Thread: LabVIEW Encoder not reliably returning Rate
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Unread 17-01-2011, 01:09
jhersh jhersh is offline
National Instruments
AKA: Joe Hershberger
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Re: LabVIEW Encoder not reliably returning Rate
Quote:
Originally Posted by apalrd View Post
Hello, all.

Yesterday, I was testing and tuning some code on a test chassis. It has two Toughboxes and US Digital encoders (from AndyMark, 250 count) connected to the last four digital inputs on the Digital Sidecar. In code, I found that Encoder Get does not reliably return Rate: I always get Distance (which I found to be accurate in both forward and reverse, by drawing a line on the wheel and reading the distance both ways. Only one of the encoders returns rate, though, which puzzles me. What puzzles me even more is that when I set the Decoding Type to 4x (Because that uses an FPGA Encoder instead of an FPGA Counter) it works - but only until I reboot (when the problem happens again, and is fixed by switching back to 1x).

I dug into the WPI Encoder Get to see if there was a bug there. WPI Counter Get is returning a time of Inf, which Encoder Get is scaling to 0. I went into WPI Counter Get, but that just talks to the FPGA (meaning I cannot dig deeper). When I first had the issue, I probed the Dev Refs and the non-working encoder was using Cntr 1 while the working encoder was using Cntr 0. I did not probe them using the 4x decoding, but when using 4x decoding, the other side (the one that worked before) now has the issue.

I am sure all of the hardware works. I swapped the encoder wires (Between encoders) and the problem is not the encoder itself. I also know that I am not missing the B-phase, because it counts forwards and backwards. Everything I have looked at points to a bug in the FPGA encoder handling, I am using the latest 2011 image. (I guess I could try the 2010 image to see if it works, but I won't have access to the robot until Monday).

Has anyone seen this issue? How did you solve it?
I'm really curious if the same issue reproduces in any other language. There have been a few issues with the encoder rates in the past, but I had thought we fixed them all.

Have you tried modifying the averaging settings? How does that setting impact the behavior? Is there any interaction between the 2 resources... i.e. if you make one encoder 4X and the other 2X, does it still do this?

Thanks,
-Joe

<edit>I assume you are using v25 since that is the only non-beta 2011 image</edit>
Last edited by jhersh : 17-01-2011 at 02:37. Reason: clarification
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