+Ken Wright Me neither, it's got more puns thus far. :)

Yes that would be useful

Thank you for the criticism! You are not the only who have that problem, as I too have that problem! It is most certainly something I will compensate for in the future. And as for the question, I ABSOLUTELY want to do a video explaining the design characteristics of different bearings, as I have omitted that concept very largely and focused mainly on pads and axles for the two videos that are currently out. There are two main reasons that come to mind for why a company may choose to use one bearing over the other. They are cost criteria, and performance criteria. On the topic of cost, if D sized or A sized or E sized or just some freaky custom sized bearings are readily available to you, and cheap to acquire, it makes sense that you might be willing to eat the loss created by yoyoers who don't want to own a yoyo with an incompatible bearing size in exchange for the savings in initial manufacturing. This was especially prevalent in the earlier days of the rise of the all metal yoyo (early 2000s to mid 2000s) when there were still competing standards for what the most commonly used bearing would be, especially in the European and Asian markets where transaxles were giving way to whatever commonly sourced metric sized bearings could be found with acceptable performance. And on the topic of performance, in the extra lesson #1 video, I mention how the axle will bring a yoyos rim weightedness down because it's a big piece of denser metal at the center of the yoyo. The same can be similarly said for bearings. Smaller bearings are usually lighter (with some exceptions due to weird quirks of bearing design and different material choices and all that jazz) which means that higher relative rim weights are possible with smaller bearings and shorter axles. Additionally, yoyos with smaller bearings can spin faster, due to the limited speed at which a human can throw something coupled with the smaller "rolling diameter" that a smaller bearing allows a yoyo to have (just like how a smaller wheel on a car needs to spin faster for it to go just as fast as a big wheel bicycle). Interestingly, the effect that uniformly higher rpm has on the yoyo is not universally good or bad. The higher angular velocity tends to make the yoyo more likely to snag, thus requiring a slightly wider gap, as well as making the yoyo require a lower moment of inertia in order to "feel" like other yoyos of their desirable performance characteristics at that mass and diameter. Also, a yoyo with a higher average angular velocity tends to be harder to regen because, on average, it's more difficult to regen a yoyo that's coming to your hand faster. If my lack of concrete terms like "always" and "will" are indicative of anything, it is that; as indicated in the video; yoyos are quite complicated, even down to simple stuff like what bearing you choose to select.

Thank you. So, first off, if it was too long, and you still had to watch it twice, wouldn't you say that it really wasn't long enough? Should I have had a part at the end that was basically a TLDR? But, see, if I did that, the entire philosophy of why I made this video; that "people NEED to understand the reasoning behind this design in order to be able to use it properly" would be betrayed. Now for your next question there. Most bearings in the early days of experimentation were used either because they were cheap/easy to source and produced a good performing throw, or the specific characteristics of a yoyo such as cost, or performance requirements mandated a specific type of bearing. The Imperial used no bearing because it was cheapest to manufacture. The Proyo used either a wooden turned piece as a spacer in a plastic part on a cheap standoff threaded into a transfer molded nut because it was cheap (although not as cheap as the fireball, in my interpretation). The fireball was a pretty revolutionary design, as it used the compatibility of different materials by criteria of abrasion compatibility (see a table of "Wear Coeficients" if you wanna know more about that) and used a plastic bushing/stringholder that they called a "Transaxle" system which took the place of the proyos wooden central bushing (I don't know if later models of the proyo or other similar duncan designs switched to a plastic, but they might have).You'll see that almost no European yoyo companies that had their roots early in the ball bearing revolution use a "size C bearing" because a size C bearing is only a standard denomination in inches (it's 0.5 by 0.25 by 0.1875 INCHES) whereas a size D bearing is 11mm by 5 mm by 5 mm in the same measurement convention used earlier in this sentence (OD, ID, W). It makes sense if you are in Europe that you aren't likely to have imperial standard components in your short list of "parts I want to design my toy around." A lot of asian (Chinese mostly) companies used imperial bearings because they emulate US and European design trends and there's rampant intellectual property theft that occurs between American firms that have their parts made in China, and identically constructed Chinese firms that are usually able to undercut the American company using the exact same components and bills of materials (see the history of the Segway for example there). I have used nearly every single bearing size that exists in my designs. I certainly think that with the renaissance of flowable response, companies should feel confident to try other bearing sizes once more. The biggest issue in doing that nowadays is that most bearing widths that have been used historically were customized for either responsive or semi-responsive yoyos. If your bearing width infringes upon the length scale of your "string width" then you can only do so many wraps around the yoyo with the string before it snags, as it gets awkward to try and have a gap that's bigger than the width of your bearing. The impacts on design that different bearing widths can have is immense. They all have different rolling friction versus radial load plots, and so they all slow down differently as you speed through them on faster tricks (applying more centrifugal force to be transmitted to the yoyo shafts through the ball bearing). You'll usually see certain designs which get better quality to them as more of those bearings are ordered by different industries. That's why so many machines and stuff use what are effectively SkateBoard bearings for their rolling elements, as they are so largely made that they are cheap in bulk and generally high quality. The larger impact on yoyo performance, however, is mainly due to the nature of how rotational velocity works. As you go out on the yoyos radius, the surface speed with respect to the string increases, and the inverse is true as well. This means that if you have a lower diameter bearing, but use the same amount of radial length of response and the same gap to the yoyo, it won't bind as well, purely because the friction at play is directly proportional to the relative velocity of the pad surface v.s the string. Now, one interesting thing to think about is how that trend CAN'T be true as you go to the lower limit of rotational speed. At zero rpms, the friction coefficient at play is the STATIC friction coefficient rather than the kinetic friction coefficient, and it is an observed physical law that the static friction coefficient is always higher than the kinetic friction coefficient. Therefore, there MUST be a certain rpm, and consequently, radius of bearing, at which the yoyo would be EASIER to bind with the same scale sized response pad rather than harder to bind; but that seems like something that I don't want to do the math on quite yet. Hope this answered your question.

Nope, nevermind, the subtraction of 1mm wasn't a part of the equation at all, I misread that.

Yep. Many companies.

Too long and you can't put the yoyo together. Too short and it won't be able to sustain the shear forces or be able to transmit bending moments of either a regular throw, or a ding. The conclusion here is to make the shaft as long as you can, but not too long. The reason I picked the length that I did is because I calculated how much the seat could possibly deform if you tightened the yoyo a lot; which would subsequently bring the two faces of the shaft on each half together as the yoyo deformed from being overtightened.

+Ze'ev Yehuda If you've ever wondered why that secondary step was even there in the first place, or even why it is as deep as it is, the reasoning for it is that if it were any deeper, it would become the structural weakpoint for the throw, and any shallower would make it so that the air swirling around the inner race of the bearing wouldn't have enough volume to swirl around and properly move air around the bearing. It is a relatively arbitrary dimension, but it's there for a reason.

+ZachTheSloth Why is it important for the air to swirl?

+evilbee Two reasons, one of which is more important than the other. The more important one is that when a torque is put on the bearing, the outer race of it may deflect slightly, and there needs to be space made to assure it does not hit the side of the yoyo. The less important one is that bearings without proper space to allow the free flow of air tend to lead to a buildup of particulates in a weird feat of fluid dynamics. A similar effect to the eyes of hurricanes can be seen, wherein particulates that find themselves near the center of the yoyo have an easier time just staying there than they would getting out. This is one reason why shielded yoyo bearings coupled with outer bearing wall diameters too small for household particulates to escape from tend to lead to yoyos which accumulate foreign particles. And the definition for "too small" is ultimately the average boundary layer height for the air flowing past the yoyo bearing at that diameter, which you can learn slightly more about here. en.wikipedia.org/wiki/Boundary_layer However, let me warn you of this; fluids are complicated; so complicated, in fact, that we as a species will understand the inner workings of dark energy and the nature of the universe before we can accurately predict the flow of syrup in a bendy straw.