[Dprglist] straight lines

[Paul Bouchier]

David - going back to your description of how you manually turned the wheel
a little bit when the speed was supposed to be zero, and the integral of
speed error built up until it overpowered you and drove the wheel back to
where it started - I'm confused because I don't understand how you must be
calculating speed for that to be true. A naive implementation of
speed-measurement would be to count the number of encoder counts in each
40ms tick. So when you manually moved the wheel, let's imagine there were a
few ticks when a few counts were detected, then no more counts in any
subsequent ticks. Speed should be zero after motion stops, so where's the
error to integrate and cause corrective force to build up over time? Put
another way, there was a speed error a few seconds ago but now there's no
speed error; when does that error "go away", and when does the PID loop
stop remembering it and trying to fight against it?

This is relevant to my current concerns with Mowbot, since it was
discovered at Tuesday's meeting that the low rate of encoder ticks on
Mowbot means I'll only see 2 or 3 counts per tick (hard to control), so I'm
thinking about adopting Pat's approach (which he gave up on) of measuring
the period between count incrementing. Pat - I'm also wondering why you
gave up on that approach and changed encoders to one that has more counts -
was there some basic flaw in the approach?

Thanks

Paul
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