Encoders

[lafleur]

We have some question related to shaft encode support...

the reference below states that we can use 4 encoder at 4x speed:
what is 4x and 2x  and 1x relate too.. How fast the encode can turn with out the cRio missing a count? what is the max rate in 4x, 2x and 1x??

Is it 4 channel of quadrature A and B using 8 digital in allow for 4 encoders, or is it 4 digital in supporting only 2 encoders?

from FRC user guide:

"The FPGA on the CompactRIO device contains four quadrature decoders
that perform 4x decoding and eight decoders that perform 1x and
2x decoding to interpret the information the encoders return. The decoders
are not tied to a specific module or channel on the CompactRIO device.
You can reserve and release decoders as needed."

tom lafleur

team 812 mentor

[sciencewhiz]

The exact max rate for the encoders was posted both here and on the FIRST forums within the last few days. It's on the order of 10k pulses per second.

The 4x decoding is done by dedicated encoder hardware, while the 1x and 2x decoding is handled by the counter hardware (which can also be used by other things). There are 4 encoder and 8 counters in the hardware. Each uses 2 digital inputs.

4x decoding counts each transition on the A and B channels, thus a 64 tick encoder would give you 256 transitions. 2x decoding counts both transistions on 1 channel, and 1x decoding counts 1 transition on 1 channel.