View Full Version : how to simulate Joints with Constraints???

12-12-2004, 03:15 PM
I think that's a hard one.
How do i get a result like this (http://www.home.datacomm.ch/xavy/HookeJoint.wmv ) within LW :confused:
I did this anim in SolidWorks with very little effort. I gave up trying to set up such a joint in LW. I can't figure out how to connect the objects to each other in the proper way.
If someone could set up a demo scene with a full functioning Hooke Joint (3 parts) would be great. :)

or give me some advice please.

See here if u don't know what a HookeJoint is? (http://www.tpub.com/machines/11g.htm)

12-13-2004, 12:36 PM
Any body??? can't believe it :(

12-13-2004, 01:52 PM
Just a quick setup... it works as you expect :)

unzip the files and move the directory to your content dir, load the scene file and moce the time slider. I didn't model the part located at the joint, but I think you can get the whole thing by looking at the expressions used :)

Feel free to pm me if you need help

Oops ! for some reason, the scene file doesn't have the .LWS extension, so you need to use a .* pattern to be able to load the scene

12-13-2004, 03:20 PM
But how the middle part rotates? That is the problem.

12-13-2004, 04:31 PM
ok I updated my scene (I added the middle part and the expression that makes it rotate properly)

12-13-2004, 05:59 PM
Hey Weetos:
That's much more than I'v expected :) Thank you very much.
I knew there is a way to do this with expressions.
I wonder if there is a method without the need to find the proper formula. I think of something like reduce the degrees of freedom of an object, like a real joint would do? however thanks so far.

12-13-2004, 06:38 PM
hmm I see what you mean ... I guess you can use limits (motion options panel) but I don't know if it could work that way. Solidworks and LW are two different worlds :rolleyes: but don't give up yet, there are 1001 ways to do things in LW, so I'm sure someone will come up with something better than what I got ;)

I'm going to try a setup using limits and see if I can make it work

12-14-2004, 06:02 AM
I think it should be possible to do this using IK. However, it probably won't be as stable as doing it with expressions/motion modifiers.

How is this setup in Solid Works?

12-14-2004, 01:33 PM
In SolidWorls it's a breeze.
-first select the mate function.
-second select the faces of the two parts (green) which should be connected.
SolidWorks then pops up a menue where you can select one of the possible conection behaviour.

Here u can see how the bolt is set to center in the hole (concentric mate). (i can now move and turn the bolt along his symetri axis. but any other movements won't work)

if i want the bolt to be flush with the bar (Coincident Mate). I simply select the mate function again and select the upper face of the bolt and of the bar (green). (now rotation along the sym axis is the only possible motion)


P.S. that's a very fast and easy way to set the constraints between parts or simply to put things together.
P.P.S. in my HookeJoint example it's not only possible to move the knob. it's also possible to rotate a part of the joint and the handle will follow.

See this tutorial to learn how it works exactly (http://www.me.cmu.edu/academics/courses/NSF_Edu_Proj/Statics_Solidworks/MATING.htm)

I hope u can follow. It's a little bit challenging for me to explain such thing with my crappy english.

I think something like this would be great to have in LW. Not only to animate but also to put mechanical stuff together.

12-15-2004, 03:49 AM
yeah it seems so easy to do in SW, I'd love to see this in LW. like having presets for joints with premade rotation/move limits depending on the type of joints/connections (pivot 1 axis, pivot 2 axis, translate 1 axis and so on. Would be quite useful for mechanical stuff. But I guess this is not the kind of things (mechanics simulations/designs) LW is mostly used for

12-15-2004, 06:28 AM
here is an IK set up for Universal joint.
You can animate the rotation and the oriantation of the joint.
Use the IK goal to oriant the end joint.
Use the first joint to animate the rotation.

You have a non homocinetic and an homocinetic ( the second one keeps rotation velocity).

12-15-2004, 12:42 PM
Great stuff jeanphi :) it works like a charm !

12-15-2004, 02:30 PM
Thanks Weetos.
I like looking those mecanics running... It's magic...

12-15-2004, 04:20 PM
Wow, those don't just look great, they work great aswell!

Thanks jeanphi!

12-15-2004, 05:23 PM
c'est magnifique. le mécanisme marche tres bien. merci jeanphi. (you really should feel honored. it needs much till i try to write french :D )
That's exactly what i was looking for. :) :) :)

12-15-2004, 05:56 PM
Just for fun...