Last game I ran I had an encounter featuring two Gearsman Robots (Inner Sea Bestiary pg. 94) up against my Lvl 3 Party consisting of 6 members, a brawler, a bard (archaeologist), a magus (kensai), a vitalist (Adv. Psionics), a wizard (spellslinger), and a Paladin (Holy Warrior of Light). This ended up as one of the more challenging encounters of the game as the Gearsman would deal significant damage and their hardness 10 would take most of the party's damage.
Long story later, anyone have recommendations on how the party should prepare for the return of these monsters?
I just ran an encounter of the same ilk with my own players: 2 constructs, Hardness 10, level 3 PCs. What I learned is: making the constructs single-minded (ie: bad at tactics) and clumsy really helped. But still, I should have probably just dumped the hardness to 5 and been done with it.
This would be a good starting place.
Abraham weapon blanch works against Damage Reduction but robots have Hardness.