= Roboticist
A <roboticist> develops or studies <robots> by combining their mechanical design, sensing, computation and control. The work connects a desired physical task to a machine that can actually perform it. <Kinematics> describes permitted motion; <robot motion planning> selects motions subject to constraints; <feedback control> uses measurements to correct execution. An algorithm and the apparatus it controls must therefore be evaluated together.
For an original planar <robot arm> example, let two links have lengths $l_1,l_2$ and relative joint angles $\theta_1,\theta_2$. Its <end effector> position is
$$
x=l_1\cos\theta_1+l_2\cos(\theta_1+\theta_2),\qquad
y=l_1\sin\theta_1+l_2\sin(\theta_1+\theta_2).
$$
With both lengths $0.5\,\mathrm m$ and angles $(0,\pi/2)$, the endpoint is $(0.5,0.5)\,\mathrm m$. A small first-joint offset $\delta\theta_1=0.01$ radians changes the position to first order by $(-y,x)\delta\theta_1=(-0.005,0.005)\,\mathrm m$, an error magnitude about $7.07\,\mathrm{mm}$. Accurate commanded numbers do not imply equally accurate physical geometry.
A proposed investigation compares measured endpoint positions with the <kinematics> model over several configurations, then checks whether the discrepancies follow a joint offset, a link-length error or changing mechanical deflection. Those alternatives suggest different corrections. It also tests execution on the real <robot>, rather than treating successful numerical planning as sufficient evidence of task completion.
<Kris Hauser>'s author-hosted <Robotic Systems by Kris Hauser> connects geometric configurations, <inverse kinematics>, motion selection and contact constraints in one technical account.<Robotic Systems by Kris Hauser>[Chapters 5–6, robot kinematics and inverse kinematics; Chapter 12, contact modeling and equilibrium conditions]{ref} Its contact discussion makes another key distinction: deciding when to touch the environment changes the applicable physical constraints. A <roboticist> may consequently work with mechanisms, algorithms or experiments while still needing a common model of what is sensed, commanded and physically achieved.
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