Request for help with Joint Control for Unitree Go2 in Genesis

[Total-Bots-Lab]

Hello ,
I’m currently working with the Genesis simulator to control the Unitree Go2 robot using joint-level commands, following the official documentation here:
https://genesis-world.readthedocs.io/en/latest/user_guide/getting_started/control_your_robot.html#joint-control
Here’s the code I’m using (full code available at the end):

import genesis as gs
gs.init(backend=gs.cpu)
scene = gs.Scene(show_viewer=True)
plane = scene.add_entity(gs.morphs.Plane())
robot = gs.morphs.MJCF(file="xml/Unitree_Go2/go2.xml")
Go2 = scene.add_entity(robot)
scene.build()
jnt_names = [
    'FL_hip_joint', 'FL_thigh_joint', 'FL_calf_joint',
    'FR_hip_joint', 'FR_thigh_joint', 'FR_calf_joint',
    'RL_hip_joint', 'RL_thigh_joint', 'RL_calf_joint',
    'RR_hip_joint', 'RR_thigh_joint', 'RR_calf_joint',
]
dofs_idx = [Go2.get_joint(name).dof_idx_local for name in jnt_names]
print(dofs_idx)

The output is:

[[0, 1, 2, 3, 4, 5], 10, 14, 7, 11, 15, 8, 12, 16, 9, 13, 17]

Then I try to set joint positions like this:

import numpy as np
for i in range(150):
    Go2.set_dofs_position(np.array([0, 10, 14, 7, 11, 15, 8, 12, 16, 9, 13, 17]), dofs_idx)
    scene.step()

But I keep getting this error:

TypeError: can only concatenate list (not "int") to list

I’ve tried many variations, but nothing works.
Can anyone help me figure out how to correctly apply joint positions to the Go2?
✅ Full code is available here:
📂 total_robotics/genesis_AI_sims/Unitree_Go2/understanding_action_space
📎 https://github.com/Total-Bots-Lab/total_robotics.git

I will be grateful if you kindly help me.

Thanks in advance
Ritwik

Here I am giving the detailed output of the code:

Cell 2: Getting the joint dof info

# Getting the joint Info Go2
jnt_names = [
    'FL_hip_joint',
    'FL_thigh_joint',
    'FL_calf_joint',
    'FR_hip_joint',
    'FR_thigh_joint',
    'FR_calf_joint',
    'RL_hip_joint',
    'RL_thigh_joint',
    'RL_calf_joint',
    'RR_hip_joint',
    'RR_thigh_joint',
    'RR_calf_joint', 
]
dofs_idx = [Go2.get_joint(name).dof_idx_local for name in jnt_names]
print(dofs_idx)

Output:

[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[Genesis] [10:18:29] [WARNING] This property is deprecated and will be removed in future release. Please use 'dof_idx_local' instead.
[[0, 1, 2, 3, 4, 5], 10, 14, 7, 11, 15, 8, 12, 16, 9, 13, 17]

Cell 3: Try 1 to apply action

# Hard reset
import numpy as np
for i in range(150):
    if i < 50:
        Go2.set_dofs_position(np.array([[0, 0, 0, 0, 0, 0], 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
    elif i < 100:
        Go2.set_dofs_position(np.array([[1, 1, 1, 1, 1, 1], 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)
    else:
        Go2.set_dofs_position(np.array([[2, 2, 2, 2, 2, 2], 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]), dofs_idx)

    scene.step()

Output:

---

ValueError Traceback (most recent call last)
Cell In[3], line 5
3 for i in range(150):
4 if i < 50:
----> 5 Go2.set_dofs_position(np.array([[0, 0, 0, 0, 0, 0], 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
6 elif i < 100:
7 Go2.set_dofs_position(np.array([[1, 1, 1, 1, 1, 1], 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)

ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 1 dimensions. The detected shape was (12,) + inhomogeneous part.

Cell 3: I tried to change the input by making it flattened (one dimension)

# Hard reset
import numpy as np
for i in range(150):
    if i < 50:
        Go2.set_dofs_position(np.array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
    elif i < 100:
        Go2.set_dofs_position(np.array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)
    else:
        Go2.set_dofs_position(np.array([2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]), dofs_idx)

    scene.step()

Output:

TypeError                                 Traceback (most recent call last)
Cell In[4], line 5
      3 for i in range(150):
      4     if i < 50:
----> 5         Go2.set_dofs_position(np.array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
      6     elif i < 100:
      7         Go2.set_dofs_position(np.array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)

File ~\Genesis\genesis\utils\misc.py:72, in assert_built.<locals>.wrapper(self, *args, **kwargs)
     70 if not self.is_built:
     71     gs.raise_exception("Scene is not built yet.")
---> 72 return method(self, *args, **kwargs)

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:2144, in RigidEntity.set_dofs_position(self, position, dofs_idx_local, envs_idx, zero_velocity, unsafe)
   2128 @gs.assert_built
   2129 def set_dofs_position(self, position, dofs_idx_local=None, envs_idx=None, *, zero_velocity=True, unsafe=False):
   2130     """
   2131     Set the entity's dofs' position.
   2132 
   (...)
   2142         Whether to zero the velocity of all the entity's dofs. Defaults to True. This is a safety measure after a sudden change in entity pose.
   2143     """
-> 2144     dofs_idx = self._get_idx(dofs_idx_local, self.n_dofs, self._dof_start, unsafe=True)
   2145     self._solver.set_dofs_position(position, dofs_idx, envs_idx, unsafe=unsafe, skip_forward=zero_velocity)
   2146     if zero_velocity:

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:1992, in RigidEntity._get_idx(self, idx_local, idx_local_max, idx_global_start, unsafe)
   1990     idx_global = idx_local + idx_global_start
   1991 elif isinstance(idx_local, (list, tuple)):
-> 1992     idx_global = [i + idx_global_start for i in idx_local]
   1993 else:
   1994     # Increment may be slow when dealing with heterogenuous data, so it must be avoided if possible
   1995     if idx_global_start > 0:

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:1992, in <listcomp>(.0)
   1990     idx_global = idx_local + idx_global_start
   1991 elif isinstance(idx_local, (list, tuple)):
-> 1992     idx_global = [i + idx_global_start for i in idx_local]
   1993 else:
   1994     # Increment may be slow when dealing with heterogenuous data, so it must be avoided if possible
   1995     if idx_global_start > 0:

TypeError: can only concatenate list (not "int") to list

Cell 3: Another try with 12 element array

# Hard reset
import numpy as np
for i in range(150):
    if i < 50:
        Go2.set_dofs_position(np.array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
    elif i < 100:
        Go2.set_dofs_position(np.array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)
    else:
        Go2.set_dofs_position(np.array([2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]), dofs_idx)

    scene.step()

Output:

TypeError                                 Traceback (most recent call last)
Cell In[5], line 5
      3 for i in range(150):
      4     if i < 50:
----> 5         Go2.set_dofs_position(np.array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dofs_idx)
      6     elif i < 100:
      7         Go2.set_dofs_position(np.array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]), dofs_idx)

File ~\Genesis\genesis\utils\misc.py:72, in assert_built.<locals>.wrapper(self, *args, **kwargs)
     70 if not self.is_built:
     71     gs.raise_exception("Scene is not built yet.")
---> 72 return method(self, *args, **kwargs)

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:2144, in RigidEntity.set_dofs_position(self, position, dofs_idx_local, envs_idx, zero_velocity, unsafe)
   2128 @gs.assert_built
   2129 def set_dofs_position(self, position, dofs_idx_local=None, envs_idx=None, *, zero_velocity=True, unsafe=False):
   2130     """
   2131     Set the entity's dofs' position.
   2132 
   (...)
   2142         Whether to zero the velocity of all the entity's dofs. Defaults to True. This is a safety measure after a sudden change in entity pose.
   2143     """
-> 2144     dofs_idx = self._get_idx(dofs_idx_local, self.n_dofs, self._dof_start, unsafe=True)
   2145     self._solver.set_dofs_position(position, dofs_idx, envs_idx, unsafe=unsafe, skip_forward=zero_velocity)
   2146     if zero_velocity:

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:1992, in RigidEntity._get_idx(self, idx_local, idx_local_max, idx_global_start, unsafe)
   1990     idx_global = idx_local + idx_global_start
   1991 elif isinstance(idx_local, (list, tuple)):
-> 1992     idx_global = [i + idx_global_start for i in idx_local]
   1993 else:
   1994     # Increment may be slow when dealing with heterogenuous data, so it must be avoided if possible
   1995     if idx_global_start > 0:

File ~\Genesis\genesis\engine\entities\rigid_entity\rigid_entity.py:1992, in <listcomp>(.0)
   1990     idx_global = idx_local + idx_global_start
   1991 elif isinstance(idx_local, (list, tuple)):
-> 1992     idx_global = [i + idx_global_start for i in idx_local]
   1993 else:
   1994     # Increment may be slow when dealing with heterogenuous data, so it must be avoided if possible
   1995     if idx_global_start > 0:

TypeError: can only concatenate list (not "int") to list

[duburcqa]

Can you provide the complete traceback of the error?

[Total-Bots-Lab]

Hello,
Thanks for your reply. I have edited my description and have given the outputs.

[duburcqa]

The issue is that dofs_idx must be a flat list of integers, not a nested list. Here is how to properly complete dofs_idx:

motor_dofs = [i for name in joint_names for i in robot.get_joint(name).dofs_idx_local]

The same goes for the setters. The values must be flattened.

[Total-Bots-Lab]

Thanks a lot for your response. The code is working in terms of accepting action. However, there still exists some confusion.

The output is get for the following code is as presented.

Code

# Getting the joint Info Go2
joint_names = [
    'FL_hip_joint',
    'FL_thigh_joint',
    'FL_calf_joint',
    'FR_hip_joint',
    'FR_thigh_joint',
    'FR_calf_joint',
    'RL_hip_joint',
    'RL_thigh_joint',
    'RL_calf_joint',
    'RR_hip_joint',
    'RR_thigh_joint',
    'RR_calf_joint', 
]
motor_dofs = [i for name in joint_names for i in Go2.get_joint(name).dofs_idx_local]
motor_dofs

Output

[0, 1, 2, 3, 4, 5, 10, 14, 7, 11, 15, 8, 12, 16, 9, 13, 17]

Now, the question is

1. Why are the numbers not in sequence
2. Why is number 6 missing
3. How do I interface and interpret 17 inputs for 12 joints? How I map it.

Can you kindly refer any documents for the same or help me to understand better ?

P.S. I am getting output also when I apply the code

Go2.set_dofs_position(motor_dofs,motor_dofs)

But I can't interpret the code with the output.

[duburcqa]

I’m sorry but these are generic robotics and software engineering question not specific to Genesis. I cannot spend time answering to this kind of questions for everybody. I guess asking ChatGPT, it should do a great job.

[Total-Bots-Lab]

Can you kindly not close the discussion? So that someone else from the community can help me? I am still struggling with the issue, and ChatGPT can't solve it. I am requesting that you mark the discussion as solved.

[duburcqa]

1. Why are the numbers not in sequence 2. Why is number 6 missing

First, you are specifically requesting to extract the degrees of freedom corresponding to

joint_names = [
    'FL_hip_joint',
    'FL_thigh_joint',
    'FL_calf_joint',
    'FR_hip_joint',
    'FR_thigh_joint',
    'FR_calf_joint',
    'RL_hip_joint',
    'RL_thigh_joint',
    'RL_calf_joint',
    'RR_hip_joint',
    'RR_thigh_joint',
    'RR_calf_joint', 
]

so it has absolutely zero guarantee to be in sequence, nor to contain all integers without missing values.

If you want to process the joint in order, to can get their names:

for joint in Go2.joints:
    print(joint.name)

but then it becomes completely irrelevant to specify dofs_local using a mask since it is used for re-ordering or filtering.

3. How do I interface and interpret 17 inputs for 12 joints? How I map it.

You may have several degrees of freedom per joint. This is typically the case for the floating base (root joint) that has 6 DoFs (3 translations, 3 rotations, in this exact order). The 3 rotations are Euler angles typically returned by gs.utils.geom.quat_to_xyz.

[Total-Bots-Lab]

Thanks a lot for your reply. I am working on it.