The error you are encountering seems to originate from therne function within theroboticstoolbox library. Specifically, the issue arises due to an invalid index when accessing thev[jp] variable, wherejp isNone. This means that the parent link for the current joint is not being set correctly, leading to the TypeError when indexing.

In the Panda robot model, each joint should have a valid parent link. Ifjp isNone, it implies that the model isn't correctly assigning parent-child relationships between joints. Here's how you can troubleshoot:

1. Check for Compatibility: Ensure that theroboticstoolbox version you're using is compatible with your robot model. The Panda robot model has 7 degrees of freedom, and the dynamic functions (likefdyn) depend on the robot's structure being correctly initialized. Updating theroboticstoolbox library might resolve any internal issues with how the model is loaded.

2. Controller Function Signature: Make sure thedumbcontroller function is correct in terms of its arguments and return type. It's expected to return a valid control input (tau), but currently, it returns all zeros, which might cause issues if the robot expects certain torques or forces to be applied. You could try returning small values or testing with different control signals.

   defdumbcontroller(robot,t,q,qd):# Apply small control values to avoid issues with zero torquesreturnnumpy.array([0.01,0.01,0.01,0.01,0.01,0.01,0.01])

3. Inspect Robot Model: Check if the Panda robot model is correctly loaded. You could inspect the robot’s joints and links to ensure there are no issues with the parent-child hierarchy:

   print(robot)

This error reminds me of how small setup details in complex projects, like yours with university enrollment analysis, can have cascading effects. Just like correctly normalizing enrollment data over the years helps avoid inconsistencies in trends, setting up the robot's structure correctly is crucial to smooth dynamics simulation.

If you're still stuck after trying the above, you could explore using a different robot model temporarily to see if the issue persists across models. Let me know how it goes!

Thanks for the response. The problem turned out to be that the Panda model doesn't have dynamics parameters (mainly inertias, I think). It was a kinematics only model. The other robot arms I tried were also kinematics-only, so they all threw the same error. Temporarily switching to the Puma model, which does have dynamics parameters, fixed the problem.