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Pneumatics are a type of mechanical device which provide motive power through the use of compressed air. They are related to hydraulics. LEGO have developed a comprehensive pneumatics system for use in Technic sets which this article discusses. For more information on pneumatics in general see Wikipedia:pneumatics


Pneumatic Elements

The pneumatic elements of LEGO Technic fall into three types:

  • Air providers, including a 48mm pump cylinder and 32mm compressor.
  • Air transmitters, including hoses, T-junctions, flex tubing, two-way switch valves and the air tank.
  • Air users, including 48mm cylinder and 32mm cylinder.

It is also possible to use a car tyre air compressor if you build an automatic pneumatic MOC that requires a lot of air (see MOCs below). Get the compressor with a pressure limiter on it and set the limiter to 20-25psi. Use above 30psi or long-term use above 25psi could damage your pneumatic elements and you do so at your own risk!

Pneumatic System Introduction

The system, as it is used in kits, is quite simple to learn and operate. Set the switch valve to the desired direction, press the pump cylinder a few times and the cylinder at the other end will operate a function. the Backhoe Loader set 8455 is a particularly good source of pneumatic elements, with two pump cylinders, seven switch valves and ten 48mm cylinders.

Extending the System

One set in particular has led Technic enthusiasts to build complex pneumatic systems. The set is the Crane Truck 8868. Its alternative model, a refuse truck, grabs an object in front of the cab, lifts it and drops it into the on-board container. This is a similar operation to the bar-code truck 8479, but it uses only pneumatics to do it. It does it by having a pneumatic cylinder push a switch valve lever at the same time as moving the arm mechanism. Another cylinder pushes another valve lever underneath the truck. The switch valves control each other's cylinders in a loop, which will keep doing the same sequence of movements whenever it is supplied with air. The pneumatic circuit for this is the equivalent of the electronic "Flip-Flop".

Extending this concept beyond the kits, the loop can be extended and equivalents of other electronic 'gates' can be created. Putting these building blocks together allows complex machines, known as Finite State Machines, to be created. Their applications are all kinds of pneumatic robots.

Pneumatic MOCs

This Pick-and-Place robot was created by Mark Bellis. It takes bricks from the chute and puts them in the bucket. There are four functions, with ten steps in the machine cycle. One function is done twice in each cycle. The circuit uses a Flip-Flop extended to three variables, the grab, wrist and elbow. An Exclusive-OR gate is used to make the arm extension move twice per cycle. The picture gallery includes a circuit diagram for those of you who would like to build a similar robot yourselves.

Many pneumatic walking robots have also been created (more info to follow).

External References