Now stand by the chasm and wait for the beam to kick in and transport you across the pit. Now step out and look up for where the Cube dispenser is located. There's an L-shaped wall panel to your left, so place the transport beam portal here and hit the button. The Cube will drop down into the beam, so once it's resting up against the wall, look for the white square panel just up and to your right (it'll be facing you). Get the transport beam coming through here and it'll catch the Cube and bring it right over to you.