This achievement is obtained by destroying 100 automata.
For information about the recycler machine, see the recycler page.
Master Recycler Achievement
The master version is obtained by killing 500 automata.
You can use any weapon, including bombs or exploders. Find a culvert, build yourself a little perch, and take 'em down as they spawn. Alternatively, you can vising one of several worlds with dedicated automata farms.
As with all mob-killing achievements, automata generated by spawners do NOT count.