[HELP] Generic Building Help Topic

[Stereo]

6 minutes ago, ukbajadave said:

Is there a trick to aligning big CV joints like universal joints? My specific example is this new CV to UJ

It's effectively inside out from the U-joints, so you want to match these pins to the orientation of the holes on the U joint, on the intermediate shaft with joints at both ends. (same as 2 U joints want them to match)  I think that means your picture is correct.

[gyenesvi]

11 minutes ago, ukbajadave said:

Is there a trick to aligning big CV joints like universal joints? My specific example is this new CV to UJ

Why would you need that? As far as I understand, the name CV = Continuous Velocity means exactly that it does not have the oscillating velocity problem of U-joints. So there is not need to align them. And I guess when you have one CV and one UJ, it still does not matter how you put them, since one of them is continuous, so there's nothing to align with. But anyway, when I use two CVs, I align them to the same orientation just to make it look better.

Edited March 12 by gyenesvi

[ukbajadave]

@Stereo That seems logical so I'll do that, cheers 

6 minutes ago, gyenesvi said:

Why would you need that? As far as I understand, the name CV = Continuous Velocity...

Interesting point, is part 52731 Large CV Joint actually a constant velocity joint or instead a larger universal joint? I mean sure, Lego calls it a CV but on actual cars they are a little more complex and full of ball bearings and stuff.

[Stereo]

Oh, I never looked closely to the small/large ones to notice they swapped the "male"/"female" parts, so the one with the axle-holder has the nubs on the large version, and the axle has the slots.  They're still mechanically the same universal joints, just with sliding instead of a 3rd moving part.

 

Just to confirm things I wiggled the 948L skidder around, since it uses a single one instead of a center differential, and as expected at 0/90 to the steering axis they stay in phase, but if the CV joint is at 45 degrees, steering it will make one of the axles roll forward while the other stays still.  It's lego so there's enough slack in the gears it doesn't really matter for driving of course.

Edited March 12 by Stereo

[gyenesvi]

12 minutes ago, ukbajadave said:

@Stereo That seems logical so I'll do that, cheers 

Interesting point, is part 52731 Large CV Joint actually a constant velocity joint or instead a larger universal joint? I mean sure, Lego calls it a CV but on actual cars they are a little more complex and full of ball bearings and stuff.

Yeah, I have been thinking about that too, whether it is just called like that as it approximates the real thing or is it actually close to constant velocity.. I'd tend to think that out of all the lego joints, the new large CV joint has the most stable velocity though. But yeah, I guess the best is to align as @Stereo suggests, can't really harm things.

4 minutes ago, Stereo said:

Oh, I never looked closely to the small/large ones to notice they swapped the "male"/"female" parts, so the one with the axle-holder has the nubs on the large version, and the axle has the slots.  They're still mechanically the same universal joints, just with sliding instead of a 3rd moving part.

Upon looking up a video of a real CV joint, sure they are more complex, but I'd think the actual conceptual difference between the U-joint and a CV joint is exactly that sliding motion instead of the 3rd moving part. I'd tend to think that the fact that the large lego CV joint has the spherical surface that slides as it rotates is what allows it to rotate without oscillations. It seems to me that a real CV joint also has that sliding in it, albeit with more nubs (3-6 instead of 2), and the nubs are actually ball bearings to make it smoother. But the principle seems the same in the lego version I guess.

[ukbajadave]

I vaguely remember a youtube video where someone had lots of universal joints out of alignment to demonstrate the cumulative effect. I only have 4 of the new bigger "CV" so probably too few to be  noticeable, but if someone else has lots how about an experiment?

[howitzer]

2 minutes ago, ukbajadave said:

I vaguely remember a youtube video where someone had lots of universal joints out of alignment to demonstrate the cumulative effect. I only have 4 of the new bigger "CV" so probably too few to be  noticeable, but if someone else has lots how about an experiment?

This maybe?

I think the CV joints are actually constant velocity, it's the third part in the middle which makes an U-joint not constant velocity.

[ukbajadave]

@howitzer That's exactly the video I was thinking of!

Whilst searching for it I found This 2015 Eurobricks thread where people are discussing whether or not Lego CV joints are actually constant velocity so it seems we are not the first 

[Stereo]

56 minutes ago, gyenesvi said:

Upon looking up a video of a real CV joint, sure they are more complex, but I'd think the actual conceptual difference between the U-joint and a CV joint is exactly that sliding motion instead of the 3rd moving part. I'd tend to think that the fact that the large lego CV joint has the spherical surface that slides as it rotates is what allows it to rotate without oscillations. It seems to me that a real CV joint also has that sliding in it, albeit with more nubs (3-6 instead of 2), and the nubs are actually ball bearings to make it smoother. But the principle seems the same in the lego version I guess.

I suppose my argument is that you can always place a virtual 3rd part in the slider and it'll join to the 2 parts as it would if it existed.  It's not the easiest thing to find good reference on but the ball bearings in Rzeppa joints are actually splitting the angle between input and output in half, and acting like a double U joint.  They don't stay fixed relative to either component.  And now I'm questioning the old 8880 "CV" balls too since that other thread brought them up.  Unfortunately I don't have that set to look closely at how it works.  I do have 8444, not sure it's the same part for its swash plate offhand.

Edited March 12 by Stereo

[2GodBDGlory]

1 hour ago, Stereo said:

And now I'm questioning the old 8880 "CV" balls too since that other thread brought them up.  Unfortunately I don't have that set to look closely at how it works.  I do have 8444, not sure it's the same part for its swash plate offhand.

Yeah, that uses the same system of parts, I'm pretty sure

[buzzy440]

Another pain on this MOC.
I do not understand how to hold the red coin and the 2 small yellow rings.
Thanks for your help

[Milan]

@buzzy440

Let's not open a new topic for similar questions about the same set/moc. Use the topic you already created today.
You can also use the main Generic Building Help Topic for questions like these.
I will merge it.

[tomek9210]

Hi, 

How hard is the Daytona shock absorber compared to the extra hard 9.5L yellow/black one?

Thanks!

[gyenesvi]

5 hours ago, tomek9210 said:

How hard is the Daytona shock absorber compared to the extra hard 9.5L yellow/black one?

Quite a bit harder, I'd say more than double; just compared squeezing 2 of the yellow ones vs a big blue one, and still the blue one feels harder to me.

[tomek9210]

Really the difference is so huge?

Thanks!