Just bought a Yelets from One Drop and am loving it so far. Also bought some Format C brass side effects for it too. Tested them both out and i definitely feel the difference in weight. What are the advantages and disadvantges of it being heavier or lighter? Also in your opinion, what would be the better side effect (you can suggest a different side effect other than the two I have currently). Thanks!
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The Format:C doesn’t have side effects, so I’m a little confused what a “Format C brass side effect” is.
Sorry I meant Code 1 brass side effects. 
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The advantage/disadvantage, to my way of thinking, is nothing more than refining your own personal preference. So when/if someone suggests a different side effect, they will be really sharing based on their preferences. Which isn’t a bad thing. I have been on the forum for a while and I have identified those that have similar preferences to my own. When they get excited about a yoyo, I know I most likely will too.
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I guess probably, but would a heaver yoyo result in a longer spin time or more stability?
Heavier as a result of the side effect change I am referring to of course.
It’s really only changing center weight, so “technically” less is better, but it’s all about your preferences and what you like
so go out there and learn more about your preferences 
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Adding mass to the center shifts the distribution of weight away from the rims, lowering gyroscopic force (i.e., stability). Adding mass also adds inertia and momentum to the yoyo as a whole, which can be good or bad depending on how much mass it has to begin with and how much inertia/momentum feels good to you.
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ahh Physics…who would have thought that would have real world applications 
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Ah, so that makes me feel more comfortable using the lighter side effects because I would prefer more stability in the yoyo. I think im gonna stick with the lightweight ones for now, then when im more used to the yoyo, im gonna try to shift to the other ones and see if I prefer those. Thanks for the technical answer, that really helped shed light on my question!
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definition of physics:
study of the natural world
Since the side effect can’t actually remove weight from the rim, it will have a close-to-zero change in stability, or at most a very slight increase. Along the same line, lighter side effects don’t increase stability at all. They just make the total mass lower.
It will certainly make throwing the yoyo feel different, because your brain kind of combines the sense of the throw, the weight of the yo, and the mass mo(ment of inertia… gotta try the rhyme) into one feeling of “heavy” or “light” or “good” or “bad”.
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Right. And I didn’t say it removed weight. You must read what I said more carefully. I said it shifted the distribution of weight away from the rims. In other words, if a yoyo with light side effects has, for purposes of discussion, a roughly 50/50 distribution of weight (center/rims), then adding heavier side effects might shift that distribution to something more like 60/40. That change in ratio will effect the gyroscopic force.
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The advantage is having one yo-yo that can play like another.
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A little physics, for what it’s worth:
There are two inertias that are important for yo-yos (and other objects).
- weight/mass. This is the “translational inertia,” and determines how hard it is to move (accelerate) the yo-yo from one place to another.
- rotational inertia, also called “moment”. This controls how hard it is for the yo-yo to change its spinning. This means the yo-yo will not want to slow down, and will not want to tilt (since tilting changes the orientation of the spin in space). So this makes it both long spinning and stable.
Everything affects the total weight/mass. Weight at the rim greatly affects the rotational inertia, and weight at the center doesn’t affect it at all.
In general, you want a large rotational inertia, and less total mass. This is the reason yo-yos are rim weighted. Of course everyone has different preferences.
Adding weight to the center adds to the weight, but not the rotational inertia (much). This makes it harder to move, and feel heavier (because it is). While it doesn’t affect the stability or spin directly, it does some in indirect ways. More weight means more force on the bearing, and so more friction. Also, other forces, such as bumping the string, will be larger, knocking the spin off its otherwise constant orientation.
This is just a dime store physics explanation, and I’m sure there are nuances I’ve not thought of.
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This is not entirely true. The center weight is usually there for float and feel- as too much rim weight is boring sometimes.
Center weight does have benefits though,
Such as staying stable during low rpm spins etc.
So back to the topic, its still all in preference.
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To add to this, and also touching on the seeming disagreement about whether center weight “remove” stability, its worth looking at the geometry of a yoyo on the string, say a trapeze.
Even though heavier side effects technically doesn’t remove rotational inertia, but by increasing the total weight, in order to maintain the same geometry of the yoyo on the string, the tension on the string have to increase and so when the yoyo wall leans on the string, the string is less willing to give, and would be more prone to move. Also the heavier yoyo would have much more linear momentum travelling at the same speed as a lighter yoyo, so when they land on the string and the wall hit, it would also be more prone to tilt since a greater impulse is applied to stop the yoyo, and the off axis impluse would be proportionally larger. But all of this depends on the geometry of the string, imagine doing a vertical boing E boing, the two string tension are affected by how hard your hands pull and not the weight of the yoyo.
I think another factor that affects perceived “stability” is how much the yoyo wobbles, especially since how low wall modern yoyos are. If someone good at math can explain what are the factors that contribute to wobble to me would be great. My guess is some sort of ratio of rotation inertia over the axis of the axle and over the axis of the yoyo string. I was trying to do the math for this, and saw stuff like precession and nutation and gave up. I wonder whether these ever plays a role (i know precession plays a role on gyroscopic flop and thumb grinds), but how about nutation? is THAT the wobble, it looks a bit slow to be the wobble.
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Adding or removing center weight will barely affect the gyroscopic force.
Let’s take a brass Markmont Dome (maybe it might be called a markmont.dome today) as an example. This one is about 0.1g too heavy but it’s really close. Real ones are about 2.66g.
Note that the moment of inertia around the spinning axis is 28.561 g/m^2.
Now, imagine a PLA yoyo that is 60mm in diameter and has a mass of 26.8g.
The moment of inertia here is 12,290 g/m^2.
Moment of inertia is an additive property - if you have a system of multiple bodies rotating around the same axis, you can add their moments together. In this case, adding the dome to the yoyo body results in a moment of 12,318 g/m^2 for the assembled half.
By adding the domes, the yoyo is 9.92% heavier, and has 0.228% more moment of inertia, despite having a lower rim to center weight ratio than the half without the axle system.
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Very Cool! Could you please expand on how changes in moment of inertia change the feel in play?
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Thanks for this great analysis!
Another way of thinking about this is that moment of inertia (or rotational inertia) depends on the distance from the center squared. In effect this means that the distance form the center is real important. Weight very near the center has almost no effect on moment of inertia, but does affect mass, as @MarkD has shown here.
I’m surprised moments of inertia are not listed with other statistics. Certainly not as easy to measure as radius, width, and mass, but quite important.