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Quadrature Encoders and VexNET
http://robotc.net/forums/viewtopic.php?f=11&t=1687
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Author:  kellyds [ Tue Apr 28, 2009 10:55 pm ]
Post subject:  Quadrature Encoders and VexNET

Howdy all,

I'm working with a local college team and we are running into a problem reading the quadrature encoder.

We are using the VexNET and running the debugger remotely. I was wondering if this could cause the interrupts on the encoder to be missed? What we are seeing is occasionally the encoder will count up/down, but more frequently we just see +2, 0, and -2 (or the value changing by those numbers). I test the exact same code on a Vex cabled directly to the controller and the encoders count up and down very well.

Finally, if it is interfering is it a case of the debugger being on or the a bigger problem with encoders and VexNet.

Thanks!
Sean

Author:  kellyds [ Wed Apr 29, 2009 11:47 pm ]
Post subject:  Re: Quadrature Encoders and VexNET

Not sure what we changed, but we replaced the Quad Encoder, twice and it seems to be working. Not sure if it's the cable or the encoder. Either way, it was not a problem with the wifi and the interrupts.

Sean

Author:  jbflot [ Fri May 08, 2009 11:05 am ]
Post subject:  Re: Quadrature Encoders and VexNET

Hi Sean -

Were you testing the same encoders remotely vs. directly? Some of the encoders have a manufacturing flaw. The following resource might be helpful: http://www.robotc.net/vex_full/reference/hp_check_quad.pdf

Author:  kellyds [ Fri May 08, 2009 1:20 pm ]
Post subject:  Re: Quadrature Encoders and VexNET

We observed the same behaviour with the encoders regardless of if it were remote (vexNet) or cabled. The problem is that we would do a test similar to what is described in the previous message's link. We did see the count increasing at the expected rate. Then we would attach the actual encoder to the frame it it would quit working. We finally got to the point where the encoders attached all were consistently counting.

It was almost as if it was ignoring either the interrupt input or the digital input. The signal would +-2 depending on the direction.

I'm still not clear as to what could be wrong, if anything, with the encoders. My gut feeling is that it's not the encoder, but rather the interface to RobotC or a configuration with the debugger or in the firmware.

When I get a chance I'm going to try to rangle up all the encoders that we were trying and then doing some more formalized testing of them. We've got a summer camp starting soon and I don't want to have to troubleshoot this specific problem during the camp.

I appreaciate the assistance and I'll post the results of what I find in a week or so.

Sean

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