Cineversity

I want to animate a rotating object that starts off slowly and reaches its maximum velocity and keeps rotating for an extended period of time.  My setup is 2 Null objects controlling a third object. The first Null object is the control object that slowly accelerates both objects and the second Null object is the control object for repeating the constant speed. How can I seamlessly match the rotational speed of the two Null objects or is my setup incorrect?

Thank you

Hi marcpurcell,

My first question would address of course the requirement of the two Null Objects: Would it be doable with one as well.

However, I guess you have a reason for this.

How about this, which seems to be the simplest set up.

Create the Null Rig, Parent/Child

Animate the Child with a repetition after the initial Key Frames. Time Line (F-Curve Mode), Function>Track After>Continue After. Start from the first frame.

Set up two keyframes for the parent shorter than the initial acceleration time, but lose. Do this in the opposite way, so the rotating object would stand still.
Go To Timeline (F-Curve Mode), F-Curve> Make Snapshot> Create Snapshot 1 (then Show Snapshot one. This helps to guide you, on one side of the snapshot it will be too fast and slower on the other side. See example.

From there you have to pull the last keyframe to the left and adjust the Handle so it is horizontal.

This might be counterintuitive first, but perhaps the easiest way—as you work only with one keyframe, and not try to sync two.

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Animation is the change over time, and with that being said, the degree [º] from one frame to the next is all there is for a one axis rotation. This needs to be matched, if one stops and another takes over. BUT the key is to have keep these areas with the same interpolation. Ease in and ease out will mostlikely not overlap perfectly for the wanted equilibrium.

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My suggestion would be based on one Null Object (the blue one in the example) and there to use just the Continue After. As in the example above, the step-ness of the curve shows the rotation-speed. In the image you see an example that the “bow” of the acceleration is below the straight line. If the bow is above the line - it would start out too fast and lower than. Just adjust the handle of the second keyframe and you see the results.

Let me know if you like to share more about your target, and perhaps we find something else…

All the best

Thank you very much. The second (blue example) is a great solution. A small follow up question. I’m recording two keyframes 1) with a 0 rotation value, and 2)the second with a value for P. The Continue After command only seems to work if I set the Before field to Off. Am I doing something wrong? Also, I don’t see the tangent line as I do in your example.

Thank you again

You’re welcome, marcpurcell!

Please check the attached file, I tried to reproduce your observation, but I can’t. Perhaps you share your file, just the Null object in question. I will have a look into it.

You might be aware already about this, but just let me make certain that this information is given, if you click on the, e.g., rotation - track, you might have some options that you need.

The handles are available if the previous key was set to Spline Interpolation. Check as well how much you can do with the (Key selected) Attribute Manager>Left/Right—Time/Value (four parameters).

My best wishes

P.S.: If you like to have an alternative, perhaps XPresso based, here is a sketch. I call it a sketch, as “scrubbing” with the timeline back and fore will “screw” up the rotation. So, be aware of that. However, in normal play-mode or during rendering—it is stable!

Just an idea :o)

Blue
Makes certain that the first frame is switched to the value “Start-RHº”

Green
As in the editor view, content is updated more often, this set up creates a switch to avoid additional updates for each “refresh”. Note, if you go back with the time slider, and then forward again, the absolute rotation is not equal to the one during the rendering!

Yellow
The set up to ask the current rotation and adds the “Add_Per_Frame” to it.

Orange
The User Data “Start-RHº” is fed in here.
. .

Check the XGroup for the processing sequence

Enjoy

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Thank you for the support and help. Both are great solutions.

Very nice of, marcpurcell! (I hope this is the way you like to have it written, no capitals)

Your question made me thinking if I should consider a series about F-Curve animations. It is certainly something I would like for everyone to have, and to use like as easy as to scribble with a pencil!

Have a wonderful Sunday!

:o)