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  • Create Cuff parallel constraint when rotating hand.

I've been puzzled by this.
It feels like it should be simple... but I cannot work it out. 🤔

I want to create a bone that basically acts like a piston up and down the Y axis of the arm.
So that when I rotate the Hand, it moves the "piston" cuff bone up and down the length of the arm.

Basically I want a local rotation to translation constraint... I think?

Kind of like the crank shaft example in the forum, but able to be relative, so I can animate the arm moving around.

This post seeeeems to have what I need but it's lost it's files
https://esotericsoftware.com/forum/d/15002-crank-slider-rig

Any ideas I will be so grateful!!

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To achieve the effect you're looking for, where rotating the hand moves a "piston" cuff bone up and down the arm, you can use a combination of transform constraints and possibly IK constraints. Here's a general approach:

  1. Transform Constraint: Use a transform constraint to link the rotation of the hand bone to the translation of the cuff bone. You can set the constraint to affect only the Y-axis translation of the cuff bone. This way, when the hand rotates, the cuff bone will move up and down along the arm.

  2. IK Constraint: If you want the cuff to maintain a specific orientation or follow a path, you might consider using an IK constraint to control its movement more precisely.

  3. Relative Movement: Ensure that the transform constraint is set to relative, so that the movement of the cuff bone is relative to the arm's position, allowing for animation of the arm moving around.

The crank-slider rig example you mentioned involves using a transform constraint to mimic the translation of a rotating bone, which is similar to what you need. You can adapt this method by ensuring the constraint is set to affect only the desired axis and is relative to the arm's movement.

If you need more specific guidance, you might want to experiment with these constraints in a simple setup to see how they interact and adjust the settings to fit your animation needs.

ArtizensAnimator I've created an example of a rig that I think could probably accomplish it, could you check it out?:

cuff-example.spine
864B

The animation inside looks like the following:

Changing the position of the star bone causes the red bone to move towards its tip. By changing the position of the star bone, you can adjust how far the red bone moves.

If the sleeve length shrinks as the cuff lifts, I think you need to use the IK constraint, otherwise I don't think you need it.

      Misaki This is wonderful thankyou so much for your reply 😁...... however, it doesn't quite work becuase as soon as I animate the arm, the cuff bone moves.

      I can't seem to find any way of making it relative to the Arm bone... so that I can animate it without the Cuff bone sliding about the place 😃

      I've tried many configurations of IK constraints, but none of them seem to produce a straight line of motion for the cuff bone...?

      I've noticed that there is a pending issue in the Github for the spine editor to do "driven key" stuff...
      EsotericSoftware/spine-editor121

      Is that something that's in the pipeline?
      Do you have any other ideas? I feel like I'm missing something
      🤣

          ArtizensAnimator Ah, sorry I didn't take that into account properly. I'll see if I can resolve this.

          I've noticed that there is a pending issue in the Github for the spine editor to do "driven key" stuff...
          EsotericSoftware/spine-editor121
          Is that something that's in the pipeline?

          Yes, we cannot give a definite answer as to when it will be implemented, but we understand that this is a much requested improvement and is one of the issues we hope to address as soon as possible.

            ArtizensAnimator I've been thinking about this for a while and can't think of a way to make it work automatically when the parent bone rotates. As for translation, the following setup seems to work fine:

            cuff-example2.spine
            882B

            I think SilverStraw's solution is good if you don't mind the sleeve being compressed, but if you don't and you want the bones to move, it may be difficult to achieve that automatically.

                SilverStraw

                Misaki

                Thankyou both so much!
                Silverstraw's solution works great! 😁😁😁 🙌🍾🥂🎉

                tThe thing I was missing was ordering the influence of the constraints correctly!!

                Thankyou again! 🙏