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A problem arises when I move the arm of a robot I am animating. A piston connected to (and a child of) this arm has a Damped Track on it. When the arm is moved using it's IK armature, the piston occasional glitches out of position, and then quickly realigns again as intended.

It seems there is some time needed to recalculate the right position. This would not be a problem for rendering a still image, but the glitching shows in 3D viewport movement and a rendered animation.

enter image description here

Exactly the same render of this particular animation yields a different result:

enter image description here

The arm is connected to a rotating platform (their bones are respectively child and parent). This platform has a child, a cylinder (recognizable by the two capsule shapes attached), that is also the target of the piston's Damped Track. I think this loop of constraints might be responsible, but i'm not sure how exactly. (And the cylinder also has Damped Track, with the piston as target; it also glitches, but not as often)

I also think my problem is similar to this one: Damped Track constraint on bone lags There may even be a proposed solution in the comments, but I'm not sure how to apply it to my situation.

The piston glitching or jittering is not intended or wanted. : )

I am interested in any solution to this problem, or any (other) reference to something that might help : )

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  • $\begingroup$ I ran your file and rendered it. Neither in my 3D View, nor in my render, did I see any of the issues you describe or show. Everything was normal. I was going to provide a video to prove it, but I can only post one in an answer. And I don't have an answer for you. Hopefully, though, this will give you an idea of what you might check next. $\endgroup$
    – R-800
    Jun 17 '20 at 3:17
  • $\begingroup$ Thank you : ) Your result is a bit unexpected though, and I'm afraid the opposite of helping me where to look next : ) Assuming you didn't change anything in the file, it would have to be something that is not the same for both of us. (might be my particular hardware setup; then I wouldn't know what to do) I think within Blender that only leaves Preferences. The only thing I can think of is maybe something to do with memory or cache, though I doubt it and also I have no experience with these settings. If there's anything you know about this or anything else you can think of, please let me know $\endgroup$ Jun 17 '20 at 11:57
  • $\begingroup$ I managed to fix it. Thanks again for helping R-800. (I'm still a little puzzled why you had a different render result, but i decided not to dwell on it) : ) $\endgroup$ Jun 17 '20 at 16:49
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A bit weird answering my own question but I found a solution. : )

I now believe the problem was due to the piston and cylinder being each-others Damped Track target. I suspect micro translations of their origins when moving caused it, but that is a guess.

I added an object, child of the platform, at the location of the cylinder origin. And also an object, child of the arm, at the location of the piston origin. I used those objects as targets for the Damped Track constrains, instead of the piston and cylinder objects themselves. It seems this has negated the glitching or jittering effect entirely.

enter image description here

Even though i found a satisfactory fix myself, still, thanks to anyone who gave this problem some thought. : )

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  • $\begingroup$ Glad you got it sorted. Also, there's nothing wrong with answering your own question. In fact, in this venue, it is actually encouaged, since it creates an opportunity for others with similar issues to discover your newfound knowledge. $\endgroup$
    – R-800
    Jun 18 '20 at 12:48

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