Link 8 showing up on PyPlot

[Muhammadsgit]

Is it possible to not show the link from the base to the end-effector?

qt = rtb.jtraj(robot.qr, q_pickup,50)
robot.plot(qt.q, backend='pyplot', movie='panda3.gif')

ERobot: panda (by Franka Emika), 7 joints (RRRRRRR), 1 gripper, geometry, collision
┌─────┬──────────────┬───────┬─────────────┬────────────────────────────────────────────────┐
│link │ link │ joint │ parent │ ETS: parent to link │
├─────┼──────────────┼───────┼─────────────┼────────────────────────────────────────────────┤
│ 0 │ panda_link0 │ │ BASE │ SE3() │
│ 1 │ panda_link1 │ 0 │ panda_link0 │ SE3(0, 0, 0.333) ⊕ Rz(q0) │
│ 2 │ panda_link2 │ 1 │ panda_link1 │ SE3(-90°, -0°, 0°) ⊕ Rz(q1) │
│ 3 │ panda_link3 │ 2 │ panda_link2 │ SE3(0, -0.316, 0; 90°, -0°, 0°) ⊕ Rz(q2) │
│ 4 │ panda_link4 │ 3 │ panda_link3 │ SE3(0.0825, 0, 0; 90°, -0°, 0°) ⊕ Rz(q3) │
│ 5 │ panda_link5 │ 4 │ panda_link4 │ SE3(-0.0825, 0.384, 0; -90°, -0°, 0°) ⊕ Rz(q4) │
│ 6 │ panda_link6 │ 5 │ panda_link5 │ SE3(90°, -0°, 0°) ⊕ Rz(q5) │
│ 7 │ panda_link7 │ 6 │ panda_link6 │ SE3(0.088, 0, 0; 90°, -0°, 0°) ⊕ Rz(q6) │
│ 8 │ @panda_link8 │ │ panda_link7 │ SE3(0, 0, 0.107) │
└─────┴──────────────┴───────┴─────────────┴────────────────────────────────────────────────┘

┌─────┬─────┬────────┬─────┬───────┬─────┬───────┬──────┐
│name │ q0 │ q1 │ q2 │ q3 │ q4 │ q5 │ q6 │
├─────┼─────┼────────┼─────┼───────┼─────┼───────┼──────┤
│ qr │ 0° │ -17.2° │ 0° │ -126° │ 0° │ 115° │ 45° │
│ qz │ 0° │ 0° │ 0° │ 0° │ 0° │ 0° │ 0° │
└─────┴─────┴────────┴─────┴───────┴─────┴───────┴──────┘

[PAdDyBook]

I have the same issue. also ik are different. did you solve the problem?

[Muhammadsgit]

Not yet and my ik matrix (sol) is different too than the one in the tutorial.

[petercorke]

Hi @Muhammadsgit and @PAdDyBook, thank you for your interest in RTB, and apologies for the very long delay in replying. Various life events got in the way, and since May this year I've been doing a lot of work across RTB, Swift and SpatialGeometry.

The extra line in the plot. This was a bug, now fixed. fkine_all() stopped computing link poses at the nominal end-effector link (panda_link8 for the Panda), so the gripper links (panda_hand and the fingers) were left at the world origin and drawn there, which gave the spurious line from the base to the end-effector. The fix is #643, in RTB 1.4.2 and later (see also #467 and #427). Please upgrade with pip install -U roboticstoolbox-python.

The IK solution. It is expected that your sol differs from the tutorial's. A 7-joint arm has many joint vectors that reach the same pose, and which one the solver returns depends on the starting point q0 and on random restarts. For example, I called ikine_LM three times with random q0 and got three quite different joint vectors, all reaching the target to within 1e-4 m. So compare solutions by checking robot.fkine(sol.q) against your target Tep and sol.success, not the joint values. For a repeatable result, pass your own q0.

If you still have a problem after upgrading, please post an Issue rather than a discussion thread, with a minimal example. Thanks for the questions.