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Constant distance using Xpresso
I am no Xpresso expert, and I don’t know if this can be done, but here goes:
I’ve made a cable, using a Sweep object, and the path spline has a number of points along it to which I’ve attached objects, using nulls and Xpresso, so that if I move one of the objects the spline (or cable object it’s attached to) moves with it. There are about 12 objects attached along this cable. Now what I want to do is move the end object along a curve, and have the others follow it, keeping the same distance from each other, without “stretching” the cable. I can do this painstakingly by hand, moving each object at intervals, and trying to keep things even. But I thought maybe this could be done using Distance nodes in Xpresso to calculate the distances between the objects. But then what do I output the results to that will actually keep the distances constant? This is where my tiny brain fails me. Does anybody have any ideas about this?
thanks,
Jack -
6 Replies
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The cable stays straight between the ends?
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No, it has to curve. It represents a mooring cable with oceanographic instruments attached along it’s length. There are floats as well. It lies floating on the surface of the water, and then a weight at the end is dropped, pulling the whole line plus instruments down. But they go down following a sort of curve, straightening out as the whole thing is submerged.
Jack
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Doesn’t a distance node just output a distance?
You could have all the objects follow one object at a fixed distance / position by using global position data and a math: add node in vector mode for each follower. You’d have to set up each individual object first, getting the distances from your “leader” as vector data … though it might look a bit mechanical.
Anyway this set-up might do it – set the math node data type to vector, the constant to add to vector, and fill in the x y z offsets.
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if you have Dynamics it can be done like this, assuming it’s somewhat like what you are after.
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Mike,
I’ll play with this a bit and see if I can understand how it works (Xpresso is like Greek to me, except for a few simple things that I’ve learned to do with it). Thanks.
Brian,
This looks very much like what I want to do, with the addition of having the whole thing move downward as it curves down and then straightens out. I think this might work. Now I have to learn dynamics! I’ll give it a go over the weekend and see what I can do.
thanks,
Jack
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Brian, I’ve given this a go using my mooring cable and attached objects, and it works. Thank you for your help on this. I read through the Dynamics docs and went through a tutorial I found online, and then I took a look at your file and applied it to mine.
First I copied my object into a new file and then put Dynamics to it, with the idea in mind of getting it to work, and then copying it back into my animation file. But I found that although I could copy it into my file, dynamics and all, it ended up in a different position and orientation to where I want it to be. When I tried to move it, and rotate it to position it where I want it to be, everything went haywire. Is there a way to take the whole thing with Dynamics applied and reposition it, or do I have to build it in place? I put everything into a null object, and tried rotating that, but it didn’t help at all.
Jack
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