Constraint Network Anchor centered between two other anchors

[bonjarry]

I have two packed rbds connected by a constraint network.

At the center of the constraint (halfway between the two objects), I have a third anchor point.

I would like this point to stay at the center even if the distance between them changes (spring constraint).

From the docs (http://www.sidefx.com/docs/houdini15.5/nodes/dop/constraintnetwork), I have set the anchor_id=-1 to keep it relative to one of the objects, but this isn't exactly what I'm trying to do.

I also tried using a sop solver in dops to reset the position of the "centroid" anchor each timestep, but this seemed to make the simulation unstable.
The anchor was positioned correctly, but the constraints themselves were behaving odd.  I'm wondering if manually setting the position of an anchor messes up the forces/attributes associated with that constraint?

(This is a simplified case of a larger setup, I can try to put together an example hipfile if that will make more sense)

[BRZ32]

Hey J,

I was playing with something similar earlier, constraints are tough. >.< So far i've not had much luck trying to manually set a constraints location in a sopsolver either, they tend to float away and the centroid of the constraint gets messed up . I'm still trying to figure these out but sometimes a wall to bounce things off of helps.

This center anchor, I'm imagining you're making something similar to those clacker-ball toys? So you're hard constraining the mid point to something else, like a character and you have two springs holding the packed objects to that pin? Or... is it more you've got a mid anchor that needs to dynamically find the center of those two constraints as they move about like a weighted ball in the middle of a string that a character is holding each end in one hand?

To illustrate like O----------------O----------------O

is the character holding the pin^ here and swinging it about

To illustrate like O----------------O----------------O
or is it holding   ^ this end and the other one^ here and the object in the middle needs to find its position dynamically?

[bonjarry]

It's similar to the second illustration, where the two ends are being moved, so i need to reset the center dynamically.

[BRZ32]

Have you tried using spring constraints with a rest length? Given the right strength values, the two springs should kind of fight one another and continually pull the ball to the center.