bones that have a target bone shake subtly

[Daxel]

So I noticed today that my rig had some points shaking very subtly when there was absolutely no animation, and at the end I discovered the the problem was that the forearm bones had target bones and if I zoom on the tip of these forearm bones I can see how they are constantly and randomly rotating a little bit each frame. If I remove the targets the problem is solved. It is so subtle that I wondered if this could be the normal behaviour of bones with targets but no, I quickly created the same bone rig again and the bones were always precisely pointing at their targets with no movement at all.

So tomorrow I will keep investigating the problem but I wanted to share it in case someone knows what is happening.

[Greenlaw]

Sounds weird. I don't think I've noticed that here but will check it out in a minute.

FWIW, I don't normally use Target bones for arms unless I need to pin the hands to something, like to the hips or on a table. Any other time, I key them untargeted and use FK only (Alt+Manipulate Bones.)

Do post an example, though.

[Greenlaw]

Yeah, definitely post an example file.

I made a basic Bone target setup with some animation and long holds, and then tried some settings variables, but not seeing any shaking at all.

[Greenlaw]

Just a thought: Could it be that more than one bone in the chain is targeting the bone?

I just tested that and didn't see any shaking, but I wonder if it might in a specific setup or circumstance.

[synthsin75]

Sounds like Moho might not know which way to rotate the bone chain to reach the target.

If that's the case, you might be able to add a bone rotation keyframe on frame one to tell it.

But just a guess without seeing an example.

[Daxel]

Thanks for chiming in guys.
I was preparing the minimal reproduction project but didn't remember my dropbox pasword and ended up discovering that it is actually just how targets work. It is very easy to reproduce, basically it always happens. It's just hard to notice because you need to:

1. Hold the pose for a period of time. Freezing points on frame 24 will do the trick.
2. Zoom in quite a lot on the tip of the bone that is in contact with the target.

The more bones you have on chain with IK activated before reaching the target, the more the bones seem to shake.
In practice, you will have to zoom sooo much to see the tip of the bone shaking when you have only a two bones chain, while with a three bones chain you can see it with half of that zoom (still a lot of zoom). My chain had 5 bones with IK and I could see the bones shaking very subtly without even making zoom. The art shaked subtly too on the workspace, and I could see the vector points moving. If you select them, you can see they change their X and Y positions. However, even on this 5 bones chain rig, the shaking was not noticeable on render at normal distance. Zooming in until only two bones were visible on camera (so, lets say, a one arm closeup), made the shaking noticeable on render, even if very subtly.

My conclussion: the relevance of this is low. You need either a very long zoom or a long chain of bones hoding position with a still camera for it to be subtly noticeable on render. If you face exactly that situation, you can just hold position without using targets and then activate them again. But the subtle shaking may even not bother you (it is common in FBF after all). If it is an easy to solve bug, then it would be nice to have it solved I guess, but if it's a performance limitation or optimization then it may not be worth it to change it.

[Greenlaw]

Ah, now I see it! Yeah, I had to create multiple bones in the chain (I have about 5, with the targeting bone second from last) and made two identical Freeze keyframes about 24 frames apart. When I zoom in tightly, the shaking is quite noticeable.

I think this is because I have the bones in a zig-zagging pattern, and Moho may be experiencing IK conflicts like Wes suggested. Also, if I delete the keyframes on the bones and leave only the target bone's keyframes, the shaking goes away, so maybe it's also a bit of what I described earlier.

Granted, the rig I created for this test is garbage and not something I would normally use, but I can see how this could possibly be a problem in a real-world situation. From what I'm observing right now, I need to zoom in insanely close to see the shaking. I wondered if this was just a navigation/display issue, but when I zoom in properly with the camera, I can still see the shaking.

I wonder if complex IK with a bone target has always done this. FWIW, I've never noticed this when using Moho in everyday TV production, and I don't think the shaking is strong enough to be an issue under normal circumstances. But now that I'm aware of it, I'll keep an eye on it.

[Daxel]

I think this is because I have the bones in a zig-zagging pattern, and Moho may be experiencing IK conflicts like Wes suggested. Also, if I delete the keyframes on the bones and leave only the target bone's keyframes, the shaking goes away, so maybe it's also a bit of what I described earlier.

I tested that creating strictly lineal chains and it still produces shaking even with just two bones lineal chains. Also tested making keyframes only for the target bones with Freeze Selected, and the shaking keeps happening here, so maybe you didn't zoom enough.

Yeah in practice it doesn't seem very relevant, but I added it to my notes just in case I'm using a script or technique in the future that expects the bones or the points to have the exact same properties or something like that and this ends up being problematic.

I'm also curious to know if this happened on M12.5, but I don't have it installed.

[Greenlaw]

It occurs in Moho 12.5 too.

Well, considering the amount of broadcast/streaming TV work I've done using Moho since 2015 and nobody I work with ever noticing it as a problem, I'm not going to sweat it.

[Daxel]

Thanks for testing. Yeah in practice it's very hard to have a problem with it.