  The configuration space of the mechanism of a planar robot is studied. We
consider a robot which has $n$ arms such that each arm is of length 1+1 and has
a rotational joint in the middle, and that the endpoint of the $k$-th arm is
fixed to $Re^{\frac{2(k-1)\pi}ni}$. Generically, the configuration space is
diffeomorphic to an orientable closed surface. Its genus is given by a
topological way and a Morse theoretical way. The homeomorphism types of it when
it is singular is also given.
