Subject:
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Re: Precise turns of any angle! -- Rotation Sensor Information
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 13 Jan 2002 22:53:03 GMT
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Viewed:
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4529 times
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> I don't think so.
> The reason that count is lost is that the A/D conversion
> happens just in the moment when the sensor switches between
> two values, and you get neither of the two but the intermediate value
> on the other side of the cycle:
>
> 3
> / \
> 2 (2)
> | |
> (1) 1
> \ /
> 0
>
> Say you go from 1 to 3 and measure the ghost 2 in between.
> The ROM routine then doesn't change the count,
> and it sets the state to 2. The end result is a miscount by two.
> My experiments indicated a miscount for on the order of several
> thousand counts.
In 'The LEGO Lugger', previously posted at
http://www3.sympatico.ca/jdkalpin, the extended drive shafts for both sides
of a tracked vehicle, moving in opposite directions, are summed in a
differential with the difference (hopefully zero)fed to the rotation sensor.
Because the two motors are never the same there is always a very small
rotation, perhaps 0.2 rpm. At a count of '+2' the right motor is stopped
until the count drops to '1' and at '0' the left motor is stopped until the
count rises to '1'. The count is displayed on the RCX readout and the
vehicle is quite slow so you can watch it. A straight-line standard is the
joint in a tile floor.
My rotation sensor misses counts (and gains counts!) to the extent that I
cannot use it as a position sensor. This is probably not news to anyone.
The control system tracks beautifully but every three or four feet (of tile)
the count will drop to '0' or jump to '3'. Perhaps I can correct some of
this out by code that allows change of +/- 1 but filters out larger excursions.
My take on it is that the rotation counter is a good device when used within
its limitations and I should not expect it to be perfect. I believe I saw,
somewhere, a non-LEGO position sensor, a better bet for The LEGO Lugger.
Regards, Jerry
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