The Helium cube is a special type of chassis block in Robocraft. Helium cubes typically have high armor, directly comparable to normal armor blocks of the same tier, but slow your ship, have a high RP cost and a very high CPU cost in comparison. However, Helium, being "lighter than air," pulls the robot up with a bit of force at its location. The first tier is available at tier 4, formerly on the left side of the tech tree, now on the upper reigon next to the electroplated (around the full megabots update)
Compared to normal blocks of the same tier, Armored Helium blocks are very expensive. For example, the armored helium T4 block costs 12 CPU and 1354 RP, while the armored block of equal tier (Armored Cube T4) costs only 1 CPU and 235 RP. This makes building a helium-based ship costly. They also increase the Robot Ranking a considerable amount.
Unlike other chassis cubes, Helium blocks provide a certain amount of lift, measured in Newtons. They always lift the robot directly upwards, regardless of orientation, and do not require control input. With enough of them, the robot will lift up off the ground on its own accord; however, adding helium blocks will add a drag effect which slows down the robot while adding some stability. This makes them not an ideal choice for robots that also use aerofoils.
Helium blocks are designed to build slow flying, armed and armored ships. Unlike their agile, aerofoil-based counterparts, "Blimps" are much more stable, slow, and much less agile. However, because of the high armor value of Helium blocks, they are much more protected. A blimp will use Helium as its main block and source of power, while an airplane will rely on regular armor blocks, which weigh it down and thus are used sparingly. Airplanes rely on high speed to remmost as mobile when combined with Thrusters. Blimps also make nice and stable firing platforms for railguns or plasma cannons, resulting in an accurate sniper/bomber with an excellent firing angle.
Armored Helium blocks can also be used to make the bane of t1-5s: satellites. In the old days, we called them high-fliers. These bots are bots that float up to the "ceiling", or top of the map, and snipe people. Usually with rail cannons. Most satellites are mainly constructed with just a pilot seat, armored helium, and guns. Some more advanced satellites use electroplating for protection and thrusters for propulsion.