Rescued from my old blog, a post about a Lego robot I was building ten years before...
This is an overall view of the incomplete robot, which has an anti-collision bumper, a compressor, air tanks, a pressure limiter, and computer operated pneumatic switches to control the air-flow to the pneumatic rams that were to operate a grabber arm. The arm was never built, and I wish I had time to do things like this now I don't even have a job.
Here's a close-up of the compressor, which has two pump cylinders for greater flow. I experimented with four, but the motor was getting a bit unhappy with the load on it, and two gave plenty of air.
Once the pressure in the reservoirs is high enough, this unit shuts off the pump. When the pressure drops, it switches back on.
This bit is particularly nifty. I used a single motor to operate two pneumatic switches each controlling a pneumatic ram. When the motor runs forward it operates one switch, and when it runs backwards it operates the other one.
This is a better shot of the twin pneumatic controller, which has another pneumatic switch on the other side. I used a shock absorber as a push-rod, as then I didn't have to worry about getting the stroke length exactly right. Hiding just above the pneumatic switch is a touch sensor whose purpose is to detect when the switch returns to the central position, after a blast of air has been sent to the ram.