Apparatus (22) for controlling motion of an invasive probe (30) relative to a sheath (24) enclosing the probe (30). The apparatus (22) includes an outer casing (102), configured for connection to the sheath (24). The apparatus (22) further includes a drive mechanism (100), fixedly connected to the outer casing (102). The drive mechanism (100) has a first set of components, configured to translate the probe (30) along a direction parallel to an axis of the probe, in order to advance and retract the probe (30) with respect to the sheath (24) in a translational stepwise manner. The drive mechanism (100) also includes a second set of components, configured to rotate the probe (30) around the axis of the probe, in order to rotate the probe (30) clockwise and counter-clockwise, with respect to the sheath (24), in a rotational stepwise manner.
