So 6061 is less dense than the 70 series aluminium, but at the same time they are softer.
Given that a lot of extreme weight distribution bimetals focus on making the aluminium parts lighter while trying to maximize weight on the steel rims, I wonder what aluminium is the better choice.
6061 is less dense which may give the impression that it’s lighter, but at the same time it’s weaker so it has to be thicker, so it can’t be as thin as the 70 series aluminium. As a result, if you are designing a 6061 + SS bimetal you’ll need more volume in the aluminium parts compared to when you would design a bimetal with 70 series aluminium.
So I’m wondering. Given the compromise between density vs structural integrity, what would end up with a lighter overall weight for the aluminium parts among the three different aluminium alloys?
Yoyos like the Edge Beyond/Infinity have extremely thin aluminium walls and extremely thick stainless steel rims. Despite their fat rims, the thin aluminium makes it possible for them to stay at a relatively light 64g weight.
I wonder if it would be possible to make them lighter by using a different aluminium alloy and making the walls even thinner. It seems like the wall thickness is about as thin as it can get with 6061 without compromising on durability, at least the for higher end Edge series yoyos.
Is there anyone here with design experience who can chime in?
Titanium > 7068 > 7075 (barely) > 6061, once you adjust for wall thickness/weight. Of course it will also depend on the exact design but its a rough estimate. To answer your question directly, yes you could get the walls thinner and overall lighter with 7077/68/Ti.
To do the math yourself, OneDrop’s rough estimate min thickness values are:
1.524mm for 6061
1.016mm for 7075
0.458mm for Ti6AlV4
7068 should in theory be slightly thinner than 7075.
A useful material index to think about is min thickness*density:
0.411 g/cm^2 for 6061
0.285 g/cm^2 for 7075
0.203 g/cm^2 for Ti6Al4V
This is basically the density for a given wall section.
Of course the entire yoyo isn’t designed at the minimum wall thickness, so there’s going to be lots of other geometry/design dependent factors, but this is the very general gist of it.
Basically if for a given profile you want to absolutely maximize your weight distribution, your best bet out of commonly used materials would be Ti+Brass. (Given “normal” yoyo dimensions)
7068 you can make as thin as 0.8mm, which gives it a clear margin over Titanium after density is taken into account. Luckily, it’s less expensive, as well.
pushing the limits of your materials is not always going to give to the best results. there is more to design than just the limits of a material’s properties.
most of the people that are buying a yoyo are whacking stuff, not playing over carpet (i REALLY have a hard time believing all yoyoers have carpeted homes they always play over all the time). smashing stuff happens… account for vibe… after it hits the ground once
You can take all these numbers and add 25% thickness for durability and have the same question at the end of the day - which one gives you the most per gram of mass?
… then you have flexibility, tensile strength, elongation, etc. other factors that on impact caused by stress/strain can/will effect the yoyos play, causing vibe, etc…
Thanks for the data! This is exactly what I needed. It seems like 7068 is pretty damn amazing. I didn’t know it had such high tensile strength. Judging by this data alone, it seems like 7068 is quite a bit better than 7075 in terms of tensile strength/density. I would love to see more 7068/SS bimetals and 7068 monometals with interesting weight distributions.
I’ve seen super thin walls on titanium yoyos capitalizing on its strength, and I wonder if anyone would end up making a super thin-walled 7068 yoyo anytime soon.
I also just remembered, but I’m also curious what yoyo designers think of magnesium considering it’s also light like aluminium and quite durable. I’ve seen a couple magnesium yoyos here and there, but I wonder why it isn’t as popular of a material in general.
I’m not sure how thin the walls on the hummingbird are, but they were brave enough to claim it might be the thinnest in their marketing copy. There’s a number of other 7068 bimetals out there.
I keep an UNPRLD Flash (6061+SS) on my shelf to always remind me that I don’t need 7xxx alloy to pull off a design.
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Grendel
(The Voice of All Grendel’s world wide.)
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However it is the correct answer for this question. Also only @fatguysnacks247 who Is an engineer remembered all the other effects on materials that most people just forget or don’t know. Elongation is my personal favorite, I used to do A&P and you have not lived until You’ve spent all night measuring bolt lengths because the freaking engine had to be flight worthy by 0400.
correct. durability isn’t just a number that just ends with a materials mass, it is a property of the material, along with many other properties, that when changed or effected can minutely or drastically impact the performance of a given material.
a ‘standard’ assumed/stated by someone in an industry for what THEY are comfortable with, likely through years of vigorous prototyping and testing, and then adopted bu a subset of an industry, does not make it an industry standard, nor does it change the yielding points and properties of a material you are working with.
your mileage may be different. your manufacturers mileage may be different. the quality of material you get from your manufacturer may be obscenely different than that from the manufacturer you are comparing to.
At the end of the day durability isn’t something you necessarily have to design for. If you’re really trying to push a design and don’t care about longevity, sometimes just because you can is a good enough reason, after all we’re designing toys here not aircraft.
A rule of thumb is good enough , if you wanted to be completely rigorous it would probably be relatively straightforward to simulate your design and optimize accordingly, but afaik no one puts in that much effort.
he knows i’m an engineer because he knows me. longevity is important because people… even pros… will hit a yoyo in the ground, sometimes a $500 yoyo on the first throw even if they’ve been playing for decades!!! if it was unplayable after that, that would be asinine to produce in any scale besides one…
good enough is for people that revel
in mediocrity, like ducking under the bar instead of raising it… and people that don’t care about the end users longevity of experience
Sorry if it wasn’t clear, but that was the first line of a joke, the second line is “They (or their friend) will let you know”
Good is not a super precise term, good can be in pure performance, good can be in “this design has a much higher A-grade rate”, good can also just be “this design looks cool”. At the end of the day pretty much every yoyo nowadays is good in whatever way the designer intended for it to be good. They all spin well either way.
, if you wanted to be completely rigorous it would probably be relatively straightforward to simulate your design and optimize accordingly, but afaik no one puts in that much effort.
