Yay for pretty pictures! Um, wow. Just looked at tape altimeters and ,JEEZ, thats some amount of gears. Not a bother though if you have modern motors and Micro-controllers. Have you considered just going with the roller-disc-thing ones? Depending on the range and number size it might be quite big, but may be easier to make and less fragile? My god those navballs are sexy. Someone actually picked one up at an auction, what a lucky dude. Looking at your earlier picture, this might be a fun little project for me to investigate, any comments on that? Just looking for any info on the Gemini FDAI equivalent. Barely anything on it. All I know is it had 4 gimbals to avoid gimbal-lock and that it was used in Gemini.