Chained Physics Constraints with Limited Linear Constraint Don't Work

When connecting physics constraints in sequence, and the top one has a Linear Limit Limit set the physics completely break. Increasing the number of substeps doesn’t fix this issue.

Repro Steps:

Create a blank project.

Add 4 cubes, 3 placed vertically offset from each other and the 4th one in line to collide with the bottom box (resize if desired, see picture for example). Set physics on all but the top box to simulate.


Vertical cubes are highlighted, the top two are resized to be smaller.

Add two physics constraints, one from the top box to the middle box, one from the middle box to the bottom box. Set a limit in the linear limit section of the first constraint (I set mine to 75).

Increase the mass of the 4th (offset) box.

Press play.

What happens:
The two bottom boxes start quickly vibrating, and shortly progress to rapidly teleporting around the local vicinity.

Note: Setting the limits to be soft displays the same behaviour.

What’s expected/desired?
The boxes are suspended at the defined height below the boxes their tethered to. Collisions with the bottom box will cause the bottom and middle boxes to bump around (settling eventually if the physics properties are set correctly). This should happen independently of the weight of the bottom boxes.

I need to use linear limit limits because I need the cable that I’m simulating to be able to go slack when the cube is within the limit (as a rope would work). I need the two cables chained together because I’m simulating two ropes connected via a hook.

[Example project][2]

Hello Griffork,

Thank you for reporting this issue and for providing the example project. I’ve entered a bug report for the issue. You can track the bug report here: UE-48369.

Have a nice day!