to make sure antagonists get stuck
The Robo-Grappler was a handheld device similar to the Ghost Rope. In essence a grappling rope, but instead of a person having to throw it so that it would catch on to something, this invention featured a tiny self propelled helicopter blade which would do the job itself. The Robo-Grappler flew towards it's target, dragging it's rope behind it and attch itself.
The Robo-Grappler was first used in the episode Maze Caves.