[notmattlythgoe]

Originally Posted by Ether

Your S4 is less than half the CPR of the OP's and has ball bearings. So the two are not comparable. What works for you won't necessarily work for the OP.

At 7K RPM you are exceeding the speed the FPGA could handle if your S4 were at max tolerance for quadrature phase error:

Welcome to RLaB. New users type `help INTRO'
RLaB version 2.1.05 Copyright (C) 1992-97 Ian Searle
RLaB comes with ABSOLUTELY NO WARRANTY; for details type `help warranty'
This is free software, and you are welcome to redistribute it under
certain conditions; type `help conditions' for details
>
> format(5);
>
> CPR = 120 # cycles per rev (single channel)
      120
>
> EPRS = 2*CPR # edges per rev (single channel)
      240
>
> EPRQ = 2*EPRS # edges per rev quadrature (both channels)
      480
>
> RPEQ = 1/EPRQ # angular distance (revs) between cross-channel edges
0.0020833
>
> per = 261/40e6 # FPGA sampling period, seconds
6.525e-006
>
> RPS = RPEQ/per # maximum revs per sec
   319.28
>
> RPM = RPS*60 # maximum RPM (revs per minute)
    19157
>
> # angular distance (revs) between cross-channel edges
> # with "typical" tolerance:
>
> RPEQ_TYP = (90-10)/90*RPEQ
0.0018519
>
> RPM_TYP = RPEQ_TYP/per*60
    17029
>
>
> # angular distance (revs) between cross-channel edges with "max" tolerance:
>
> RPEQ_MAX = (90-60)/90*RPEQ
0.00069444
>
> RPM_MAX = RPEQ_MAX/per*60
   6385.7
>
>
> # RPM with no tolerance, typical tolerance, and max tolerance:
> RPM
    19157
> RPM_TYP
    17029
> RPM_MAX
   6385.7
>
>

After thinking about it more we weren't at 7k rpm the encoder was reporting a rate of 7k.