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Spline Dynamics/ Xpresso/ Object Collision
I’ve been looking around all day for good tutorials on how to make a balloon on a string. Actually, a bunch of balloons on a a bunch of strings.
I don’t really animate very often. I cobbled something together out of a number of different tutorials I found on other subjects. Something like this:
I made a string with Lathe NURBS. The spline has a Spline Dynamics tag and two Constraints, one on a fixed “ground” point and one attached roughly to the balloon.
The balloons are animated with an Xpresso tag which links their position to a plane with a wind-deformer on it. As the plane ripples, the balloons move slightly. So far, so good.
Here are my problems:
1) On the first frame, the points on the strings that are attached to balloons are off, and then they “snap” into place on the second frame. This makes the strings bounce around for a while. Is there a way to redraw the initial shape of the spline after the animation is set?
2) I don’t really understand how the up-vector on the target tag works. Actually, I don’t really know how the target tag works to begin with. I’m trying to make the point where the balloon is tied to the string stay pointed at the point where the string is anchored to the ground.
3)for some reason, all my balloons are beside the wind plane, not on top of it. It’s not a big problem, I just don’t know why that is.
and 4) I would love to be able to make the balloons able to collide so I don’t have to worry about objects overlapping.
I can certainly work around most of this, but if anyone can point me in the right direction with any of these issues, that would rock. That would rock hard.
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3 Replies
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Up vectors control the Axis of the object.
Targets control (limit) the Z axis.The fact that your plane is to the side does not matter at all. You can plug a constant with the point number into the point index input if you want them to actually be attached to the plane.
As for your collision I would make the all the balloons one object and then make them cloth and in the expert tab enable self collision. This way you can control the flex, wind, gravity from one place.
If you dont like that idea you could place a proxy balloon with a hair collider tag inside each balloon. Make the proxy the child of the balloon. This way you will get some overlap but not much. With this method you can use a bulge deformer for the flex. Just set it up with expresso to increase strength when it is X amount of units from the other balloons.
(I love these questions cause now I get to read what Brian says.)
/Randy
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First of all, thank you for the thorough answer.
I’m going to try your cloth idea, but when you say make the balloons into one object, can I just group them and put the cloth tag on that?
The second thing is that the problem with them being beside the plane is that they’re at an angle. They should be more or less straight up and down. I can’t seem to reposition the plane. don’t care if they’re attached to the plane so much as I would like to have an object that I can drag around to sort control the angle on which they’re tilted.
and lastly, the snapping thing… I wasn’t sure that I was clear on that, so here are frames one and two:
1) The strings are all straight up and down, and I can’t move any of the points on the strings (I can rotate the lathe NURBS the strings are inside of, but it seems like I should have more control than I do?)
2) The strings snap violently into place. -
No you can not group them. Select them and connect object. They do not need to touch each other or be bridged or anything like that.
The snapping thing is a Priority conflict. CInema is reading your Spline dynamics then your expresso. By selecting the tags (one at a time) you will see a priority option in the attributes manager. Since they are both defualt too zero Cinema reads the one highest up in the hierarchy. So make the Zero on Spline dynamics a One.
Spline dynamics will not let you move the points because its simulating. You need to control the movement with other means like wind or turbulence.
Also the Kinks you have in your strings are because you dont have enough subdivision. In point mode select all the points and right click choose subdivide… a small number will due.
And I thing you are using a Sweep Nurbs for the string and Lathe Nurbs for the Balloon.
/Randy
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