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[Familyman]

he is what I have, A large tank style cannon.
He is what I want it to do, when firing I want it two sharfts of the cannon to recoil into each other.
I have tried palying around with bones and angels but can not get the affect I want,
So is there a way to shorten and lengthen bones during animation, I have tried to editing a sequence starting with a bode long and making that a keyframe and then 20 frames later changing the length of the boneand making that a keyframe but that doesn't work.

[Kubajzz]

It's not possible to change the bones length during animation.

However, there is an easy way to create telescopic movements. You said you had tried playing with bones and angles and you wasn't succesful... Try this tutorial, it should work:
http://www.geocities.com/lanceart/article02.html

I would also try morph targets, it should work perfectly for a movement like this...

[Familyman]

I think I just figured it out, but I will check the tutorial maybe try morhing, thanks.

[RudySchneider]

Familyman ---
WHY are you using bones for animating this?  I suppose there may be something to be gained from using bone weights to alter the actual shapes of the barrel sections in a cartoony way, but there's no need for bones at all, from what I can tell.

You've got two sections of the barrel that actually move --- the middle section and the muzzle section.  Simply parent the middle section to the base section, and parent the muzzle section to the middle section.  This way, the middle and muzzle sections will "track" any motion the base and/or middle sections make, respectively.  Then, since it's primarily linear (rather than rotational) motion you need, you can keyframe along the appropriate (X-, Y-, or Z-) axis for the middle and/or muzzle sections.

I rarely, if EVER, use bones for any of the animations I've created (which, if you're interested, you can se at www.rudyschneider.com).  Bones are primarily meant for objects with organic qualities, where the object surfaces must change shape --- such as the folding and/or twisting of skin when a character moves its head up and down, and left and right.  As Kubajzz, pointed out, another way to do this is with morph targets.  The only possible down-side I can think of for your application would be controlling the "tracking" of the morphs.

By the way, guns (or cannons) don't actually recoil in this fashion.  In general, the entire length of the barrel, through which the projectile travels, cannot change in shape between the firing chamber and the muzzle.  Instead, the barrel is usually suspended on a sliding mechanism fitted with springs and/or hydraulic shocks, which absorb a portion of the energy from the projectile as it accelerates through the barrel.

[Familyman]

coming from a military family you don't need to tell me how a Gun or Cannon recoils, but thanks.
As for the whole parent tracking thing, that is a very interesting method, I might try it, thanks for the idea.
And the animation I am working on isn't meant to be real, just look good.
 

[RudySchneider]

Here's a quick GIF animation I threw together to illustrate my point.  It's a bit slow, but that's what I get for FREE AVI-to-GIF conversion software...

[mcheccyb]

use www.zamzar.com to convert your files. no programs involved, completely free.

[Olias]

Yes, I would definately go the route RudySchneider pointed out for this animation.  Even if you could get the bones to animate, it's so much easier with the parenting and movement keys.