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  • Best Approach for Dynamics

    Posted by Joseph M. morgan on January 6, 2011 at 12:50 am

    I have what amounts to be a simple dynamics with gravity, and am wondering what is the best approach.

    Essentially, there are several coins that will fall into a chest. I suspect there will be a number of coins already within the chest.

    First, is it required that all objects under a solver be converted to editable? The coins may appear simple, but have quite a bit of detail, and I’m not perfectly secure in making them editable.

    Is there some way to use other, non-visible objects that I can then “parent” my coins to and have them under the solver? I don’t need absolute perfection, in the collisions, as long as the coins don’t flow through something.

    The same with the chest. The top of the chest closes at the end, it has a cloth restraining strap that falls into the chest, and I cannot make it editable. So, if I have to use an editable object, I’ll have to use some kind of proxy.

    So… am I thinking in the right direction?

    Brian Jones replied 13 years, 1 month ago 2 Members · 9 Replies
  • 9 Replies
  • Brian Jones

    January 6, 2011 at 2:01 am

    the quick answer is “you need R12” but it is possible in 10.5, just make the coin(s) you want to see children of an editable coin proxy(s) (preferably with many less polys, just the right size) and they will follow whatever they proxies do. Then make the proxy invisible (make the dots red) and force the ‘real’ coin to visible. Same goes for the chest but because the chest does not move (I assume) it does not need to be a child of the proxy chest it just needs to occupy the same space.

  • Joseph M. morgan

    January 6, 2011 at 3:27 am

    Hmmm R12… Maybe this project will bring in enough extra to pick up the upgrade…This is just a “pro-hobby” for me, though…. but I might want to get in while they still have an upgrade from 10.5. Looks like I need Studio if I want the features I currently have.

    So… it sounds easy enough, but the coin proxies won’t fall. I have the solver, the gravity, coin proxies, and the chest proxy under the solver, with the actual coins under their proxies. I used Newton gravity and a mass of 1 on the coins, 0 on the chest.

    I clicked Dynamics->Initialize all objects, and in the tiny little project I created to learn dynamics, this was all the magic I had to do.

    The only difference is in my real project is that I set the solver to start at the 60th frame and end at 120, though I’ll probably extend that and tweak the settings once I get farther into the project.

    What am I missing?

  • Brian Jones

    January 6, 2011 at 3:42 am

    it won’t be a problem with the Solver not starting until later… is the Rigid Body Dynamics tag attached to the proxy (not the coin)?

  • Joseph M. morgan

    January 6, 2011 at 4:15 am

    Yeah…. I changed the gravity type from Newton to Axial and for some reason it started working. Don’t know enough to know why.

    Now I have to solve another problem. The coins are vertically stacked and fall one after the other. Everything is fine until the first coin reaches the chest proxy. For now, that coin is bouncing like a ball (I’m sure I can tweak to fix it)… but when the first coin bounces, all the other coins bounce about as if they hit a surface as well.

    The coins aren’t close enough to one another to be bouncing off of each other, or, is one of the settings causing a spacial buffer around the coins like a force field?

  • Brian Jones

    January 6, 2011 at 4:36 am

    in the Solver/Details reduce the Collision EPS – it uses that to help prevent intersections but it sounds too large at the moment.

    reduce Elasticity in both the coins and the chest to limit the bounciness

  • Joseph M. morgan

    January 7, 2011 at 2:38 am

    Brian… I know you probably feel like you’re dealing with a first-grader… and with this, I am …

    The coins fall, passing in front of the camera. At this point, they are vertical along the Y. Then, they continue to fall down into the chest while the camera pans down. While the coins fall the flip horizontal along Z, so they land in the chest flat.

    However, the coins don’t flip. That is, they remain vertical along the Y, even though I keyframed the rotation of the coin proxy. Then, from time to time, after a while of clicking, and rendering the scene, they suddenly are flipped on their backs…

    It seems the more I get it working… the more strangeness that creeps in….

  • Brian Jones

    January 7, 2011 at 4:12 am

    have you read the Help – Modules/Dynamics/Keyframe Animation? The basics are
    – keyframes are ignored for an object that is under the influence of Dynamics excepting when the mass of an object is set to zero. (I don’t know if animating the Mass would be a solution but it might be)
    – A dynamics object can be attached to a keyframed object with springs “uniting” keyframing and Dynamics (I don’t see this but maybe I’m not thinking about it right)
    – you can bake the animation then modify it afterwards (but it does a keyframe for every frame of animation)

    Another possibility is to have an invisible collider that flips the coin for you – perhaps with animating the rotational mass and/or the angular aerodynamics it might be controlled but I don’t know. Perhaps you’ll find something better

  • Joseph M. morgan

    January 7, 2011 at 2:42 pm

    Yikes! OK. I see a couple of catch-22s here…. and I now realize my real problem started at the beginning, when I hadn’t planned on using dynamics at all.

    It is clear I should have started with simple proxies and dynamics, and then brought in the real objects, and retrofitting dynamics without proper planning is simply not the way to go.

    Brian, as always, you’ve been extremely helpful, but I think I’m going to cut my losses now and manually keyframe this relatively simple animation.

    Thanks again!

  • Brian Jones

    January 7, 2011 at 5:04 pm

    sounds like a good solution for the moment. For what it’s worth in 12 (Studio at least) you can mix keyframes and Dynamics so what you are trying would be possible in 12.

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