[huxiaoyi-ovo]

Summary

Fixes #730.

Copied URDF/ETS robots can retain references to links in the original robot, causing copy().rne() to fail. The same problem affects coriolis() because nofriction() replaces the copied robot's links with another set of disconnected copies.

This PR addresses both root causes:

• Rebuild parent/child relationships during BaseRobot.__deepcopy__() using the existing parent-name resolution mechanism.
• Modify friction parameters directly on the copied robot's links instead of replacing nf._links.
• Add a regression test with two joints separated by a static link.

The test verifies correct parent/child references, unchanged original topology, matching inverse dynamics results, and successful coriolis() calculations.

Validation

Validated commit fbc9474 in [fork CI PR #2](huxiaoyi-ovo#2).

• Python 3.10–3.14 on Ubuntu, Windows and macOS: all passed.
• Core tests and aggregate test gate: passed.
• Coverage and documentation builds: passed.
• 19 successful jobs, 1 conditional skip, 0 failures.

Only three files changed. No public API signatures or inverse dynamics equations were modified.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 0 complexity · -2 duplication

Metric	Results
Complexity	0
Duplication	-2

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (31d99a9) to head (b5fa99b).

Files with missing lines	Patch %	Lines
src/roboticstoolbox/robot/Link.py	0.00%	16 Missing ⚠️
src/roboticstoolbox/robot/BaseRobot.py	0.00%	8 Missing ⚠️
src/roboticstoolbox/robot/Dynamics.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #732   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        146     146           
  Lines      17295   17304    +9     
=====================================
- Misses     17295   17304    +9     

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[petercorke]

Thank you for this, and for the careful test. I reproduced the problem: on main, copy() leaves each link tied to the original robot's links, and fkine on a copy fails. Your change fixes that. Before I merge it I'd like the fix made at its root rather than patched from outside. Three requests:

• Make Link.__deepcopy__ respect its memo argument, the dictionary that copy.deepcopy passes along, which maps each original object to the copy already made. Use it for the references, for example deepcopy(self.parent, memo) instead of self.parent, and record the new link in memo before copying them, since parent and child refer to each other. BaseRobot.__deepcopy__ then copies all the links with one shared memo, and the changes to _children, _parent_name and _parent can go.
• In nofriction, use Link.nofriction rather than setting B and Tc again by hand.
• Copy the grippers too. At the moment the copy of a Panda has no gripper, so fkine ends at a different frame from the original. Gripper modeling is being reconsidered in Rethink how grippers are modeled, and pause gripper-related changes #884, so keep that part small.

A test that copy().fkine(q) equals fkine(q) for a robot with a gripper would catch this.

[huxiaoyi-ovo]

Hi @petercorke, thanks for the detailed review.

I've updated the branch to address all three points: shared deepcopy memo handling for link topology, reusing Link.nofriction() without replacing links, and preserving the gripper links, tool transform and joint state.

I also added regression tests for the parent graph, RNE/Coriolis and Panda gripper FK consistency.

The revised head is b5fa99b. The [fork CI run](huxiaoyi-ovo#2) has passed the core suite (2,310 passed), and the remaining platform checks are still running.

ChatGPT assisted with code review and test preparation.