Subject:
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Re: Help with my robot
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 12 Dec 2000 15:25:48 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail.netSTOPSPAMMERS>
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Viewed:
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774 times
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Ahui Herrera wrote:
>
> I got a problem. I have a simple two motor robot that I want to have a push
> button cause the following:
>
> 1 hit the push button
> 2 robot turns 180 deg and move forward
> 3. after 15 feet robot stops
> 4 repeat 1 - 3
>
> The problme i am having is that the robot will not go straigt. it is not
> turning 180 degrees.
As lots of other people have said - you really need rotation sensors.
If you don't have one - then a line-follower is an option (as other
people have also suggested)...or I *suppose* you could put a bright light
at either end of your 15 foot track and have the robot aim for the brightest
light source after it's done an approximate 180 turn. If you go this way,
you'll want the smallest (but brightest) light you can find.
But to do this properly - you'd certainly be better off with rotation
sensors - if you can do this - you should.
I suppose you could try to make your own rotation sensor by taping
a black/white strip of paper around a large wheel and use the light
sensor to count the number of stripes that go by. This scheme makes
detecting the DIRECTION of travel rather difficult though (not
impossible though - we can talk some more if you want to go this
way).
However, in your case, we don't need a full-blown rotation sensor.
For steering, you could arrange to have just one narrow black strip
on the detector wheel and use a differential connected to the two drive
wheels to rotate our detector wheel. Then, when the robot is going
straight, the black mark will remain under the light sensor. If the
robot veers off to the left or right, the black stripe will no longer
be under the light sensor. Unfortunately, you won't know whether to
turn left or right to correct for this - so you may have to turn left
for a little while - and if you don't see the black stripe, turn right
until you see it. The software to do that turns out to be IDENTICAL
to the code for a line-following robot!
In a sense, the robot is following a line that it carries along with it!
You could use the same technique to turn 180 degrees accurately by
arranging the gearing such that the detector wheels does an exact
whole number of rotations after a 180 turn. Then all your software
would need to be would be:
* If the bump sensor hits, turn for X seconds...which should
be approximately right for a 180 degree turn.
* Now, if we got it right, the black strip on the detector
wheel will be under the light sensor again.
* Run a line-following algorithm until the bump sensor
hits again.
Your description of the problem said you had to drive 15 feet.
That's rather hard to measure when you are doing 'line following'
because the robot has to stop frequently to find the line again,
and when you do that, you tend to lose track of distance travelled.
However, if what you really mean is to run until you hit the bump
sensor again (which happens to be a distance of 15 feet) then
what I suggest could work.
Good Luck!
---
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message has 2 Replies:
 | | Re: Help with my robot
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| (...) I thought in the same direction. For driving straight you don't need a light sensor (but for accurate turning) It must work with two touchsensors that were touched from an arm placed on the "detector-wheel". So you are able to detect to which (...) (24 years ago, 14-Dec-00, to lugnet.robotics)
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Message is in Reply To:
| | Help with my robot
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| I got a problem. I have a simple two motor robot that I want to have a push button cause the following: 1 hit the push button 2 robot turns 180 deg and move forward 3. after 15 feet robot stops 4 repeat 1 - 3 The problme i am having is that the (...) (24 years ago, 12-Dec-00, to lugnet.robotics)
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