Anyways, im making a grappling gun. the way i want it to work is:
step 1: the gun fires an mosr
step 2: the mosr sets the closest unit (firer) as the actor
step 3: the mosr keeps flying forwards untell it hits a wall
step 4: it pins itself when it hits the wall
step 5: recoreds the current distance between the actor and itself
step 6: keeps that distance steady untell you stop fireing (ie, keeping you in a circle around you)
step 7: realse the fire key and you fall.

i know some basic lua:
ie, i know how to set variables, but how do you add forces and check for collisions? thats what i need too know. any help would be much apruciated.

This will help with step 4:
http://datarealms.com/wiki/index.php/Lu ... trengthRay

Darlos's climbing code has a good example, and so does lua tech's gravity hook.