Constraint tag for rokoko slipping feet (hands)

[chemical-subject]

Hi,

I’ve tried following this tutorial:
https://www.youtube.com/watch?v=IRuKDZweTss

to “lock” a hand to the surface of a table but no matter where I position the “constraint null” in the joint hierarchy of the reference mocap the rest of the limbs keep warping away from the “constrained” hand. Is there a really obvious way to solve this that I’m overlooking?

Thank you for any advice you can offer.

[Dr. Sassi]

Hi chemical-subject,

The image can have only 500 pixels vertically.

To use the Character Definition, one must understand that almost all motion transfers are based only on rotation. This seems to be excluded information in this video.

The key is to transfer the motion size-independently. If the position were included for each Joint, the target character would often "crumble".

The best way is to have the T-Poses as closely orientated as possible so all rotations are transferred with the greatest option to match.
That has been ignored in the video, and the resulting rotations created unwanted motions.

There is no one-size-fits-all fix for that, but to constrain something only with a position of one Joint-tip is questionable, as it might stretch the Joint.

.
If you would like to fix something like that while using the origin position of parts of the joints, I would set up an IK solution for the two joints that define the motion, so the stretch is not forced, and the motion stays hopefully in a believable range. Again, there is no one-size-fits-all solution. This is a fix of a symptom, not of a source.

I have two files below; one showcases the problem when the T-Pose was ignored to set up properly, and the second file uses an IK setup to have the end of the joining chain meeting the same position without introducing stretched elements.

CV4_2025_drs_25_CAsl_01.c4d

CV4_2025_drs_25_CAsl_02.c4d

The Goal, can be a child of the Table, in your example, or just positioned there. (I do not have your file nor the image)

Enjoy your weekend

[chemical-subject]

@Dr-Sassi Hi,

Thanks so much for getting back to me on this, I really appreciate it. I've tried to follow your instructions, though I'm fairly certain I've followed them incorrectly as I don’t understand the rational or function behind each step of the process, particularly the role of the pole vector and where each of the nulls should be positioned in the joint hierarchy if the hand is the bone I am trying to impact.

I’ve tried watching some of your tutorials on IK tags but to no avail. I can’t attach the file itself as it’s too large but I’ve attached an image of the setup.