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Fix Previous-Pose Updates for Kinematic Rigid Bodies (VBD)#1447

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eric-heiden merged 3 commits into
newton-physics:mainfrom
jumyungc:rigid-vbd-kinematic-friction
Jan 23, 2026
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Fix Previous-Pose Updates for Kinematic Rigid Bodies (VBD)#1447
eric-heiden merged 3 commits into
newton-physics:mainfrom
jumyungc:rigid-vbd-kinematic-friction

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@jumyungc jumyungc commented Jan 23, 2026 •
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Description

The previous pose was being updated incorrectly for kinematic rigid bodies; it’s now fixed with just a few lines of change.

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Please ensure the migration guide for warp.sim users is up-to-date with the changes made in this PR.

  • The migration guide in docs/migration.rst is up-to date

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  • Necessary tests have been added and new examples are tested (see newton/tests/test_examples.py)
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Summary by CodeRabbit

  • Refactor

    • Optimized rigid body state tracking and internal velocity calculation timing for improved physics simulation consistency.
    • Improved joint state propagation handling during solver finalization.

  • Tests

    • Added new test coverage for cable gripper interactions with dynamic objects.

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@jumyungc
Proper prev pose update for kinematic rigid bodies.
5037eb8 
Signed-off-by: JC <jumyungc@nvidia.com>
@jumyungc
Better initialization of the prev body pose.
10fcbee 
Signed-off-by: JC <jumyungc@nvidia.com>
@jumyungc jumyungc added this to the 1.0 Release milestone Jan 23, 2026
@jumyungc jumyungc self-assigned this Jan 23, 2026
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📝 Walkthrough

Walkthrough

The PR modifies the timing of when the previous rigid body pose (body_q_prev) is captured during forward integration. Instead of capturing at the start of the forward step, the code now refreshes it at the end of the velocity update step. Parameter ordering in update_body_velocity is reordered, initial history initialization is adjusted, and a new kinematic gripper test is added.

Changes

Cohort / File(s) Summary
Rigid body solver kernels
newton/_src/solvers/vbd/rigid_vbd_kernels.py		 Removed body_q_prev write-back from forward step start; reordered update_body_velocity parameters to move body_q_prev after body_com; updated docstrings to document that previous pose is refreshed at kernel end.
Solver finalization and initialization
newton/_src/solvers/vbd/solver_vbd.py		 Changed body_q_prev initialization from zeros to clone of current model.body_q; updated update_body_velocity kernel call signature to match new parameter order; removed outputs from Dahl state arrays (joint_sigma_prev, joint_kappa_prev, joint_dkappa_prev) in joint kernel invocation.
Cable/gripper test
newton/tests/test_cable.py		 Added _drive_gripper_boxes_kernel to animate kinematic gripper trajectories; added _cable_kinematic_gripper_picks_capsule_impl test validating gripper-capsule interaction and lift dynamics; registered test via add_function_test.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related issues

Suggested labels

bug

Suggested reviewers

  • AnkaChan
  • eric-heiden
🚥 Pre-merge checks | ✅ 3
✅ Passed checks (3 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly and concisely summarizes the main change: fixing previous-pose updates specifically for kinematic rigid bodies in the VBD solver, which aligns with the key modifications across the three files (kernel signature reordering, initialization changes, and test additions).
Docstring Coverage ✅ Passed Docstring coverage is 88.89% which is sufficient. The required threshold is 80.00%.

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✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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@eric-heiden eric-heiden requested a review from Copilot January 23, 2026 19:43
Copilot AI reviewed Jan 23, 2026
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Pull request overview

This PR fixes a bug where the previous pose (body_q_prev) was not being updated correctly for kinematic rigid bodies in the VBD solver, leading to incorrect finite-difference velocity calculations and spurious friction forces.

Changes:

  • Moved the body_q_prev update from forward_step_rigid_bodies (which kinematic bodies exit early from) to update_body_velocity (which runs for all bodies)
  • Initialize body_q_prev by cloning the model's initial poses instead of using zeros to avoid spurious velocities on the first timestep
  • Added comprehensive test validating that kinematic bodies can transfer motion to dynamic bodies via friction

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File Description
newton/_src/solvers/vbd/rigid_vbd_kernels.py Removed premature body_q_prev update in forward_step_rigid_bodies; added pose refresh at end of update_body_velocity to capture both dynamic and kinematic body poses
newton/_src/solvers/vbd/solver_vbd.py Changed body_q_prev initialization to clone model poses instead of zeros; updated kernel launch parameters for consistency
newton/tests/test_cable.py Added test kernel and regression test validating kinematic friction transfer (gripper picking up capsule)

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@eric-heiden eric-heiden added this pull request to the merge queue Jan 23, 2026
Merged via the queue into newton-physics:main with commit 4f11e49 Jan 23, 2026
28 checks passed
@jumyungc jumyungc deleted the rigid-vbd-kinematic-friction branch January 24, 2026 00:39
eric-heiden pushed a commit to eric-heiden/newton that referenced this pull request Jan 28, 2026
@jumyungc
Fix Previous-Pose Updates for Kinematic Rigid Bodies (VBD) (newton-ph…
7c32a98 
…ysics#1447)

Signed-off-by: JC <jumyungc@nvidia.com>
@coderabbitai coderabbitai Bot mentioned this pull request Feb 11, 2026
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@coderabbitai coderabbitai Bot mentioned this pull request Feb 24, 2026
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@coderabbitai coderabbitai Bot mentioned this pull request Mar 9, 2026
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mmacklin pushed a commit to mmacklin/newton that referenced this pull request Apr 7, 2026
@jumyungc
Fix Previous-Pose Updates for Kinematic Rigid Bodies (VBD) (newton-ph…
0e96999 
…ysics#1447)

Signed-off-by: JC <jumyungc@nvidia.com>
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