modeling an ellipsoid joint

[2ms1]

Could someone give me some pointers on how I might model an ellipsoid joint? The picture below shows the two halves of an artificial wrist, and that is exactly the type of joint I am trying to make.

I'm not sure on two things:
(1) How to make the faces perfect ellipsoidal.
(2) How to make the two pieces behave as an ellipsoidal joint in animation.

View attachment 2929

Edited by: 2ms1

 

[SRINIVASANIYER1]

I'm not sure on two things:
(1) How to make the faces perfect ellipsoidal.
(2) How to make the two pieces behave as an ellipsoidal joint in animation.

1. I dont know. (I would rather borrow a skeleton and scan it...

)


2. use a cam connection in MDX.

 

[Miko]

hi tomas...There is most important fact of continuity of merged surfaces there on the ellipsoidal solid..You shouldinforme us how exactly you need to controle your part(relations,reference curves,reference points,general frame and so on...)...I have done this ellipsoid with help of ISDX module....There are of course many ways how to create this kind of model..You can create same model with more (or less)features by BoundaryBlend Tool and reference points..As you wrote earlier, you have only student edition of WF 3..I have done my model in full official version of WF3 and this is the mainreason why I am not sure if you will be able to open it... anyway...One of those ways to create ellipsoid is next.. followthese generalsteps....


First you have to create three curves with perpendicular direction of ends..There on the pictures are red arrows, that mean the normal direction of thecurves ends...I mean normal direction to the Datum planes...(You have tocreate therein drawing module:complete ellipse and thereafterdynamically trim the section entities of the ellipse...)..Than just create surface between those four curves


Mentioned first step>


View attachment 2930


As you can see, there is another DTM for intersected curve..Do not forget that we want to observe mentioned continuity and this is the reason why we have to create this intersected curve there on the datum plane...


next step>


View attachment 2931


nowcreate two joinedcurves on the surface (COS) but with only one end which one will be normally directed to the DTM's....


View attachment 2932


Now trim the highlighted surface according to picture above....


Next step will be creting another surface by four curves ... This kind of creating the surface allows us to create tangent continuity between surfaces... yellow arrows mean the tangent continuity between surfaces...


View attachment 2933


now just create a copy ofthe style featurebut thereafeterdo not forget to merge them together...


View attachment 2934


after mirroring all eight quilts>....


View attachment 2935


OK.. nowlook at the highlighted area..This section is mostly issuable to define....As you can see there is tangentcontinuity between surfaces (G1)..Look at thestripes... With help of special Zebra analysis:we can pretty simply evaluate the wholecontinuity of surfaces....Thesmoothness of surfaces is strictly needed for mechanical joint in Mechanism Design eXtension module...If you will need some help with defining the connection of this part just create another new topic but of course in suitable department ;-) .....
Edited by: Miko

 

[wsylvester]

1. you can create the ellispoid with 3 curves to drive5 curves by equation


one curve is the 360 degree ellipse;


ratio=minor/major
x=major*cos(t*360)
y=major*sin(t*360)*ratio


the other are 180 sections


boundry blend > first direction.. the 360 ..2nd direction the other 4 curves


solidify


2. connection...hmm just how much further could i turn my wrist if i didn't have this skin and stuff to restrict it ;-)


I can email you student files pm me

 

[2ms1]

wsylvester, what do you mean by creating it with three curves to drive 5 curves?


Also, why only one being a 360 section rather than all three?

 

[wsylvester]

it's in that file I sent you

 

[design-engine]

that looks just like one of my tutors. Perfect answer!

 

[mjcole_ptc]

This can be done with 1 Variable Section Sweep driven by 1 trajectory 1 or 2 Datum Graphs and a Variable Section Sweep with evalgraph relations only one Ellipse in a Datum Graph Split into the Q1 Quadrant using Split Curve and Toggle Geom.

Step Through With Notes
Just click right arrow on screen and flip through the 4 pictures and read comments.

STEP 1: for VSS Using Single Trajectory
View attachment 4298

STEP 2: Create Datum Graph Feature XRAD
to controls RX based on RZ.
YRAD is a copied feature with sd4 relation modifed to use RY to control it's Max Radius RY vs RZ
View attachment 4299

STEP 3: Relations in VSS Section to control size of ellipse from its max at the middle to its min at point on end of sweep.
View attachment 4300

STEP 4: AND FINALLY THE PROOF is in the Reflection Analysis.
View attachment 4301

Hope you like this method I trusted Actual Ellipses more than equations which can be more easily screwed up. Why write relations that are already designed into the ellipse curve. No ellipses were harmed during the making of this part, I only split them for the graphs.

I originally tried the Multi Sketch Methods, Boundary Blends and even Style. But the Variable Section Sweep is much cleaner. Like the my one for the SGI logo created with single datum graph and one Swept Blend this method uses a lot fewer features.

Michael



Edited by: mjcole_ptc

 

[wsylvester]

I'm missing something... why the mirror?


I am able to do the complete surface thru eq without a mirror....does the zebra just awell... presse for time right now so can't post


8 curves total. .. 3 to set the size and 5 eqs... 4 being clones.. boundry blend and solidify


just curious

 

[mjcole_ptc]

WSYLVESTER,

For you and the rest of the Boundary Blend Lovers. Here it is in a single VSS without the Mirror. Variable Section Sweeps cannot start from zero area like a boundary blend but can finish with zero area hence the Mirror. When I came up with that method I was not thinking
"Outside Of The Ellipse". 0

Here is a solution using One Ellipse and one Variable Section Sweep
Here is a reduced size image Click link below to see whole image
SIMPLICITY IS_KEY

View attachment 4309


In my opinion the order of creation ease for these Ellipsoidal Features.
1. VSS Easiest to create and fewest features and provides good continuous curvature.
2. Boundary Blend Very Powerful but requires a lot of Set Up
3. ISDX May look cool and Allow you to create the Ellipsoid in 1 Feature. But then again how long does it take to set this up and provide good ellipses without 3 Sketches.

If anyone has a way to do it in Zero Features I'd love to hear of it.

Michael


Edited by: mjcole_ptc

 

[wsylvester]

oh i like vss too..

... certainily since they improved vss's UI





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