# IK stretching. The meaning of the numbers...

Could somebody tell me what the Stretch number in IK is linked to?

I am trying to make a bones of a certain size stretch to another size. And I need to know what the number under Stretch does…

If I make a bone of lenght = 10 and apply stretch=1 it gives a maximum stretch to length=324 (so the relationship is not a simple length*stretch)

A stretch=0.5 gives a maximum stretch to length=230

A stretch=0.1 gives a maximum stretch to lenth=110

Doesn’t seems to be a linear relationship…(if it was, at stretch = 0.5 it would allow a length like 162 (324/2) and stretch = 0.5 would allow lenght to go to 100)

I am puzzled because I don’t know what stretch refers to…

If someone know, thanks for reading

If I have no answer here, I will try my luck by asking at the source (blender.org :))

I don’t know how to explain it mathematically but that ‘stretch’ number is related to the ‘Scale’ numbers for the coordinates in the N tab. Roughly speaking, if your N-tab numbers are all 0.20 and your Stretch number is also 0.20 the bone will stretch about 1 BU. Changing either to 0.40 (while leaving the other at 0.20) will allow it to stretch 2 BU.

%<

mmmmh more and more puzzling…

So I spawn a bone whose base is 0,0,0 and tip is 1,0,0… and an effector roughly the same size (base 1,0,0 and tip 2,0,0)

In the N tab, I put xyz scale to 0.2
ScaleX:0.200
ScaleY:0.200
ScaleZ:0.200

I end up with a mini bone
Okay… now I put Stretch to 0.2 and the bone seems to get back to normal (0.99 but okay…). Moving the effector make it stretch further to 4.20

So. Let’s put Stretch to 0.4 and now the bone can stretch furter to 8.20

And here I was thinking it would be piece of cake…

all I wanted to do was to make a bone of length 1 that could stretch to 1.5 #whimper#

Well, guess I will have to find another mean to achieve that

In the next release (or any build of cvs), if you’re not using a bone in an ik chain, you can restrict the scale to certain ranges (per axis).

Aligorith

`````` In the next release (or any build of cvs), if you're not using a bone in an ik chain, you can restrict the scale to certain ranges (per axis).
``````

If I am not in a IK chain?

Well I kind of hoped to use it to do some bulging business… But I can replace it with other constraint no sweat…

Or maybe it’s time I try Orinoco’s tutorial…