I'm starting to collect motors and getting more ideas for what to do with them. Most of them I have no idea what the characteristics are, so I'll have to experiment with them. This page and this page gives some useful information on how to test unknown motors. Testing methods include turning the motors at known RPMs and measuring current/voltage and running the motors at known voltage and current while measuring RPMs. To measure RPMs, I would have to build a tachometer. There's an Arduino-based test at Instructables. Preferably one that gives a nice output, e.g. with 7-segment LCDs. I just happen to have a bunch of those lying around, so why not test them all?
This is how my projects typically progress, or rather digress.
On with the testing. A cute way of testing can be found on Instructables, using only components that I already have (yay electronics conspiracy!)...
Or so I thought. Turns out my big mess of resistors did not in fact contain the required one. Now, at least my resistors are sorted so I don't spend an hour every time I start a project finding out that I don't have the resistor (except I haven't labelled them all yet for lack of good label).
Actually, I didn't have the resistors. Instead, I just took a larger resistor onto my breadboard, gave 5 V through it, and tried all combinations until a light went on. From then on, it was easy enough to map out the segments. All but one worked nicely.
Problem now is that it would require 7 pins per display to run it, or a driver (e.g. 4511) to decode and latch them. I don't have enough pins to drive more than one, and I have no 4511. So I can't use that for a display. Instead, I'll just read output on the Arduino, adding a potientometer if needs be.