think @Iacopo would say the same.
Yes I do, when they are tops for the longest possible spins, in my case.
Comparing the spin times is the simplest way for to evaluate the best tops but I prefer to use the tachometer, for to have more complete data and for to understand better the reasons that a top spins longer than another one. With a tachometer I can essentially evaluate four different parameters: the starting speed, the toppling down speed, the spin decay at high speed, (which is related mainly to the aerodynamics), and the spin decay at low speed, (related mainly to the tip friction).
These data of different tops allow for a reasoned comparison and help to improve the design of the top.
I am finishing a couple of new tops in these days, they are tops for longest spins, I will show them here soon.
It was a difficult year for me, (too much work), and I never stopped making tops for so many months before. I hope that this will not happen again because I love making tops, also I have some new ideas that I want to try.
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I rely on these tachometers quite a bit in my own topmaking, and I think @Iacopo would say the same.
Yes I do, when they are tops for the longest possible spins, in my case.
Comparing the spin times is the simplest way for to evaluate the best tops but I prefer to use the tachometer, for to have more complete data and for to understand better the reasons that a top spins longer than another one. With a tachometer I can essentially evaluate four different parameters: the starting speed, the toppling down speed, the spin decay at high speed, (which is related mainly to the aerodynamics), and the spin decay at low speed, (related mainly to the tip friction).
These data of different tops allow for a reasoned comparison and help to improve the design of the top.
I am finishing a couple of new tops in these days, they are tops for longest spins, I will show them here soon.
It was a difficult year for me, (too much work), and I never stopped making tops for so many months before. I hope that this will not happen again because I love making tops, also I have some new ideas that I want to try.
Well put. Our tops, construction methods, and spin times are worlds apart, but we go after longer spin times in much the same way.
LEGO construction opens up a vast new design space for tops, and it's fun to explore. That often means prioritizing behavior or appearance at rest or speed over spin time. But I still make every design spin as long as it possibly can. A laser tachometer's a big help — especially when trying to lower critical speed.
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Tall whip tops are not easy to keep upright:
Considering how fast the drill got it spinning, this was somewhat of a failure. This might be an unmodified tank. Perhaps with a better tip it could have worked better.