<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<p>And another thing! (picture me with my right index finger raised
significantly, perhaps standing on a soap box)</p>
<p>I also have never had good success with magnetic compasses
indoors. Having said that, odometry is just a way of tracking the
robot's location, and their are other ways. We need a centimeter
accurate indoor GPS, or maybe something with radio beacons?<br>
</p>
<p>Karim, I have the same misgivings about robot contests. Mostly
because they tend to focus robot development on very artificial
environments, even though we tell ourselves that somehow these are
steps on the way toward more general purpose robots. In practice
the opposite seems to be true, that the contests year by year
produce more and more specialized robots that can only really run
the contest, and can't do anything else.<br>
</p>
<p>On the subject of the four corners calibration, you are correct
that the square doesn't have to be perfect or orthogonal or even
really a square. A rectangle will work. Or a large circle that
passes through the waypoints. Or even a circle that doesn't pass
through the waypoints. As long as the robot in total goes
through 360 degrees, clockwise or counter-clockwise, and stops at
what it thinks is the starting place.</p>
<p>I personally hope that DPRG does not go back to in person
RBNOs. I've enjoyed the virtual meetings and am not likely to
make the Tuesday evening gatherings at the Maker Space. Plus we'd
lose Murray, who probably won't drop by from New Zealand.<br>
</p>
cheers,<br>
dpa
<p><br>
</p>
<br>
<div class="moz-cite-prefix">On 05/18/2020 04:58 PM, Karim Virani
via DPRGlist wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAKtnkizFjKtBE81gaVrF_YrXUH4irrn6X07unYsu=2Gh3D7diw@mail.gmail.com">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<div dir="ltr">
<div dir="ltr">"Menacing lasers on robots? Hmm, yes", he said
stroking his white Persian,
<div><br>
</div>
<div>Since it looks like the subject is drifting faster than
my gyro, I'll quickly take one last whack at that dead
horse. I never meant to say you couldn't get positive
results with a magnetometer indoors. I've just reset my
expectations. I don't have carefully captured data to back
up my opinion, just anecdotal experiences. I probably tested
mems magnetometers in fewer than 15 different
venues/environments before giving up on that line of
inquiry. Again, I don't have hard data, but my impression is
that maybe 90% of the runs I did in those environments were
anomaly free. And a few of those environments were 100% free
in the specific paths where I ran robots. I just could never
predict where I would run into an anomaly or what the
consequences would be. When thinking toward robots that
should be able to reliably know where they are over extended
duration and without babysitting, it seemed to me I'd need
different orientation sensing. But those experiments did
have value for me.</div>
<div><br>
</div>
<div>On the subject of contests - I'm internally irritated by
them. Both by natural and philosophical leanings. I don't
get the FTW focus of spectator sports much either. But then
I come back around to remembering that I'm just an outlier
primate struggling to coordinate with his tribe. Contests do
provide the kind of goals and structure for progression that
my students can organize around. Without something like that
I'd lose the vast majority of them. It doesn't matter that
the goals are artificial and it's even essential that arenas
are protected from real world fuzziness. </div>
<div><br>
</div>
<div>Four square does benefit from good alignment to the
corner markers - though it's not actually necessary. As long
as your robot stays outside the corner markers as it
travels, it doesn't matter if the square your robot follows
is off a couple of degrees from the markers. It just matters
how close you end up to your starting point. This is a
training challenge for my students starting in middle
school. It is possible to scan with something as simple as a
wide beam ultrasonic sensor to find the angle to the first
marker. But that's because we used markers designed to give
a reliable signal on a smaller course. No such guarantee
with DPRG rules. The laser is a good bet.</div>
<div><br>
</div>
<div>Rounding up this grab bag of subjects, Texas has just
released new pandemic guidelines. Apparently youth clubs can
open today. I'm guessing DPRG doesn't qualify as that ....
But my team is discussing how soon their parents will start
letting them out of the house. We might start meeting on
Saturdays again soonish. With appropriate practices. If DPRG
starts in-person RBNOs again soon - please consider
including the remote component of our recent Tuesday nights.</div>
<div><br>
</div>
<div>Forever your most humble servant,</div>
<div><br>
</div>
<div>Karim</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, May 17, 2020 at
11:24 PM Murray Altheim via DPRGlist <<a
href="mailto:dprglist@lists.dprg.org"
moz-do-not-send="true">dprglist@lists.dprg.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">Hi Doug,<br>
<br>
Thanks for the info on the smaller LiDAR and the YouTube
video, which I just<br>
watched. If I'm trying to measure distance, the Benewake
products look really<br>
good, especially that smaller one.<br>
<br>
The idea of measuring a gap was a possible approach to
aiming at the first<br>
target of the four square challenge. It'd be kinda cool to
have the robot be<br>
able to locate that gap at the beginning of the course
rather than rely on<br>
the robot's owner physically aiming it at the target, but
either works: I<br>
like the complexity of the LiDAR and the simplicity of the
laser pointer.<br>
Hacking a laser distance meter might work but it's pretty
big physically for<br>
my somewhat-small robot. By contrast, the tactical red dot
laser I've just<br>
ordered from somewhere in China is 42mm x 20mm x 24mm and
weighs 28g. That's<br>
small enough to bury under my robot's bumper. For the same
price (US$13.55)<br>
I had the choice of a class 2 or class "IIIa" ("less than
5mW") laser and<br>
bought the more powerful one, which might be in the
cat-tattooing power range.<br>
<br>
Currently I've got that little Pimoroni VLX53L1X Breakout
Garden sensor with<br>
a range of up to 4m (though it seems more like 2.5m in
practice, really) and<br>
is about the size of a postage stamp (remember them?!). I've
mounted it on a<br>
micro servo and have a draft post on my blog that I've not
finished yet;<br>
suffice it to say that it's a very capable sensor and can do
an accurate 90°<br>
sweep in about 3 seconds. The power requirements are almost
inconsequential.<br>
<br>
David was asking me about it on our last video conference.
If you mount an<br>
ultrasonic sensor on a servo and try sweeping it that
quickly you get nothing,<br>
sound can't travel that fast, but the little laser works
really well (though<br>
yeah, the speed of light ain't what it used to be).<br>
<br>
Another idea I had was to use one of the Raspberry Pi
cameras to look forward<br>
towards the target and locate some specifically-colored
pixels. The resolution<br>
on the cameras is probably high enough that this might work
if the lighting<br>
in the room is good enough. Or, aim the camera at some kind
of point light<br>
source. The rules permit something like that.<br>
<br>
But if I'm not trying to measure distance, simply point at
something as a<br>
target, a small tactical red dot laser (with allen screws to
adjust trajectory)<br>
is just the thing.<br>
<br>
I appreciate the point of conversations like this is to
"advance the technology"<br>
that could be used on our robots. So using a LiDAR rather
than a cheap laser<br>
pointer would be a greater advance and a more interesting
experiment. So I'll<br>
continue to think about this (even though I've got a
menacing black laser on<br>
its way in the mail).<br>
<br>
Cheers,<br>
<br>
Murray<br>
<br>
On 18/05/20 2:57 pm, Doug Paradis wrote:<br>
> Murray,<br>
> I don't know what size gap you are trying to detect
or the speed that> the gap may appear. Hhowever if the
sampling rate is slow, about once > per second, another
possibility is a laser distance meter with a serial>
port. You can get a <br>
laser distance meter board with a serial port from>
Aliexpress (I have seen them listed, but can't seem to find
the right> search terms, so no link), or you might look
at this project<br>
> (<a
href="https://hackaday.com/2014/03/29/hacking-a-laser-tape-measure-in-3-easy-steps/"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://hackaday.com/2014/03/29/hacking-a-laser-tape-measure-in-3-easy-steps/</a>).
> I own one of these meters, have brought the serial port
out, and played> with it. Its cool, but a robot generally
needs a faster update rate.<br>
><br>
> Regards,<br>
> Doug P.<br>
...........................................................................<br>
Murray Altheim <murray18 at altheim dot com>
= = ===<br>
<a href="http://www.altheim.com/murray/" rel="noreferrer"
target="_blank" moz-do-not-send="true">http://www.altheim.com/murray/</a>
=== ===<br>
= = ===<br>
In the evening<br>
The rice leaves in the garden<br>
Rustle in the autumn wind<br>
That blows through my reed hut.<br>
-- Minamoto no Tsunenobu<br>
<br>
_______________________________________________<br>
DPRGlist mailing list<br>
<a href="mailto:DPRGlist@lists.dprg.org" target="_blank"
moz-do-not-send="true">DPRGlist@lists.dprg.org</a><br>
<a
href="http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org</a><br>
</blockquote>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
DPRGlist mailing list
<a class="moz-txt-link-abbreviated" href="mailto:DPRGlist@lists.dprg.org">DPRGlist@lists.dprg.org</a>
<a class="moz-txt-link-freetext" href="http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org">http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org</a>
</pre>
</blockquote>
<br>
</body>
</html>