More advanced than the Drophyd Sentry, the Drophyd Trooper enemies came equipped with an arm cannon which could fire from long range.
While they were not very strong, when multiple foes are grouped together, they could become a moderate threat.
Use the strafe maneuver and side flips to avoid their projectiles while nailing them with the Combuster from afar.
Elite Drophyd Trooper
Elite Drophyd Troopers were stronger versions of the Drophyd Troopers. They were found on planet Reepor and planet Fastoon. These enemies dealt more damage, could hover, and could enter stealth mode. 
Behind the scenes
Ratchet & Clank: Full Frontal Assault
Notes and references