Can be found randomly spread out ewery where but moust comen locations to meet them are in skysryper or crank universe/demention x(light purple on mini map)
There are 4 types of crank droids
1.in black suits walking humans shooting purple laser (ewery where)
2.silver crouching cyborgs with blue shield shooting laser(skyscryper buiding/dark purple on minimap. Also in midle of sewers)
3.walking blue cyborgs shoting laser(found in sewers, in tunel conecting east and west sewers in the midle. Green on minimap are)
4.big fat robots shoting projectiles from ass(found in crankc universe/bright purple location on map in skys)
How you knock this achievment out is where you can go between the rooms and in bouth of them there are enemys you need. Kill them go in other room they respawn back in previous room. Go back and kill them again. Do that back and fowar and achievment is yours