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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Tue, 13 Jul 1999 18:26:28 GMT
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Original-From:
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Luis Villa <liv@duke.edu*avoidspam*>
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Viewed:
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971 times
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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 could be either the
result of slop (very likely) or rotation sensor loss (no way of telling.)
60 seconds per minute gives 39000 ticks per minute. Again, due to my
setup, there is no way of measuring this exactly- the arm is blocked by a
bar on either side and cannot do an actual full revolution, which is why
I counted by the second and extrapolate here.
16 counts to the revolution gives ~2440 rpm. If anyone wants to try to
better this, please let me know, whether it works or not.
Luis
P.S. Dave, I have no idea why you are wrong, but if you can think of it
(since you are more familiar with the hardware than I am) I'd also love
to know. Also, the suggestion to sense a +2/+1/-1/-2 has a basic problem,
since there is no way to distinquish between +2 and -2, so unless you
declare a directionality in the code beforehand, you are stuck.
On Wed, 7 Jul 1999, Luis Villa wrote:
> 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
>
> #######################################################################
>
> Profanity is the one language that all programmers understand.
> -Anonymous
>
> #######################################################################
> --
> Did you check the web site first?: http://www.crynwr.com/lego-robotics
>
>
#######################################################################
Profanity is the one language that all programmers understand.
-Anonymous
#######################################################################
--
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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| In article (...) 650 ticks per second works out to about 1.5 ms per tick. I didn't think the RCX sampled inputs that fast - I thought it was 3.0 ms per sample. If so, this would mean that the RCX is capable of adding 2 to the rotation value during a (...) (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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| (...) 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 (...) (25 years ago, 7-Jul-99, to lugnet.robotics)
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