error when plotting Planar_Y robot

[durka]

Describe the bug
When attempting to make a noodle plot of the ETS.Planar_Y model, it partially plots, but encounters an error and does not show the whole thing (only one link I believe).

Version information

• roboticstoolbox 0.11.0 installed from PyPI
• spatialmath 0.11 installed from PyPI

To Reproduce
Steps to reproduce the behavior:

1. The shortest, complete, Python script that exhibits the bug.

import roboticstoolbox as rtb
r = rtb.models.ETS.Planar_Y()
r.plot(r.qz)

2. The script output, including error messages.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/roboticstoolbox/robot/Robot.py", line 1442, in plot
    env.step(dt)
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/roboticstoolbox/backends/PyPlot/PyPlot.py", line 203, in step
    robot.draw()
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/roboticstoolbox/backends/PyPlot/RobotPlot.py", line 106, in draw
    self.links[0].set_3d_properties(points[:, 2])
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/mpl_toolkits/mplot3d/art3d.py", line 175, in set_3d_properties
    zs = np.broadcast_to(zs, len(xs))
  File "<__array_function__ internals>", line 5, in broadcast_to
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/numpy/lib/stride_tricks.py", line 411, in broadcast_to
    return _broadcast_to(array, shape, subok=subok, readonly=True)
  File "/home/alex/.cache/pypoetry/virtualenvs/sim-bd0j9NSV-py3.9/lib/python3.9/site-packages/numpy/lib/stride_tricks.py", line 348, in _broadcast_to
    it = np.nditer(
ValueError: operands could not be broadcast together with remapped shapes [original->remapped]: (4,)  and requested shape (3,)

Expected behavior
I was really hoping this would be a simple way to make noodle plots for branched kinematic trees (without having to write a giant URDF nightmare with 3D meshes etc), so I'll be disappointed if the root cause of this is that it simply isn't really supported.

Environment (please complete the following information):

• Ubuntu 20.04
• Python 3.9

[petercorke]

Hopefully something simple, it worked a couple of months back, will check it out in the next day or so.

[jhavl]

This has been fixed on the future branch, will be incorporated into the next release