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Added property to Symbolics that returns the ground reaction force vector expressions. #35

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Merged
moorepants merged 1 commit into from
May 21, 2026
Merged

Added property to Symbolics that returns the ground reaction force vector expressions. #35

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18 changes: 17 additions & 1 deletion pygait2d/derive.py
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,8 @@ class Symbolics():
speeds : list of Function(t)
The generalized speeds of the system.
states : list of Function(t)
ground_reaction_forces : dictionary
Force vectors acting on the right and left foot toe and heel points.

"""
# TODO : Add these as properties.
Expand Down Expand Up @@ -164,6 +166,20 @@ def joint_torques(self):
elif len(self.specifieds) == 10:
return self.specifieds[3:-1]

@property
def ground_reaction_forces(self):
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"""Returns a dictionary the ground reaction force vectors expressed in
the inertial reference frame acting on the heel and toe of each foot.
Keys are ``'Right Foot heel', 'Right Foot toe', 'Left Foot heel',
'Left Foot toe'``."""
grfs = {}
for load in self.kanes_method.loads:
point_name = load[0].name
if point_name in ['Right Foot heel', 'Right Foot toe',
'Left Foot heel', 'Left Foot toe']:
grfs[point_name] = load[1]
return grfs


def generate_gait_cycle_torque_controller(coordinates, speeds, specified):
# joint_torques(phase) = mean_joint_torque + K*(joint_state_desired -
Expand Down Expand Up @@ -424,7 +440,7 @@ def derive_equations_of_motion(

segment_class, desc, joint_desc = segment_descriptions[label]
passive_torque = passive_torques # true or false for this particular segment

if label == 'A': # trunk
parent_reference_frame = ground
origin_joint = origin
Expand Down
17 changes: 9 additions & 8 deletions pygait2d/utils.py
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Expand Up @@ -307,14 +307,15 @@ def plot(sym, times, x, r, p, follow=None):

# show ground reaction force vectors at the heels and toes, scaled to
# visually reasonable length
#scene.add_vector(contact_force(rfoot.toe, ground, origin, v)/600.0,
#rfoot.toe, color="tab:blue")
#scene.add_vector(contact_force(rfoot.heel, ground, origin, v)/600.0,
#rfoot.heel, color="tab:blue")
#scene.add_vector(contact_force(lfoot.toe, ground, origin, v)/600.0,
#lfoot.toe, color="tab:blue")
#scene.add_vector(contact_force(lfoot.heel, ground, origin, v)/600.0,
#lfoot.heel, color="tab:blue")
grf = sym.ground_reaction_forces
scene.add_vector(grf['Right Foot toe']/600.0, rfoot.toe,
color="tab:blue")
scene.add_vector(grf['Right Foot heel']/600.0, rfoot.heel,
color="tab:blue")
scene.add_vector(grf['Left Foot toe']/600.0, lfoot.toe,
color="tab:blue")
scene.add_vector(grf['Left Foot heel']/600.0, lfoot.heel,
color="tab:blue")

scene.lambdify_system(sym.states + sym.specifieds + sym.constants)
scene.evaluate_system(*np.hstack((x, r, p)))
Expand Down
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