Subject:
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Re: Rotational Sensor & Gearing Down
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 25 Jan 2001 22:04:57 GMT
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Original-From:
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John Barnes <barnes@sensors.(StopSpammers)com>
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Viewed:
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798 times
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>
> I'd *hope* not. If I were designing the RCX, I'd make the
> rotation sensor generate high priority interrupts so that
> sensors would be accurate no matter what...but who knows?
I just read the very interesting posting regarding testing the rotation sensor
to evaluate the "missing counts" phenomenon.
The above snippit would indicate that the rotation sensor is handled
differently from other sensors. It isn't!
It is sampled at the standard rate (one sample every 3 mS).
It's output is an "analog grey code" switching between four well known
voltages.
The software in the RCX must evaluate the rotation since the last sample
based on the change in this single analog signal.
Once the angular rate of the rotation sensor approaches one change every
3mS, all bets are off.
At low speed, there is a dither problem. The sensor output can be sampled
right at the edge of changing from one state to another. Since the connection
to the RCX is not particularly fast, there is a very real chance of catching a
reading from the sensor of a voltage which is bogus.
The only reason I know this is because I had to write code to handle this
sensor
for another hardware platform and thought I had problems with my code. At that
point I evaluated the RCX in detail and that is what I discovered.
Put a longish handcrank on a rotation sensor and wind it back and forth
from the
"edge" of one count to the "edge" of another. You'll pick up lots of
missing counts.
However:
I use rotation sensors to keep skid steer devices going straight with great
success;
Clear the rotation sensor channels first.
Run the motors using float commands to balance the counts.
Wait until the sum of the counts equates to the distance, appropriately
scaled, needed
to be travelled.
If you want to build a angular positioning servo system, use a small
potentiometer in a
brick and read it with the input port in passive mode. It works great! And
its absolute, so
there's no need to build a home mechanism. (I think there's reference to
this on Mike G's
page.)
JB
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Message has 1 Reply:
 | | Re: Rotational Sensor & Gearing Down
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| (...) Just don't go past it's Max or Min areas or you'll have a problem. This is probably a good place for the white slip gear... Dean -- Coin-Op's For Sale!: (URL) Lego Workshop: (URL) Lego Club: (URL) (23 years ago, 25-Jan-01, to lugnet.robotics)
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Message is in Reply To:
| | Re: Rotational Sensor & Gearing Down
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| "Bob Fay" <rfay@we.mediaone.net> wrote in message news:G7MKLo.2tB@lugnet.com... (...) I'll back that! It's totally hit-and-miss. I've done several tests on different gearings (some running the thing off a micromotor...) and no matter what, they (...) (23 years ago, 23-Jan-01, to lugnet.robotics)
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