Bones stretch my model strangely

(Pörzi) #1


I searched this problem but I didn’t find an answer for it.

I tried to make a human model… the legs are working just fine but the hands aren’t. This image will probably explain the problem:
The hands stretch in a strange way. The armpit is another problem. If I rotate the hand 90 degrees it will become very thin.

Any help would be appreciated!


(Duoas) #2

What it looks like to me is you are scaling parts of your model non-uniformly.

This is hard to explain without pictures. Imagine a perfectly round clock face with the minute hand at 15 minutes. Let’s say the minute hand is 10 cm long. If you rotate the hand to 30 minutes it will still be 10 cm long.

Now imagine you magically squash the clock so that it is half as high as it was, but the same width as before. With the minute hand at 15 min it is still 10 cm long. However, the closer you rotate it to 30 min the more it will ‘squash’ down to 5 cm long.

The same thing happens inside an armature. When you ‘squash’ (or non-uniformly scale) a parent bone in one dimension, that scale affects all child bones the same way.

There are several ways to fix this. The simplest is to toggle the “Hinge” button in the Armature Bones panel of the Edit buttons while in Pose mode. If you still need the bone to follow the parent’s rotation you can use a copy rotation constraint.

Hope this helps.


(Pörzi) #3

Thank you for explaining the problem for me!

Unfortunately the hinge button doesn’t seem to correct the problem. And I can’t get the Copy Rotation -constrain to work in any way. The bones just keep their original angle.

But the most important thing for me right now would be to get the bones working the way I want them to work. (no stretching)

Here is another image showing the problem


(patdog) #4

Tab into edit mode and move the root of your shoulder bone further into the body [marked as a green dot in your illustration] Try move again in pose mode and note the difference. There is always going to be some deforming - usually this is compensated by adding Shape Keys using the bone as a driver…

Look here for tips…


(Pörzi) #5

Thanks! I think I can get the armpit problem solved now… but still the bone grows in length when I rotate it and it doesn’t look good. It also makes the fingers too long etc.


(Duoas) #6

It is definitely some sort of scaling problem. Have you scaled the armature as a whole? Or some parent, grandparent, etc. bone of the arm?

If you can’t find it, post the blend (or pm me) and I’ll fix it for you.


(Pörzi) #7

I didn’t know you shouldn’t scale the armature. :o

I’ll try to do the whole “sceleton” again. Hopefully that helps. Thank you!

PS: I really appreciate that you offered to fix the armature for me!

Edit: I tried to scale the whole armature in the opposite direction… it helped. Now I just have to resize the bones in another way. (so that the model is scaled as I want it) Thanks again, everyone!


(Duoas) #8

There’s nothing wrong with scaling the armature. In fact, the ability to scale the armature object as a whole is very useful when combining models into a single scene.

The problem comes when you scale one axis differently from another, you get the “clock” problem I used as an analogy above. If you ever watch Futurama, there’s an episode where the professor invents a box leading to a parallel universe. In the end each universe swaps their boxes so that they have a box containing their own universe. And the last part shows Fry sitting on the box and squashing it a bit, which causes everything to squash a bit. (Sorry I don’t have a picture for you. Either you’ve seen the episode or not.)

Glad I could be of some help.


(bob-blender) #9

Your post give me this idea ( Mysterious Clock).



(Duoas) #10


All you need is to attach a little round circle to the end of the hand that doesn’t scale as it spins around and the weirdness will be perfect!