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Great tricks and very informative video! I appreciate the information and explanation.
After watching your video, I googled ‘Moment of Inertia’ again (which I learned about here on these forums) to try and understand what it actually meant to the overall feel of the yo-yo. Wikipedia provided 2 .gifs that really helped me understand that: Higher MOI = More stability, but slower.
The below .gifs are if Mass is the same across designs. I like how you talk in your video about Total Mass as an important factor in the Sunbird’s design compared to the Hummingbird. Anyways, if Mass is the same across designs, then the below is true.
The Solid Beige Sphere has a Low MOI and is very fast; the Hollow Green Cylinder has a High MOI and is very slow:
The Yellow Even-Mass Distribution Cylinder has a Low MOI and is very fast; the Red Rim-Weighted Cylinder has a High MOI and is very slow:
The Sunbird and Hummingbird, although they differ in total mass, are excellent examples to use to investigate this. Would you happen to have their Moments of Inertia?
Also, since Acceleration and Stability are negatively related, I drew the bottom graph wondering what their function truly looks like. Other variables to consider plotting as a 3rd z-axis could be: MOI; width; mass; radius; a function of width, mass and radius (maybe MOI represents that already?):
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What makes a yoyo fast?
The fast forward button.
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What makes a yoyo fast?
It wants to shed a few grams.
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What makes a yoyo fast?
Your hands.
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Great video and very informative.
If I have learned anything from RGB LEDs in a gaming PC:
What really makes a yoyo faster is a flashy splash colorway of course. (About 10% speed increase)
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Everything you said is absolutely correct and your analysis is awesome! I don’t really know the MOI tho haha. As for the perfect combination I would say it depends on the player, and I am more of a throw the yoyo myself depends on feel kind of guy rather than pure numbers, our manufacturing team got that covered haha.
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MoI only affects acceleration out of your hand, not once it’s already spinning and on the string. At that point that rotating mass serves primarily to keep it spinning on plane.
Steel rings allow a higher MoI with a lower mass, which is why yoyos like the Hummingbird work. If you try to get that same mass and shape with a monometal you’ll end up with something that tilts super, super easily.
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I’d be shocked if he posted the MOI for his yoyos lol.
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the acceleration of a yo-yo should only depend on the mass of the yo-yo, not the MOI.
The effects of MOI on the translational motion of the yo-yo should be negligible when it’s not rolling on a surface.
Those examples on Wikipedia refer to when the friction between the rolling object and the floor present a torque
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Just remember.
The slower ‘you’ are.
The faster your yoyo will seem.
all my yoyo are extremely fast…
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It’s at least 5. Five moments.
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Hmmm…so the amount of caffeine isn’t the greatest factor in how fast a yoyo is! Sheesh…guess I have a lot more to learn. 
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Depends on how many flame stickers you put on it.
Hence why the Pyro is the fastest yoyo in existence.
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It’s all about how large the radius and mass (more importantly distribution of mass) is.
Assuming each of the 4 objects above have the same amount of mass, the ‘Hoop about symmetry of axis’ design, where it places most of the mass at the edge from a central point (reminds you of a bi-metal design doesnt it), gives the formula with the highest amount for moment of inertia (I).
Assuming all yoyos with similar weight have placed the mass at the edge, the one that has the longest diameter (ie larger radius) will have a significant jump in spin time; since radius is squared before it gets multiplied to the mass. This is why the Edge Ultimatum spins for a long time, because of its large diameter - even though it’s only a monomental and weights at only 63g, but the weight is concentrated at the edge. Same goes for Shion Araya’s radius line, the Converge, and even the YYR Almighty (pom body, very large diameter, metal weight focused right on the edge)
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Moment of inertia is not a measurement of how fast a yoyo spin (since I realized this thread is about What makes a yoyo fast).
Moment of Inertia is a measurement of how difficult/resistant a rotating object is from having its rotational velocity change. So if you give a yoyo a good strong throw, it will spin pretty fast. However, it will start to slow down over time obviously.
But if it has a higher moment of inertia, it will take longer for it to slow down. Of course during actual play, if the person is very good and can minimize the string from rubbing against the walls of the yoyo during execution of a combo, then the yoyo will continue spinning longer due to minimal friction
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Ramadan
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great video. well thought out, and great points for discussion. this also illustrates why reviews can be very subjective, and why i tend to not rely on them too much. you get out of a throw what you put into it - and that’s not equal across all of us. i’ll tend to discuss my ‘experiences’ with a throw, and get with my circle of folks that tend to like the same things as i if i’m looking for something new
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