GravGen Cores are tightly compacted semi-solid Green Plasma.
planetside They are half-orbs attached to the underside of Trams where they are able to stop it's bulk from falling to gravity. Instead they are able to move straight across the ground, keeping a unmoving height from one point to another.
These Half Orbs are used primarily on Trams in the far north. They can keep the tram steady and give passengers a perfectly smooth flight across the Free Mountains even with the harsh winds slamming into the side of the Tram.
Two Half-Orb Gravgen Cores are required to keep a craft level, each 'remembering' it's height from the planets core and it stays at this height, these orbs themselves hold have no propulsion and instead Trams are pushed forward by multiple Orange Plasma engines
In Space they are large masses of Green cells in a complete orb held tight partially because of it's own mass, and partially because of a thin membrane surrounding it that continuously shoots out a stream of green plasma as a source of propulsion. It too can manipulate gravity a small amount but that is more for towing large objects.
GravGen orbs when being used to drag an object cannot be used for propulsion, Or else they might damage or shoot away the object they are dragging. This leaves the Robio to use its Orange Plasma engines to navigate. This however is slower and uses more Blue Plasma. Because of this, Robio crafts are rarely used for transporting objects this way.
The same idea can be used on smaller objects, these are called Grav Hooks. Grav Hooks are used by Drones to grip onto walls and to balance itself when walking. Some later Drones developed in the NomadLands can even easily walk on ceilings. On Robio crafts a large Gravhook is used on the center top Brace of the ship to grip onto the Gravgen Core and manipulate the GravGen Cores membrane, either increasing, decreasing it's propulsion or even closing off the Vein entirely. This opens up new smaller veins all over the GravGen Core but it no longer is used as a form of propulsion.