"PatDan" constant-velocity coupling

[aeh5040]

For those wishing to take a break from Porsche-mania, I offer this little MOC.

Some explanation: The standard way of transmitting rotation through a variable angle is the trusty universal joint.

However, as has been discussed here before, the universal joints do not have the constant-velocity property. If the input rotation is uniform then the output will be slightly jerky - faster and slower at different parts of the rotation. In some applications this can cause problems including vibration.

One possible solution is the double Cardan joint, which consists of two U-joints in series, aligned to be reflections of each other. (In Lego that means lining up the two slots on the middle axle). If the two angles are equal then this will cancel out the irregularity.

(If they are aligned the wrong way then the irregularity will be magnified!) I made these models a while ago to illustrate the difference:

However, the double Cardan does not completely solve the problem, for several reasons. The middle shaft still rotates irregularly, which means that it is accelerating, causing vibration. Also, to work properly, the two angles have to be equal. In a movable coupling this requires an extra linkage, which ends up being complicated and bulky.

Some other types of coupling ARE constant-velocity, such as the Rzeppa joint.

However, until recently, all such used sliding surfaces of some kind. This changed with the invention of the Thomson coupling, which is effectively two universal joints combined into one, with an internal "spherical pantograph" that bisects the angle.

As you can see, it is pretty complicated, and the pantograph part is quite small and fiddly. I did not manage to implement this in Lego yet.

Remarkably, a new coupling has recently been invented. The inventor calls it the "PatDan" coupling. This is constant velocity, and has no sliding surfaces. It is much more symmetrical, and arguably simpler than the Thompson coupling. For more information see http://www.pattakon....takonPatDan.htm It took a while, but I finally worked out the geometry, and the above is the result! A key property is that the central axle (yellow in my Lego version) bisects the angle between the main axles.

Edited June 6, 2016 by aeh5040

[Nalyd997]

Awesome work! I'll have to watch the video a couple more times though to figure it out

[BusterHaus]

It's a very well executed proof of concept, but I don't think it will be used in many MOCs, as is much too big to be integrated into a car or any other scaled model.

Have you tested how much torque it can transfer?

[Victor Imaginator]

Awesome, thanks for sharing. I spent a lot of time learning how various cv joints works some time ago, it's nice to see something new)

[PorkyMonster]

this is huge... but i'm totally impressed! Edited June 6, 2016 by PorkyMonster

[Appie]

I love it when engineers come up with new concepts and people make it into Lego. Great work!

[aeh5040]

It's a very well executed proof of concept, but I don't think it will be used in many MOCs, as is much too big to be integrated into a car or any other scaled model.

Have you tested how much torque it can transfer?

No, it definitely wouldn't be useful for actual Lego vehicles. It is much too large and weak for that. The purpose of the model is to show how it works. If it were made from real metal parts, there seems no reason why it couldn't handle high torque. So far as I know this has not been done.

[Jeroen Ottens]

Amazing contraption! And amazing indeed that we are still inventing concepts for situations that have been in a status quo for ages. Somebody must really have taken it personally

[BusterHaus]

No, it definitely wouldn't be useful for actual Lego vehicles. It is much too large and weak for that. The purpose of the model is to show how it works.

Mission accomplished, I am going to bed less stupid tonight. I was not familiar with this mechanism.

[DrJB]

Beautifully executed. I can't help but think of Euler Angles and Kane's Rates of Rotation ...

Any chance you can post 'static' shots of your contraption, for those of us tempted to build our own copies?

[miguev]

Stunning and mesmerizing!

[SevenStuds]

Definitely taught me something. Thanks for all the extra technical info.

[Blakbird]

Was the PatDan joint invented by Patpong ladies?

[aeh5040]

Beautifully executed. I can't help but think of Euler Angles and Kane's Rates of Rotation ...

Any chance you can post 'static' shots of your contraption, for those of us tempted to build our own copies?

I took some photos, but I was not very satisfied with them so I made an LDraw file! Getting the angles right was an interesting challenge. I would be interested if someone can make a better version - the inventor claims that the coupling can transfer rotation through angles up to 60 degrees with proper shaped parts, but I had to make compromises in the Lego version, so the angle is much smaller.

http://www.brickshelf.com/gallery/aeh/coupling/patdan.mpd

[LEGO Train 12 Volts]

Impressive topic and incredible solution!

[roppie11]

wow genius invention, and genius replication from lego! :thumbup: I took a look at the website but now i understand it even worse!look at this":anyways, thanks for sharing this and making an lxf file. maybe i understand it better if i make it myself(with your lxf file obviously) :laugh:Really awesome creation!

- edit: waitt and LDraw file, i have to figure out how that works :cry_sad:

Edited June 22, 2016 by roppie11