Left HindLeg breaks when creating Modular Control Rig in Unreal Engine 5.8

Hi everyone,

I am working on a Modular Control Rig for a hybrid/creature character in Unreal Engine 5.8, and I am facing an issue with the Left HindLeg module.

The character has an animal-style leg hierarchy, so I am using the HindLeg module instead of the normal Leg module. My leg bone chain is similar to this:


FemNis-L-Thigh
 └── FemNis-L-Calf
      └── FemNis-L-HorseLink
           └── FemNis-L-Foot

For the left HindLeg module, I connected it like this:


HindLeg Primary    → thigh_l_socket
Thigh              → FemNis-L-Thigh
Upper Knee         → FemNis-L-Calf
Lower Knee         → FemNis-L-HorseLink
Foot Bone          → FemNis-L-Foot
Pole Vector Parent → root_ctrl
Settings Control   → global_ctrl
Parent Control     → root_ctrl

The socket thigh_l_socket is created under the FemNis-L-Thigh bone in the Skeleton asset.

The problem is that when I compile the Modular Rig or try to move/test the leg control, the left hind leg breaks/deforms incorrectly. The control appears, but the leg does not behave properly. It looks like the IK chain or knee/hock direction is solving incorrectly.

The right side is either working better or is easier to configure, but the left HindLeg specifically breaks.

Things I have already checked:


- The socket is placed under the correct thigh bone
- Parent Control and Pole Vector Parent are set to root_ctrl
- Settings Control is set to global_ctrl
- I am using HindLeg because the skeleton has a HorseLink/hock-style joint
- I compiled and saved after setting the module

My questions:

  1. For a HindLeg chain like Thigh → Calf → HorseLink → Foot, should Upper Knee be the calf and Lower Knee be the HorseLink?
  2. Is there a specific axis setting I need to adjust for the HindLeg module?
  3. Could this be related to the character’s bone orientation or mirrored left-side axis?
  4. Is there a recommended setup for creature/hybrid legs using the Modular Control Rig HindLeg module in UE 5.8?

Any guidance would be really appreciated. I can share screenshots of the bone hierarchy and module settings if needed.

Thanks.