Cineversity

Hi CineFriends,
  I would like some insight concerning spline dynamics and hair constraints. I have a complex project which involves many dynamic hoses - part of a machine I’ve created. As I’m keyframing the motion, the ends of the hoses don’t move with the nulls that they’re constrained to. However, when I click “Play”, it all works perfectly - the hoses move and remain attached.
  Here’s a simpler way of explaining this via a very basic example: A rope (consisting of a multiple point spline) has hair tag constraints applied which attach the end points to nulls. Hair spline dynamics are applied. This is simple and all works fine. When one of the nulls is keyframed to move toward the other, it plays back perfectly. However, if the null is manually moved with the mouse, the constrained spline end does not move with it.
  So here’s my question: When in the stage of creating the animation (keyframing), shouldn’t hair constraints keep a spline attached to a null?  I thought that it should….  such as when working with IK and dragging the Goal around and watching the joint structure follow.
Is there a way to do this? I suspect that I may be missing a simple step. I also tried this us Xpresso, with the same result.

Thanks for Your Insight,
Larry

Hey Larry,

Is your question based on a tutorial (as you are in the tutorial Forum)?

If so please let me know the name so I can follow.

If your question is purely based on your private project, would you mind to continue this discussion in the Main forum and share a simple set up as well share with us which release do you use.

——-

What I got so far, you have a null as constrain to a spline, and the spline is dynamically. If I got this right, and you like to move the Null object while the animation is stopped, nothing will happen, as the dynamic is not calculated while the timeline is stopped. Otherwise your scene might explode from time to time.
Dynamic is highly dependent on influence over time. Influence with no time, is like infinite acceleration. Like driving 100Miles per “zero” hour, impossible in this reality ;o)

Please let us know, I’m happy to move the thread, so you don’t have to start over, if you like.

All the best

Sassi

Hi Dr. Sassi,
  WHOOPS! I had completely intended to post this in the Cinema 4D Q&A Forum - I accidentally clicked on the Tutorial forum. Sorry!
  Yes, your understanding of my question is correct. Your explanation of ‘infinite acceleration’ makes sense. I was hoping that I could work with hair dynamics & constraints similarly to the way we use IK when the timeline is stopped: by moving the ‘Goal’... and the bone structure responds. It seems like I’ve seen tutorials where this was done…
  I just tried to attach a simple “.C4d” file to provide you with an example, and received an error message “the filetype you are attempting to upload is not allowed”. I’ve attached C4D files at Cineversity in the past… any tips on what I’m overlooking?

  Thank-you!
  Larry

Hey Larry,

Any attached file should work, as long as it is zipped (compressed) and does not exceed the max file size. C4D files “natively” won’t work.

The only way to keep the dynamics natural, but having the option to move things, is after you have used the cache option in the Spline Dynamic. YOu need then a Null object as parent to your spline. However, this movement will not affect the dynamic anymore. I’m certain that is not what you like, but I had to mention it.

The more I would know what your initial target is, the more I might find a solution. With initial I have really the origin in mind, as I have seen over the years that partly solved problems obscure the view to the “real” solution.

A reason why I ask for the file and the target as well.

All the best

Sassi

Hi Dr. Sassi,
  I attached a .zip file containing a very simple C4D example of my question. Also contained in the zip file is a rendered still .jpg of the my more complex project. If you examine it, you will see cables attached to the legs, which will swing freely as the ‘robot bug’ walks. My hope was that these cables would remain attached as I keyframe the animation.
  If there’s not a way to resolve this, it’s not an obstacle to the completion of the project. It would just be a cleaner way to work.

  Thanks for your input!
  Larry

Hi Larry,

Frame zero is the initial frame, where the dynamics will be set. IF you like to make changes at that point, you need to move you “Null L” and then the Spline point to the new “Null L” Position.

Experiment: Set you “Null L” on an Layer, and switch the animation for that layer to off (the filmstrip icon). Start the play button and move your “Null L’, the spline follows. If you move the “Null L” now to a different place than it was on frame zero, you might notice that it jumps: Initial Frame. /experiment

If you move the “Null L” at any other frame time and set a keyframe for the null, the spline will follow. Which indicates again, Frame zero is a special case. Why is that? I f you follow the forum for a while you might have seen the question that some dynamics problem are based on the fact that objects where left on the position of the last frame while the application starts over on frame zero. Not nice (but interesting) So frame one needed for this objects a keyframe or any kind of set-back-to original state option. That is the complete problem here.

I hope that makes sense

All the best

Sassi

Hi Dr. Sassi,
  Yes, I was aware of the need to restart from frame zero for the dynamics to execute properly. But it was helpful information and I appreciate it. Your comments about dynamics and infinite acceleration were especially applicable.
  My project is progressing well and I just wanted to send you a quick note to thank you for your insights. Your personal assistance on Cineversity is greatly appreciated!

  Warm Regards,
  Larry

Hey Larry,

Thanks for the feedback. You wrote that you were aware of the zero frame handling. Sorry, I did not think for a moment that you know it or not. When I write here something, it is mostly based on three reasons. To solve what is in question. But more importantly I write in a forum, which means I have to write most of the time more, more than the one who asked need in that case, to support people at the same time who are new to that theme.

On the other hand, I have to make certain that we have the same idea about the subject. Which will say, I might have gotten the wrong idea about. To share “my” details” helps identify these problem areas, vice versa.

Having said all of that, what ever I write here is not intended to describe my impression or what I think someone knows or not. I never underestimate anyone here. I also do not inter- nor extrapolate from the question itself, to gain with such a wrong idea about the one who ask. We talk about tools here, an option to create your targets. In your create is the largest potential, and that is beyond this forum to judge.

However, that was maybe not your point, but it gave me the option to talk about, forums wise. Thanks. I’m happy when things work and everyone can go back to focus on the fun stuff, to realize what was the initial idea of a project. I assume first that anyone here is an artist or has the potential to be one. I try only to support, so people get not stuck in tool problems. We need the tools and they are great, but they should not be in our way. :o)

Thanks again—very nice feedback. Makes my day. ;o)
Have a great weekend

Sassi