Simply put, capture a droid three (3) times. It does not have to be all three (3) that are available (A, B, and C), at one time. You only have to CAPTURE - the definition of
capture is to activate the droid - a droid (can be the same one) three times in the same play-through. For it to be the same one, obviously, the other side will have to re-capture it. To activate it, use
on the droid.
Relatively easy achievement. Best strategy i found - active a droid and run to the next one. By the time you get to the next one, there is going to be an opposing team member trying to re-capture the last droid you activated. There is also an award you receive for capturing three droids - in game, extra points. Rinse, repeat, and have fun ;D