# Rig crank mechanism

I am building a complex mechanism and a problem arose.

There are two bones, bone 2 copies the rotation of bone 1. If bone 2 is not connected to other bones, then it rotates in the same way as bone 1, but if bone 2 is connected to bone 5, then bone 2 moves slightly, not full.
like other bones inhibit bone 2

If you turn off Inverse Kinematics for bone 3, then bone 2 begins to rotate as expected.
How can I make bone 2 transmit full amplitude rotation to the next bones (5 and 3)?
mech.blend (1.2 MB)

I think there must be something unsaid here, and I don’t think I can explain what’s happening without seeing a file. First thing I’d suspect is that bone 3 has an IK chain set too long, to include and so rotate bone 2.

However, if you parent bone 2 to bone 1 instead of using a copy rotation constraint, it will acquire the full, appropriate rotation. (However, you might ask if you actually need bone 2, and whether you might just parent bone 5 directly to bone 1.)

Perhaps this example will be more convenient.
How to make it with bones?
It’s like a swing that doesn’t swing back and forth, but left and right.

3 parented to 2, parented to 1; 3 has a 2-bone-chain IK constraint. To swing, rotate 1. Presumably, just like what you have, although there needs to be an IK target for 3, not shown in your pic, at root level or parented to the same parent as 1.

i did it like this (see image below)
But the problem is that when I swing bone 2 left and right, it moves very very tightly, shuffles a very short distance.

Try it like I said. Chain length 2, bone 1 is the control. if you want to control it from the tail of 1, create a new bone at that location and give bone 1 a damped track targeting your new control bone.

it makes a mess of bones

I am sure that there are other ways to do this (I am not a rigging expert), but hear goes one.

Bone 2 copies rotation of bone 1 with bone constraint (OK)
Bone 5 (the bottom hoizontal one) should be child of bone 2. Turn off inherit rotation.
Flip bone 3 (bones pivot from their head). Add a damped track contraint to bone 3 and point to bone 5.
No need for IK constraint.
I do not know what you want to do with your bone 4 so I left it out.

Here is a file with the example, in case I did not explain properly. I changed the numbers in my file so that it is 1,2,3,4 instead of 1,2,5,3.
Bones.blend (744.1 KB)

Edit: sorry I mixed up the term head/tail, bones pivot on their head - THE FAT BIT! I have corrected it for anyone who reads this.

Thanks, it helped me
bandages thank you too