737 Duct pressure gauge

thingiverse

The 737 Duct pressure gauge has 2 hands. Obvious we will need 2 servo’s to drive the hands. Servo’s only turn 180 degrees but the indicator scale is about 270 degrees. So we will need some gears with a 180/270 ratio. (18 on 12 gear teeth) I made the entire mechanics of the gauge with my 3d printer. I used these cheap small SG90 servo’s. There are several parts to print I designed all this using SketchUp. Pictures say more than words. The drawing shows most of the elements. The brown coloured is what I call the base. The servo’s (light blue) are mounted on this base plate. On the servo’s shaft I mount a gears with 18 teeth. There are 2 different gears. The red gear on the picture has a short shaft and the yellow gear a long shaft. In the centre there are 2 gears with 12 teeth each. The green gear, with a long hollow axel, will drive 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 centre of the base plate there is a hole. In that hole a tapped m3 thread and mounted a screw to support the inner axel (the nail) The top plate is not shown in this picture but you can see it on the photo. In the the top plate there is a hole for the green axel. The actual scale will be glued to the top plate. The top plate is mounted on the base. I tapped m3 thread in the 4 outer stems to mount all together The 2 hands will fit one on the green other on the nail that is glued to the pink gear, going through centre of the green axel.