Subject:
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Re: What is RPM of Gear Motor???
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 7 Jul 1999 11:50:57 GMT
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Original-From:
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Luis Villa <LIV@DUKE.nomorespamEDU>
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Viewed:
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833 times
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On Wed, 7 Jul 1999, Dave Baum wrote:
> My memory is a bit fuzzy here since it was a while back, but according to
> my notes...
>
> * sensors are sampled every 3ms
>
> * rotation sensor is a quadrature encoder with a 4:1 gearing in front of
> it (one rotation of the axle yields 16 "ticks").
>
> * sensor decoding software only handles +1/-1 tick. Opposite quadrant is
> ignored (more sophisticated software could assume 2 in the previous
> direction in this case, but Lego didn't think of that).
>
> In order to never miss a "tick", sensor would have to keep up with ticks.
> 3ms per tick means 333.33 ticks per second = 20,000 ticks per minute =
> 1250 rpm.
Oh! Math mistake on my part... 16 instead of 4. Hmm... the ~15K was an
off the top of the head estimate, which would go down to ~4K if divided
by four again like it should be :) I'll have exact numbers some time
today. Like I said, it is dropping some counts, and that may be as much a
sensor problem as it is a gear problem.
> This is all just theory, and could be wrong if I messed up on something
> like the sensor sampling frequency, etc. I do however remember having
> some trouble with the rotation sensor keeping up with 1750 rpm. I'll try
> to reproduce this again.
>
> Just curious - how are you getting 15,000 rpm - and what are you using it
> for? Most of my stuff requires lots of torque so I'm always gearing down,
> not up!
Well, like I said 75% of it is a math error (I strive to estimate nuclear
blast megatonnage by dropping paper, but I'm not quite there yet)... the
rest of it is consecutive gearing down from the large gears to the
smallest gears, three times. That gives me ~4K clicks of the rotation
sensors per complete armature revolution, which can take a very short
time. Again, I'll be doing the exact calculations for class notes
sometime today (should have been yesterday) and see what I get.
The purpose is to build a neural network based pole-balancing robot,
similar to any number of papers in the literature (I'll include a brief
bibliography when it works and I can describe it to the list.) Hopefully,
the code will be finished sometime today or tomorrow and then I'll have
to spend a little bit of time adjusting paramaters, so (knock on wood)
I'll have a description and post code friday.
Wish me luck-
Luis
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Profanity is the one language that all programmers understand.
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--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: What is RPM of Gear Motor???
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| Well, this took me a while, but it appears that the rotation sensor is reliably counting at nearly 2500 rpm. Here are the numbers: ~650 ticks per second. This count is not quite constant, but the error is within 5 percent. The way it is geared, this (...) (25 years ago, 13-Jul-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: What is RPM of Gear Motor???
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| My memory is a bit fuzzy here since it was a while back, but according to my notes... * sensors are sampled every 3ms * rotation sensor is a quadrature encoder with a 4:1 gearing in front of it (one rotation of the axle yields 16 "ticks"). * sensor (...) (25 years ago, 7-Jul-99, to lugnet.robotics)
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