I am also trying to apply a torsion spring to a fixed point and floating point. How do you setup the mechanism in order to see the torsion spring react?
you crate a join between the two parts that has a rotational degree of freedom (ie pin joint). Then you add an spring to that rotational degree of freedom axis. Since that axis can rotate it becomes automatically a torsional spring. You could o a point to point torsional spring but most of the times you will use a join spring.