Hi ozrien,
We use Vex shaft encoders.
http://www.vexrobotics.com/276-2156.html
To test the encoder, we fired up our test robot (uses a cRio) and got valid values from it when turning it by hand. I wasn't surprised by this because if we try 3 encoders and none of them work there is very little chance they are all bad.
Next, today's session, I will try it again on our current robot. If it works then the encoder is intermittent possibly due to wiring issues (see below).
If it doesn't, we will write a test program for it that tests only the encoder. The best case scenario is that it is our software bug because that will be the easiest to find and fix.
If none of this works on the roboRio, how do we test if we are getting output to the digital pins? Can that be done with a volt meter? If we don't see any with our simple program then what? That would seem a fairly serious problem with the hardware. If the roboRio is compromised, we don't have another.
Secondly, we use these adapter cable for the encoder. I hate doing it this way and I really wish the encoder came with female ends. This gives multiple points of failure. If these are intermittent they could even be our problem. The alternative is to cut and solder microwires and we've always avoided this. We went all last year with this setup with no problem but it is still worrisome.
http://www.vexrobotics.com/vex/produ.../276-2395.html
In any case I will report back what we find.