 Here is a simplified version of the Python code using the `pytransform3d` library and `urdf` for loading the robot model. Note that this code assumes you have a URDF file named `robot.urdf` in the same directory.

```python
import pytransform3d as p3d
import urdf
import numpy as np
from matplotlib import pyplot as plt

# Load the robot model from URDF
robot = urdf.load_urdf_file('robot.urdf')

# Define the spherical mass properties
mass = 1.0  # mass of the spherical mass
radius = 0.1  # radius of the spherical mass

# Define the force/torque sensor at the tool center point (TCP)
force = np.array([1.0, 0.0, 0.0])  # force component in N
torque = np.array([0.0, 0.5, 0.0])  # torque component in Nm

# Define the screw axis and parameters for the wrench
axis = p3d.Vector3d(0, 0, 1)
params = p3d.ScrewParameters(force, torque, axis)

# Define the transformation from the TCP to the base frame
base_to_tcp = p3d.Transform3d.from_matrix(np.eye(4))  # identity transformation for now

# Function to plot the transformation about and along a screw axis
def plot_screw(screw, color='r', label=None):
    axis, params = screw
    direction = axis.normalized()
    point = direction * params.w
    ellipsoid = p3d.to_ellipsoid(params.v, params.w)
    artists = p3d._objects_to_artists([ellipsoid, p3d.vector_to_point(point, color=color), p3d.vector_to_direction(direction, color=color)])
    if label:
        artists[-1].set_label(label)
    return artists

# Transform the wrench from the TCP to the base frame using the adjoint representation of the transformation
adjoint = base_to_tcp.adjoint()
transformed_params = p3d.Transform3d.from_matrix(adjoint).apply_screw(params)

# Plot the wrench in the TCP frame
plot_screw((axis, params), label='Wrench (TCP)')

# Set joint angles
q = np.array([0.1, 0.2, 0.3, 0.4, 0.5, 0.6])

# Plot the robot model and the transformed wrench in the base frame
fig, ax = plt.subplots()
robot_artists = p3d._objects_to_artists([robot])
for artist in robot_artists:
    artist.set_zorder(1)

# Add the spherical mass
mass_point = p3d.vector_to_point(p3d.Vector3d(0, 0, radius), color='b')
ax.add_artist(mass_point)

# Add the transformed wrench in the base frame
plot_screw((axis, transformed_params), label='Wrench (Base)')

# Plot the TCP
tcp_point = p3d.vector_to_point(base_to_tcp.translation, color='g')
ax.add_artist(tcp_point)

# Set the plot limits
ax.set_xlim(-1, 1)
ax.set_ylim(-1, 1)
ax.set_zlim(-1, 1)

# Show the plot and save as an image
plt.show()
plt.savefig('robot_arm_wrench.png')
```

This code will load a robot model from a URDF file, set joint angles, and visualize the robot arm, the tool center point (TCP), the spherical mass, and the wrench in both the TCP frame and the base frame. The wrench is transformed from the TCP to the robot's base frame using the adjoint representation of the transformation. The visualization is saved as an image named `robot_arm_wrench.png`.