[Help] Problems with Encoders and PID Control

[The Lucas]

Originally Posted by tStano

How would you use the voltmeter to tell whats wrong with the encoder? Just to see that it is indeed getting power and common? The pulses on the output channels will probably be much too fast to be read without an oscilliscope, unless the encoder has really low resolution I suppose. Carry on.

Many multimeters have a "Hz" setting that can be a quick check for encoder output channels, including this one that was offered in First Choice. Spin encoder by hand to test frequency of your outputs (faster spin = higher frequency).

Aaron,
As others have suggested, checking the voltage supplied to the encoder (as close as you can get the probe to the actual +5 pin on the encoder) is a good start. From some of the symptoms you describe, I suspect you may have a short on the 5v rail of your RoboRIO. There are several more convenient indicators (other than a voltmeter) that will tell you if a short has occurred. These indicators include Red Power Led on the RIO and the RoboRIO webdash. A limit switch does not require 5v power so it is not a good proxy for an encoder in a test.

If you do have a short, look for any obvious swarf (metal shavings) that could be causing it. If you can't find any foreign metal shorts, then it is time to unplug everything (one by one) from 5v until it goes away. Inspect the wire with the short to find the source. One of the sneakier causes of a short is the frame violating the insulation of those 3 wire cables.

I had a swarf short issue this year that took me a while to resolve the night before bag. Here is a brief summary (highlights on my mistakes) with some dead ends and hours of bot drive time removed. I first noticed the navX MXP board 3.3v LED was off. I removed the navX, expecting to find metal under the board (last time it was the 4-40 lock nut that holds the navX shield on ), but no short there. Grabbed the multimeter, the 3.3v pin on the MXP tested normal. Confused (I thought the navX used 3.3v input, it uses 5V), I eventually tested the 5V on the MXP. It was 0v, and I was wondering why the MXP 5v pin was not working but the rest of the RIO had 5v (I assumed, but it did not). I slowly connected a massive amount of swarf in the DIO ports (some perfectly coiled around 5v and ground) and then noticed the Red Power LED on the RIO. It is easy to develop tunnel vision when you think you know the cause of the issue, when you need to step back take a look at the bigger picture and test your assumptions along with basic fuctionality.