Yep, those pesky Halfmen created these robots that fire lasers at you
and are difficult to kill.  Here's how I did it easily:  Get a
good bow and arrow setup, if you have enough archery levels make sure
and get an AP (armor piercing) bow that has a long range.  When you
see or hear a robot, go hide behind a tree so he can't see you.  If
he's seen you he may already be shooting. Get out your bow and wait
until he shoots.  He will take a moment to reload, and in that time
you jump out from behind the tree and hit the R2 button which will make
him the target.  Jump back behind the tree and wait for him to fire
again.  When he's reloading, jump out again and fire an arrow,
jumping back behind the tree just in time to avoid his next shot. 
Keep doing this until he's dead. 
There are also a couple spots where you can stand on an overlook and
shoot the robots below using the "O" button to target them. 
Just wait, they'll all wander toward you and your bow.

Note, the "tree" method also works for other enemies later in
the game, and you can do it with rocks and boxes as cover as well.