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Originally Posted by SlimBoJones
Alan,
We did exactly what you have done last year, but for different reasons. We haven't noticed the same kind of missing or phantom pulses as you've described, but last year we had only a 16 count/rev mechanical encoder handy, 0 days left to ship, and a wrist motor that needed to be limited and controlled in autonomous mode.
The 16 counts were not quite enough resolution, and gearing it was not possible due to weight and time, to get the positional accuracy we needed, so we interrupted on both the rising and falling edge, and reversed inc/dec behaviour based on the B-phase for the additional interrupts. It was a super quick and dirty way to get 2X the pulses from your encoder.
THIS year however, is a whole other story.
Not wanting to be left out in the cold again, we sourced some Grayhill 63R256s to place on our drivetrain and elsewhere. At low speeds, they performed wonderfully. Even at highspeeds, they performed wonderfully, without the 7474 signal stretcher...
But if you jerked, or bumped the robot - anything causing a momentary quick (albeit small) movement - we would often see pulses in the wrong direction, and the PID loop would compensate erroneously, sometimes causing runaway motors.
We built and installed the 7474 signal stretcher circuit, and it's cleaned everything up very nicely.
If it were my decision, regardless of your count rates, I would use the 7474. Your average count rates are one thing, but if EVER there is a situation that there will be a "bump" or other short, very fast movement where even two counts will come in very fast, then I would highly recommend the 7474.
-SlimBoJones...
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