First, you will need to get the Ragnarok DG-4. To do so, you need 3 parts.
Part 1: Dropped by a Panzersoldat, after you kill him. (he usually shows up in round 12-13)
Part 2: Put on the Death Ray (electrical floor trap). When the trap stops working, look into the air to see where a blue part has spawned. Then use one of the 4 wunderspheres to pick the part up. Depending on where the part spawns, you will have to decide which wundersphere you must take.
Part 3: Go to the Rocket Pad (by using the teleporter, which is located in the same area as the pyramid and the BRM). Wait until the rocket starts launching, then activate a located underneath the rocket pad (located on ground level, next to some stairs leading to the platform with the rocket and the location for the Pack a Punch machine). Now quickly head back to the Teleporter. You will see 3 lights on the left side of the teleporter. Wait until all of them are green and then hold
to activate the console. You will see the last part laying in the teleporter.
Now go to one of the workbenches located across the map and craft the Ragnarok DG-4 (and pick it up).
Now wait for another Panzersoldat to spawn. He should appear every 5 rounds after he appeared for the first time.
Press
+
at the same time to hold the Ragnarok DG-4 in your hands. Then you can press
to put the anti-gravity trap down. Put the anti-gravity trap down while you are near the panzersoldat, and then start shooting at him until he dies. You might be better off by first damaging the panzer a little, and then using the anti-gravity trap, since it will be easier this way to kill him while he is trapped.