[Blender 2.5] Which constraints to use?


i am working with blender 2.5 alpha 2 and I’m trying to animate a Crankshaft.
I’m using bones to animate the elements of the crankshaft. Basicly my question is: If I have two bones which are connected and parented, the one bone is rotating so the root of the other bone is following the tip of the rotating bone. Now I want the tip of the second bone to only move along one axis, while the other bone is rotating.

What kind of constraint do I have to use? I tried the “clamp to” constraint, but when I clamp the second bone to a curve which follows the z-axis, it doesn’t affect the bones.

How can I clamp the movement of the tip of a bone to a certain path or axis?

thanks a lot!


Track to will point the bone , Limit location …click on the other 2 axis and limit them so it will go freely on the first axis, Like for a piston?

Hm, that doesn’t work… I added a track to constraint, all right. But when I add a limit location constraint to the second bone and activate limits for the x and y axes, the second bone only points up, but the tip still moves away from the z-axis.

I created the attached blender file. If you move the little single bone, the two main bones will move according to the IK constraint.

Can someone do whatever is necessary to do to only let the tip of the second bone of the two main bones move along the z axis (up and down)?

Thanks a lot!


piston.blend (60.6 KB)

works for me

I found a old blend, hope it helps


cog11.blend (621 KB)

IK will do the job. I gave a rather convoluted explanation in this thread. If I were doing this again today I would extrude the bones the right way round to start with, rather than flipping everything partway through, but it should give you the general idea.

Best wishes,

I’ve looked at the files posted here, and none of them appear to really work, IMO. So I threw together a quick mesh & armature and recorded a quick video tutorial on how I rigged it. After I finished, I saw MCollett’s post, while I didn’t download the file, it looks to me like it works. I used a different method, but accomplished the same thing. I tried to post a thread in the tutorials section about my tutorial, but got a message that it needs mod approval.

So here’s the link to the video:

And the completed file is attached.

Hope this helps,


Crank1.blend (75.1 KB)

I haven’t watched your video, but in the .blend the piston motion isn’t quite right: when the rod is vertical the tip of the rod connects to the head of the piston as it should, but when it is at an angle the piston doesn’t come down far enough and there is a gap between them.

Best wishes,

Ah…Thanks MCollett!!! I hadn’t noticed that while creating the video, so I looked into things a bit… I rigged that last night night, recorded the video this morning and I accidentally used the wrong constraint on the rod bone. When I originally rigged the thing, I used a stretch to constraint for the rod bone, when I recorded the video, I used a track to constraint. Man, do I feel dumb:o…

I’ve corrected the .blend file with the correct one, removed the link to the video, and will be recording & updating the video and providing a link to the new video as soon as I can.

Nice catch dude!!

My apologies for my mistake,

‘Stretch to’ hides the problem better. But remember that real connecting rods don’t stretch ;).

Best wishes,

Shhh…don’t tell anyone :rolleyes:


nice and simple example.


in this set up - the “stretch to” bone doesn’t actually stretch