Upvector inverting bones? (post disappeared)

[atyss]

Hi there, sorry if this sounds d

[fredc]

Perhaps it would help to imagine that the upvector is defining a plane for the skeleton to reside in. The upvector controls the entire skeleton, from ground to effector, not just the bone you attach it to.

If you look at your own arm, if you flex your bicep, it is equivalent to moving an effector and all of the motion is happening in one plane. However, if you roll you elbow in or out the motion is effecting the plane that your entire arm resides in...which is like moving the upvector.

Hope this helps,
Urp

[atyss]

Thanks Urp for you input.

However, I don't see how it does apply to my problem. Maybe I'm missing something very obvious here.

Are you saying that it does not matter if I have to place my upvector and animate it in a negative way, as long as it make it move on the desired plane?

Merci - Thanks
Bernard Lebel

[fredc]

Yes. The postion of the upvector is not important. The motion it gives to the skeleton is all that matters. All the upvector is doing is controlling the rotation of the imaginary plane the skeleton resides in.

However, lets do a test to be sure we are talking about the same thing.

1. Place a two bone skeleton in the Front view.
2. Place a null on the inside of the bend.
3. Select the first bone of the skeleton and select Skeleton/UpvectorCns, then select the null as the reference object.
4. Select the null in the top view and move it up and down in the Z direction.

The skeleton should rotate around the red line connecting the base and effector. The two dotted lines connecting the skeleton to the null should define the plane the skeleton resides in.

Is this behavior happening for you?
If it is, are you having some sort of other problem. Perhaps I am misunderstanding your problem. If so, can you post instructions on how to reproduce your problem?

Thanks,
Urp

[atyss]

Ok I Urp I did what you said. It happened exactly as you said.

So I will provide more details.
In my scene, I have a 2-bone leg. The knee faces the front view. It folds correctly, meaing that when I move the leg's effector, the knee bends towards the front view (Z positve).

Now I place the null that will serve as upvector in front of the knee (still in Z positive). I apply the constraint, and woops! the knee now points to the back! (Z negative). See below.
The red null on the left side is the upvector.

You see? If I place the null in the back, the leg stays in its orientation, but the effect of the null is inverted. So it is the same plane, it's just annoying to have to animate the null in an inverted fashion.

When I did your test, in fact I did 2 tests. One with the null behind (like you said), and one with the null in front. Both reacted the same way: the joint always faced the null (by facing I mean bending towards the null). So what is happening in my case?

Thanks - Merci
Bernard

[fredc]

Atyss,
I assume in you scene that if you put the null behind the character, then the knee flips to the correct direction. If that is the case, it looks like everything is working normally.

For skeletons the upvector is always to the inside of the bend. As long as it is consistant I wouldn't worry about it. I prefer the nulls be behind on the legs anway. It keeps them out of the way.

Urp

[atyss]

Ok then, thanks a lot!

It's the first time that I have to put the upvector inside the bend, so I was confused. But if you say that it's normal, well it's fine with me!

Thanks
Salutations - Cheers
Bernard

[ian-shep]

You have already have got a solution, but if u decide you want to have the up-vector infront. Place the up-vector on the top bone, the bone will flip, but select the bottom bone and change the Z value to a negative. This way the leg will bend right and the vector will be infront