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fix: honour flip in DHLink.A() when the joint ET is not last (#563) #619

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fix: honour flip in DHLink.A() when the joint ET is not last (#563) #619

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2 changes: 1 addition & 1 deletion src/roboticstoolbox/robot/DHLink.py
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Original file line number Diff line number Diff line change
Expand Up @@ -616,7 +616,7 @@ def A(self, q: float) -> SE3:
sa = _sin(self.alpha)
ca = _cos(self.alpha)

if self.ets[-1].isflip:
if self.isflip:
q = -q + self.offset
else:
q = q + self.offset
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11 changes: 11 additions & 0 deletions tests/test_DHRobot.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1564,6 +1564,17 @@ def test_alpha(self):

nt.assert_array_almost_equal(r0.alpha, np.r_[1, 0, -1, 1, -1, 0] * math.pi / 2)

def test_flip_with_nonzero_a(self):
# Issue #563: DHLink.A() honoured flip only when the joint ET happened
# to be the last ET. For a link with a nonzero a/d/alpha the joint ET is
# not last, so flip=True was silently ignored and q was not negated.
q = 0.5
L = rp.RevoluteDH(a=1.0, flip=True)
# A(q) must agree with the link's own ETS evaluation, which honours flip.
nt.assert_array_almost_equal(L.A(q).A, L.ets.eval([q]))
# The rotation uses the negated angle, so the [1, 0] entry is sin(-q).
nt.assert_almost_equal(L.A(q).A[1, 0], math.sin(-q))

def test_ets(self):
panda = rp.models.DH.Panda()
panda.ets()
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