document: Analysis of exclusively kinetic two-link underactuated mechanical systems Analysis of exclusively kinetic two-link underactuated mechanical systems is undertaken . It is first shown that such systems are not full-state feedback linearizable around any equilibrium point . Also , the equilibrium points for which the system is small-time locally controllable -LRB- STLC -RRB- is at most a one-dimensional submanifold . A concept less restrictive than STLC , termed the small-time local output controllability -LRB- STLOC -RRB- is introduced , the satisfaction of which guarantees that a chosen configuration output can be controlled at its desired value . It is shown that the class of systems considered is STLOC , if the inertial coupling between the input and output is nonzero . Also , in such a case , the system is nonminimum phase . An example section illustrates all the results presented
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