Hydraulics, but more than normal

[asciipig]

Hi all.

OK, forgive me as I'm a brand new XSI user, and come from a very long time using Maya. I am looking at moving to XSI sometime in the near future,and I'm using a small project to help me through.

And so I come to my first 'challenge'!

I can do a simple hydraulic ram, with one cylinder moving out ofanother. However, I need three sectios to my cylinder! I need to be able to grab a handle on the bottom of the leg, set a keyframe, and the move the object sat on top of the leg and have it follow that. The leg has to have three sections which can slide over each other like any hydraulic piston. And ideas?

Regards.

Larky.

[ritzbitz]

I'm not sure I fully understand your problem. But I'm about to post a zip file of a soft database that has a scene file called piston. I think it is what your talking about. It was done in XSI 3.01. Once I actually put it up on my site I'll post the link. But in the meantime I'll explain how to do it. I'm assuming you allready have the three parts of the piston built. So first you will need to get two implicit boxes for your controll points. Put one at one end of the piston and the other at the other end. Select the top controller (implicit cube) and apply a Direction constraint (Constraint>Direction) and select the bottom controller as the constraining object. Now Select the bottom controller and apply a direction constraint to it with the top controll cube as the constraining object. Now where ever you move either cube they will both allways point to each other. Now parrent the bottom part of the piston to the bottom controll cube and the top part to the top controll cube. You can now envlope the smaller part of the piston (the part that goies inside the other) to the two controll boxes. This way no matter how far apart you pull the controll cubes apart the piston never comes apart. I like to call it "The Impossable Piston". It may give you some problems if you have to texture map it but there are workarounds for that if necessary. Now for this middle piece. There is probably a better way to do this but I'll just tell you what I did. I constrained its position to one of the controll cubes and then the other. So it has two position constraints in its operator stack. Select one of the constraints (it doesent matter which one) and open its property menu. Then just use the blend weight slider at the top to get the desired effect. Last apply another directon constraint to the middle piece with either of the controll boxes as its constraining object. When you do this you may have to adjust the settings in the align axis section of the direction constraints property menu. Now If I understand your problem correctly that should do it. My server is still down but I will let you know when the example scene is up for download.

--eban--