Security and survival are two things hard to reach in land combat. Sometimes soldiers have to sacrifice their life just to hold a flat spot of land against hordes of enemies time enough for someone to be extracted by some spacecraft. Or stand against overwhelming odds, by clearing landing zones or protecting strategic places outmanned and outgunned.
So the Federation developed rock solid combat robots to deal with this kind of extreme situation, without loosing morale, surrendering or needing to be rescued or evacuated. The Hardpoint robot is a five-legs spider-like robot with the size of a small elephant, and can carry many different sets of guns, to combat vehicles, soldiers, flying ships or other treat.
Usually they are classified and equipped in five distinct ways, to perform different roles in combat. Against biological or small robots, they usually are fitted with gatling machineguns and grenade launchers, or a 3 barrels mortar pit (for long distance).
Against land vehicles and buildings (bunkers, towers, fortresses) they are usually equipped with a smaller version of the Artillery Mobile Base howitzer. For closer range they are equipped with an automated tank turret-like cannon.
For fights against airborne treats (either organic or starships) they can be equipped with an anti-air battery similar to the ones used at the Mobile Artillery Base [link]
The change of equipment must be performed at a base or ship, since they are too heavy for soldiers or smaller robots to carry and install.