Subject:
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Re: rtlToronto11: Wrap up and Photo request
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Newsgroups:
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lugnet.org.ca.rtltoronto
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Date:
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Tue, 20 Aug 2002 15:32:48 GMT
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Viewed:
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720 times
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> the flag. I bet replacing one of you light sensors with a rotation sensor
> would have helped navigation a lot. In fact, I had an extra one and could
> have lent it to you, but didn't think about it until now.
This is what happens when you decide that the Grade 1 reading skills
were an unnecessary step in life...
When I was developing the robot earlier in the week, I built one of
the flags. Now, I knew it used the large Mindstorms wheel rim at one
end and the large pulley at the other, separated by the large axle, so
that's what I built. The light sensor was set up so that when the lift
arms were deployed, the sensor would be just above ground level. I
added the light to increase the effective range of the sensor. The
original design had the robot cross the bridge, turn toward the flag,
intentionally missing it by not turning enough and then move to within
20 cm of where the flag should be. It would then rotate
counterclockwise to look for the reflection off the rim and move to
pick it up. It was pretty effective*.
It wasn't until Friday evening that I saw the light....
Yes, I saw the picture of the flag on the RTL Rules page - Several
times.
Yes, the picture, as displayed, does have a tire on the rim.
Yes, I subconsciously chose not to see it.
Yes. I'm an idiot...
It wasn't until late, late Friday night (actually about 1am Saturday
morning) that I looked at the rules page one last time and FINALLY
noticed the tire. Needless to say, black rubber, a thin black axle and
a pulley viewed edge-on doesn't reflect light worth a damn. In the
event that the robot missed the flag (or was distracted by a light on
another robot) I needed two light sensors in front of the left and
right tracks for table edge detection so it could turn around and go
back. I figured it was better to navigate by getting a reading off the
target than to try judging my rotation** with only one rotation
sensor.
By the time I realized the true value of actually *reading* the rules
page (and paying attention to the pictures) it was too late to
redesign the robot for a rotation sensor. The light on the front just
ended up being for show. In hindsight, I wonder if I wouldn't have
been able to get a faster time without the extra battery box and
sensor.
Matthias Jetleb
* Pretty effective yes, but also pretty slow. This was my first
attempt at a tracked vehicle. The bridge I used was my original one
from the previous weekend that I had actually abandoned in favour of
something smoother. My original vehicle (wheeled) would get thrown off
course by the bumpiness of the bridge, even though the original had
twice as many axles to drive on. My problem was momentum. The easiest
folding bridge design opens up like a book, but needs some way of
being latched or it will collapse in the gap. I figured this would
make the bridge less reliable since it's natural tendency would be to
collapse unless you latched it, but the latch was a complication I was
trying to avoid. Unfolding it the way I did was self-latching (so to
speak) and incredibly strong. This method required lifting the whole
bridge in the air and the extra weight required to make the surface
smooth enough for wheels would either topple the robot or pull the
bridge from the robot's grip prematurely. The lightweight, sparse
design basically forced me to use either a tracked vehicle or build a
much larger robot.
** As everyone may have noticed by the jerkiness of the turns, the
track design doesn't work well on that table. I didn't expect that. It
turns much more smoothly on a bare wooden surface. Still, there is
considerable inconsistency in the rate slippage of the tracks as the
turn progresses. I therefore figured rotation sensors wouldn't do much
good since they don't measure slippage. If I had to do it all over
again, I'd go with a larger wheeled vehicle, a smoother bridge and
more counterbalance.
And I'd read the instructions completely.....
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Message is in Reply To:
 | | Re: rtlToronto11: Wrap up and Photo request
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| (...) I agree! The great thing about this event was that it was simple enough to attract many robot builders, but it was spectacular enough to entertain the croud. I especially liked the surprising outcomes like when Bruces robot reached the flag (...) (22 years ago, 20-Aug-02, to lugnet.org.ca.rtltoronto)
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