U-joint non-linearity demonstration

[aeh5040]

A demonstration of what happens if you don't align your U-joints correctly...

[oracid]

I am very interested, this sounds very important.

But can you explain to me what is a U-joint?

I guess I understand, but it is not clear to me why the red one is much better.

Edited December 13, 2015 by oracid

[aeh5040]

I am very interested, this sounds very important.

But can you explain to me what is a U-joint?

I guess I understand, but it is not clear to me why the red one is much better.

A U-joint (or universal joint) is this:

It enables rotation to be transferred through an angle. However, it has a disadvantage that the rotation is not quite linear - if the input rotates at a steady speed, then the output will be slightly faster at some points of the cycle and slightly slower at others. With one joint this is barely noticeable, but with several the effects can add up.

The two rings each contain eight very large U-joints (they are actually inside out - the colored square is the equivalent of the small piece in the middle of the Lego part above - but this makes no difference to the operation). The only difference between red and blue is how they are connected up. In the blue ring, each grey section contains a twist, so the non-linearity effects add up, to make a big effect at the top. In the red one, the directions alternate, so the effects cancel out.

If you you use several U-joint in series, you want to line them up as in the red one!

Edited December 13, 2015 by aeh5040

[jorgeopesi]

Very interesting everything about u-joints .

[KirTech LAB]

Great presentation of the basic principle!

[Zerobricks]

Well done! Great idea with solid internal structure too.

[MajklSpajkl]

That is a really nice sculpture to look at, I'm already counting my #6 connectors ;-)

[higgins91]

good demo ! thank's

[OneMoreRobot]

Nice demonstration -thanks

Perhaps you could show 2-3 u-joints connected together correctly & incorrectly referencing the indicator groove on each end for the folks who don't understand

Cool model as well :-)

Edited December 13, 2015 by OneMoreRobot

[Zimix]

Well done, another mechanism which specially maniacs of aligning stuff should really consider.

Never not align U-joint unless you know the effect.

Edited December 13, 2015 by Zimix

[kieran]

Fantastic, looks nice in its own right, but illustrates an important point as well.

[rollermonkey]

Nice demonstration -thanks

Perhaps you could show 2-3 u-joints connected together correctly & incorrectly referencing the indicator groove on each end for the folks who don't understand

I understand, conceptually, but don't know about an indicator groove... Have I just accidentally been doing it right?

[aeh5040]

I understand, conceptually, but don't know about an indicator groove... Have I just accidentally been doing it right?

I was going to try to make a picture, but then I found it has already been done, on this forum (not a surprise, really). Check out:

http://www.eurobrick...showtopic=49999

The first one here is what you usually want (as in my red ring):

Edited December 13, 2015 by aeh5040

[BusterHaus]

Great demonstration!

[rollermonkey]

Oh, interesting. I'd always just thought those grooves were for reducing the friction between the axle and the various joints.

[JM1971]

I did it wrong once and tore a u-joint apart, they are hard to replace too becuase lego don't sell them individually and you can only get mostly old ones on bricklink, the ones that crack on the axel connection.

Its no joke people, look after your u-joints, this guy knows his stuff.

Edited December 14, 2015 by JM1971

[oracid]

I put this in a corner of my brain.

Thank you so much.

[Anio]

"U-joint non-linearity demonstration"

And this is why there are CV joints...

[lcvisser]

Finally I understand. I've read many times in various topics about "properly aligning the u-joints", but never realised the implications of it until I saw this video. Many thanks!

[RangGagaGing]

I did it wrong once and tore a u-joint apart, they are hard to replace too becuase lego don't sell them individually and you can only get mostly old ones on bricklink, the ones that crack on the axel connection.

Its no joke people, look after your u-joints, this guy knows his stuff.

Hi there,

try looking for missing parts in the service area...at least in Germany I could easily add u-joints to a shopping cart.

[pgplay]

Nice, and clear presentation, thanks for that, didn't think it mattered how they are aligned.

[PeterF]

Very nice demonstration!

For those who did not see it yet, Splat also demonstrated this effect very clearly:

Edited December 14, 2015 by PeterF

[TheNextLegoDesinger]

let me guess the second one isn't aligned proprely

[Limga]

And this is why there are CV joints...

Do you say about this joint? TLG call it CV joint, but in fact it and U-joint have the same principle, so it is not correct to call it "constant-velocity" joint.

[pgplay]

Very nice demonstration!

For those who did not see it yet, Splat also demonstrated this effect very clearly:

Now I see why some of the mocs seam to be driving in "waves" or with some kind of hasitation