737 Duct pressure gauge

thingiverse

The pressure gauge for the 737 duct has two hands. Clearly, we will need two servos to drive these hands. Servos only turn 180 degrees, but the indicator scale spans about 270 degrees. Therefore, we will require some gears with a 180/270 ratio. A gear with 18 teeth on a 12-tooth gear will work. I built the entire mechanical system for the gauge using my 3D printer. I used cheap small SG90 servos. There are several parts to print. I designed all of this using SketchUp. The drawing shows most of the components. The brown-colored piece is what I call the base. The servos (light blue) are mounted on this base plate. On the servo shafts, I mount gears with 18 teeth. There are two different types of gears. The red gear on the picture has a short shaft, and the yellow gear has a long shaft. In the center, there are two gears with 12 teeth each. The green gear, with a long hollow axle, drives one of the hands. For the pink gear, I used a metal nail to go through the green stem and drive the other hand. In the center of the base plate, there is a hole. In that hole, I mounted a tapped M3 thread and screwed in a support for the inner axle (the nail). The top plate is not shown in this picture but is visible on the photo. On the top plate, there is a hole for the green axle. The actual scale will be glued to the top plate. The top plate is mounted on the base. I tapped M3 threads into the four outer stems to hold everything together. The two hands fit onto the green and the nail that is glued to the pink gear, going through the center of the green axle.