Hi all! I've been working with the vellum muscle nodes for a few weeks now and I'm still having issues getting good results. I'm starting with a simplified model of the Emil muscles and skel that ship with the unreal ML deformer demo. The Vellum Muscle setup is my own using that file and the dino legs file as a reference. I'll attach my hip file here I have just the pectoral setup running into the MuscleSoverVellum node for now.

My muscles solve like kids slime lol. I try to adjust the Muscle Properties>Shape Stiffness but it has zero effect on the muscles. I've tried (absolute) 10, 100, 500, and 1000 and they all look the same. What's the best way to get the muscles to stiffen up and look less goopy?

What's the correct way to attach the muscle to bones? It seems I can use the MusclePaint> Muscle End Mask or I can use the Muscle to bone mask. Also, when you use a MusclePaint SOP does that override any distance threshold that is set in the MuscleConstraintPropertiesVellum SOP?

When I use the Muscle To Muscle constraints. The Muscle attachments cause spikes in the muscle geo like every other vertex is being pulled. I've found Muscle Glue Mask yields a cleaner result I'll attach some pics as well

Is there a way to sculpt a custom flexed shape for muscles? It looks like in the file Mio_muscle_setup from the Unreal demo the artist used an Edit and Femdeform SOP to achieve this on the bicep but it's not clear to me how it works or to set this up in my own file.

Any insight / help would be amazing!
Jeff

forgot to include the muscle and bone alembic cache Here they are

jmbrodsky
... What's the best way to get the muscles to stiffen up and look less goopy?

With the constraints setup as they are in the MuscleSolverVellum node, we can't get perfectly rigid muscles. A built-in ShapeMatch constraint would have been one way to do that, but in practicality it would serve more fringe use cases. Maybe something to include in the future?
Nevertheless, in your hip file, it would be advisable to include "some amount" of MuscleToBone constraint. This will help the constraint system hold muscles in place and not flop around.
The modified hipfile below manages to ungoop your muscles without the help of the muscletobone constraint, and with fairly low substeps. The main problem was the muscle Damping wasn't low enough to get a response from the shape stiffness. More substeps and constraint iterations could also help.
This, and other changes are commented in the attached modified hip file.

jmbrodsky
What's the correct way to attach the muscle to bones? It seems I can use the MusclePaint> Muscle End Mask or I can use the Muscle to bone mask. Also, when you use a MusclePaint SOP does that override any distance threshold that is set in the MuscleConstraintPropertiesVellum SOP?

Ideally the MusclePaint node should come after MuscleConstraintProperties. ie, use the parameters to get your constraint masks as far as you can, then use MusclePaint to refine.
In your specific case, the paint node was upstream, and muscletobonemask was being initialized to zero. The downstream MuscleConstraintProperties node was not overwriting this value because Mask Falloff wasn't toggled on. The zero value was just passing through.
MusclePaint does not affect the muscletobonedistance attribute.

jmbrodsky
When I use the Muscle To Muscle constraints. The Muscle attachments cause spikes in the muscle geo like every other vertex is being pulled. I've found Muscle Glue Mask yields a cleaner result I'll attach some pics as well

With weaker material properties and low substeps, MuscleToMuscle will potentially pull points into spikes. Internally, MuscleToMuscle uses Vellum Stitch, and MuscleGlue uses Vellum Glue. (The difference being one uses a point-to-prim attachment, and the latter uses a one point to multiple other points attachment -with no sliding).

jmbrodsky
Is there a way to sculpt a custom flexed shape for muscles? It looks like in the file Mio_muscle_setup from the Unreal demo the artist used an Edit and Femdeform SOP to achieve this on the bicep but it's not clear to me how it works or to set this up in my own file.

Yes. The workflow is described in this example available from the SideFX content library.
https://www.sidefx.com/contentlibrary/muscle-target-shape/ [www.sidefx.com]

@john this is really cool... thanks for taking the time! I really appreciate the notation in the file.