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# Joints & Mass

 Topics: User Forum Wiki Link: [discussion:18380]
 Skirvir Nov 27, 2007 at 2:37 PM First off, I'm new here, just joined the community in general because of this project, this is an outstanding project and I want to give serious thanks to Crashlander and anyone else who helped develop it and make it available to the world, keep up the awesome work. It took me awhile to get the project working (my own fault I'm pretty sure) at first but once I got it compiling and fired up the demo's I was very impressed, it looks and feels like professional quality. So, good job, and keep it up! My question, is about joints and mass, I know this is a physics simulator but I'd like to know how to turn off mass for an object. I noticed if I make the mass 0, it throws an exception, but is there a way to associate a body with another body via a joint (in my case I'm using a revolute joint), but not have that child object exert any force on the parent object? This may be outside the bounds of what the engine is all about but I guess I'm testing limitations and such. The reason I'm doing this is that I wanted to create a creature, which I've done, with googly eyes (which I've also done) however, the eye balls, exert force when they move around and make my critter move funny (though realistically as you'd expect a plastic ball with a roll of quarters in it to move, its just not the effect I'm going for) :) Is there any way to turn off this behavior or am I just using the engine in an un-intended way? Thanks! crashlander Nov 27, 2007 at 5:32 PM Edited Nov 27, 2007 at 5:33 PM Welcome, Skirvir. Glad you like the engine so far. There is no way to turn inertia for an object off. Bodies move by applying forces. You can't really apply a force to a body with out mass. Without forces, the engine doesn't know where to move the objects. A couple things you could try: 1. Give the eyes a fairly low mass compared to the body. This might lessen there affect. 2. Don't use the physics engine to move the eyes. Every loop just set the eyes relative to the body. Could be other options but these are what pop into my head.