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kweso

Rigging double hinge

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Hey,

how would you setup this:

 

I want to animate the rotation of Spline B where Slpines C and D rotate as they conected to each other like with hinches. I do not want/need dynamics. Just have C and D rotate automatically when I rotate B.

 

See attached files.

 

Thank you very much!

Screenshot_20200720112523.png

hinchtest.c4d

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I have never heard of a 'Hinch'. I suspect you mean 'Hitch' or 'Hinge' but still not totally sure what mechanism you mean. Can you upload some photo reference ?

 

CBR

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I am not sure what you are trying to do exactly, but I am guessing it is creating what is known as a 4-bar linkage (shown here in Blender).  If so, then you could try using dynamic connectors (hinges) .  The trick is getting the driver link (the one that makes the full rotation) to correctly drive the rocker link (the one that just rocks back and forth).  Not sure you can do that with straight Expresso unless you get into the kinematic equations and that is why I suggest using dynamic connectors where all that math is done for you.

 

Now, the other trick is to insure that all the link lengths are correct.  If not right, then the mechanism will jam...that is, NO link will be able to make one full rotation.  There is a simple law for this in 4 bar linkage design called Grashof's law to insure that at least one link in a 4 bar linkage will make a full rotation:

 

Sum of the lengths of the shortest and longest link must be less than or equal to the sum of the lengths of the remaining two links

 

Now there is a lot that goes with this such as what is the fixed link, where does the shortest link go, etc.   Each choice creates different results.  For example, if the shortest link is the fixed link then the two links adjacent (or those connected to it) will be able to make full revolutions.  This is called a double crank mechanism as you have two links making full rotations.  If the shortest link is adjacent to the fixed link, then only the shortest link will make a full revolution (the other adjacent link just rocks back and forth).  This is called a crank rocker mechanism.  Things get weird when the shortest link is opposite the fixed link (eg. the only link not directly connected to the fixed link) as the shortest link is the only link to make a full revolution while the other two just rock back and forth (reference the 1:34 mark in the Blender video) --- thus called the double rocker mechanism.

 

There is a whole area of mechanical engineering devoted to kinematic chains.

 

I hope this helps.

 

Dave

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I'm not an engineer, but if you enjoy this sort of thing you might like this free linkage designing software.  I do : )
It's amazing what you can do with the right set up : )

 

Linkage software

 

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Here's my 1st attempt at the video linked by @3D-Pangel using dynamics

 

 

the initial setup was quite hard

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13 minutes ago, jed said:

Here's my 1st attempt at the video linked by @3D-Pangel using dynamics

 

 

the initial setup was quite hard

You nailed it.  I did not think it would be easy....I just knew that dynamics would be required.  You know, there could be a need for a plugin that does this. Just drag and drop the link objects into 4 inputs on the plugin interface:  Driver link, Fixed link, Link A and Link B.  You also input the rotational speed of the driver link.

 

There is a whole area of study on 4 Bar Linkage Coupler Curves (reference here).   The curves drive all sorts of mechanical engineering designs. Right now, there is no general purpose plugin that I know of that that makes creating these curves in 3D or which makes visualizing their mechanical applications in 3D.

 

You already did the hardest part!    Incorporate the inputs on link types as discussed above, stick a bar out there to some point that makes the coupler curve and add a path tracer and you are there!

 

Dave

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1 hour ago, MikeA said:

I'm not an engineer, but if you enjoy this sort of thing you might like this free linkage designing software.  I do : )
It's amazing what you can do with the right set up : )

 

Linkage software

 

I wrote a 4 bar linkage simulator in college (way back in 1985 -- in fortran....using punch cards).  It almost made me want to quit engineering and study basket weaving.  I can't imagine writing a general case software program like this with n-linkages.

 

Dave

 

 

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@Jed: it's an odd co-incidence that this topic has come up - did you see my private message of a couple of weeks ago?

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Posted (edited)

4-bars.thumb.png.7d5b128cfc893981d07184cc1358cee7.png

 

My method - the lower bar doesn't move, so can be collider. Right bar is also collider and rotated using XPresso.

 

I aligned the 2 left hinges, then drew circles the size of top + right bars. Where they crossed was the line-up point for top right hinge.

 

I realigned the parts a bit

 

4bars_2.c4d

Edited by jed
scene file added

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