122 • A control rack containing signal conditioning for sensors, drive electronics for the X-Y stage  motors, and the control computer with its peripherals (not shown in Figure 2).  • Triangulated stiffening elements to stiffen the telescoping tower in yaw and roll (not shown in   Figure 2). These will be discussed in the Lesso ns Learned section. 

Operating Principles   At the heart of the WAGM is the pr oven AGM (Anti-Gravity Machine) te chnology. The AGM is essentially  a pressure-regulated air spring. It is shown schematically in Figure 3. 

Figure 3:  Operating principle of the AGM   The load is supported by force developed by an air pist on that moves vertically in a closely fitted cylinder.  The piston is of a special type that combines the functions of a piston and an air bearing. Air circuitry within the piston produces a very thin air film between the piston skirt and the cylinder wall, thus eliminating all friction while providing a force capacity equal to the piston area times the cylinder air pressure.  Figure 4 shows two detail views of the AGM. The pist on lifts against a moving carriage (shown in red) that  rides vertically on four conventional air journal bear ings that completely eliminate friction between the  frame and moving carriage. The volume below the pist on is pressurized with air by a precision manual  pressure regulator. For slow vertical motions of the pi ston, the pressure regulator vents air into or out of  the cylinder and buffer tank to keep the pressure cons tant. The buffer tank assists in this function by  reducing the effective stiffness of the air spring for sm all motions, even if they are rapid. The effective  stiffness of the air spring c an be reduced significantly by simply incr easing the size of the external volume  in the buffer tank. The tank also slows down the res ponse of the piston pressure when the regulator set  point is changed, thus making the device more trac table and easier to “dial in” to a desired pressure.   The lower end of the moving carriage connects to a cable-and-pulley motion amplifier. The amplifier allows the 45.7 cm (18 in) vertical stroke of the air cylinder to produce a 182.9 cm (72 in) vertical displacement at the end of the load cable attached to the payload. The cable-and-pulley motion amplifier  is required because the piston and cylinder of the AGM require extremely close dimensional tolerances to  function correctly. This limits the length of cylinder th at can be fabricated and hence the working stroke of  the AGM. Fortunately, the AGM has much greater fo rce capacity than needed for the application. In  general, the AGM force and stroke capabilities can be matched to the requirements of the load by using a  simple displacement multip lier composed of a load cabl e and three pulleys. The pr inciple is illustrated on  the right in Figure 5. In the interest of minimizing friction and wear in the cable, the pulley diameter is  about 80 times the diameter of the cable 2. 

                                                  2 The nominal standard for aircraft control cables is a minimum ratio of 35:1. PayloadBuffer tank Compressed air in LoadcableFrictionless PistonPressure regulatorCylinder NASA/CP-2010-216272