I want to build a skydiving altimeter, which is a device with a pointer that looks like and is slightly bigger than a wrist watch. In this device I want to display altitude information using a pointer, again, in clock-like fashion.
It needs to have continuous and bi-directional rotation motion, so I'm initially discarding analog meters.
What type of motor fits the bill?
Best Answer
Digikey have (despite my prior suggestion au contraire) a large number of motors.
As an example only something like this MAY fit inside your spec - 24mm dia x about 12mm deep. Some what large as a "wristwatch".
Or you could lay this down with a right angle drive and hub drive of he "hand(s)".
About 16mm long and about 5mm across so you could fit inside an eg 20mm x 7 or so mm "watch" with suitable magic.
BUT
You could almost certainly build your own motor with less effort than you might expect.
A stepper motor type arrangement with a multi tooth disk and only two windings will allow unidirectional drive. Three windings and a toothed disk will allow you to make a basic stepper motor. You can add zero current hold in place with a permanent magnet if desired.
As Olin notes - it would be easier to implement something that LOOKED like what you have described but used a "sold state" display of some sort. Doing it mechanically is liable to be worthwhile only if you value the result for its artistic merits.