You can homebrew your own SONAR ( Polaroid ) using parts from an old
Polaroid, I got one for $15 on ebay. Here is a really cool link with
application code to OOPic:
http://www.robotprojects.com/sonar/sonarprj1.htm
have fun...
Hi
I don't know, as I am a newbie to it all...but if you look for the Polaroid
SONAR datasheet it will give the scan range ( Polaroid used to make just the
sensor ) that should help. Maybe you could mount it on a servo and oscillate
it?
Cheers
Dale
You best place I've found for old Polaroid cameras is in thrift stores. The
prices are typically in the $5-10 range (don't pay more than $10 - they're
not worth it) and you don't have to pay shipping charges.
~WEC
Basically the more you spend the better it gets.
Sonar generally has better range over IR, but sonar is sensitive to air
movement (such as wind).
Currently the small Devantech sonar range finders work out to about 6 feet
or 12 feet depending on the model.
But the sonar signal is cone shaped, so it gets larger the farther away it
gets, thus more than one object would reflect the sound wave back to the
receiver.
Usually you cannot get under 1 foot or so with sonar as with a single
transducer (acts as both speaker and microphone), you have pulse the output
sound wave out, wait a bit for the transducer to settle down, and then
listen for the return pulse. If you use two transducers, one to send one to
receive, you can get a little closer down to maybe 4 inches or so, but you
still have to blank the receiver to avoid noise from the transmitter.
IR on the other hand can work down to less than a inch away from something.
IR can usually get out to around 72 inches max range. But this depends on
the environment. IR interference from florescent lamps, sunlight, etc can
reduce or negate or jam out the IR sensors completely. Other IR sensors can
also interfere with one another was well. Now some guys have used IR
sensitive photdiodes with amplifiers and such and can get the range out to
50 feet or so, but this gets pretty advanced. IR sensors also have the same
problem with a IR signa; going out as a cone shape signal, thus more than
one object can be detected at longer ranges.
Both sonar and IR can have problems with some things like curtains or drapes
dampening the signal and not reflecting it back. Some objects like chair or
table legs can reflect little or no waves back causing the object to not be
detected until it's too late in some cases.
IR range sensors are more inexpensive as compared to ultrasound range
sensors, which are a lot cheaper versus laser rangefinders.
Another interesting sensor is the http://thereminvision.com/ object imaging
system, which does work pretty neat too, very sensitive to odd things like
chair and table legs and stuff..
Freescale semiconductor also has a MC33794 E-field imaging device, but it is
much less sensitive as it is intended for car seat passenger detection.
I should note that with the Devantech units, the minimum range is
actually down to around 2 cm or so. The wide cone and minimum range of
these units makes them excellent for obstacle detection. Other units,
such as those based on ther polaroid rangers have narrower cones and a
much larger minimum range (whichg can be lowered some as you mention).
The narrower cone of the latter makes them a bit more suitable for
mapping. I use the devantechs quite a bit and they work pretty well,
especially for obstacle detection and location.
Probably the best performing units for the money are the Sharp GPXXX
modules. They DO have a pretty narrow cone of detection which makes them
less than ideal for obstacle sensing (although I have used them as
"invisible whiskers" with some success).
Note also that sonar units (on multipel robots) can also interfere with
one another, but the effects at least for a couple of robots can
generally be mitigated somewhat in software.
The OP may consider using both in concert. A single Sharp unit combined
with a devantech sonar can do a pretty good job of both mapping AND
obstacle detection.
Has anyone actually used the thereminvision sensor on a working robot
yet? I have the unit, but haven't had a chance to play with it as of yet.
Cheers -- tAfkaks
--
(Replies: cleanse my address of the Mark of the Beast!)
Geez -- I really need to remember to spell check.
I forgot to mention that while the Sharp sensors perform reasonably
well, you do need to take care powering them if you intend to use more
than a couple, as they can induce a substantial amount of noise on the
power bus. While the current draw of these units is typically listed at
30ma, they actually flash the IR LED source at 1khz, with a 10% duty
cycle. When the LED is on, the unit draws around 300ma -- thus the 30ma
figure is actually an average.
--
(Replies: cleanse my address of the Mark of the Beast!)
Thanks all for reply. Good tips, pros and cons.
http://thereminvision.com looks very attractive with use of single numbers
of IR and sonars.
I am going to open another thread and ask if anybody was successful in using
thereminvision sonsors.
I am trying to assemble a robot similar to
http://oap.sourceforge.net/prototype.php .
One thing scares me that it uses 12 sonars that cost $360. Interesting if
Devantech sells them cheaper when purchased in bulk.
On the other side all sonars (in above project) are connected to I2C and do
not consume valuable analog inputs that is great solution. Is there a
project with schematic that connects IRs without consuming several I/O
lines?
Ek.
You might try the www.acroname.com site out for buying sensors. They were
pretty mnuch the first and have good doc's too for many items.
Another site is the www.junun.org site for sensors as well. these are sort
of the Portland Robotics people, and getting a nifty MarkIII robot is a good
deal too. It is a great way to get your feet wet.
One way to use a bunch or IR sensors is to use another MCU to handle the IR
sensors and query it using I2C or TTL serial, such as those found at the
http://www.al-williams.com/ PAKIII and PAKIV I/O processors. these work
well and are easy to hook up and use.
You are probably going to hate the answer, but it really depends on what you are going to do with it or use it for.
For example a line following robot would only need something to be able to determine whether it is on a line or not.
A robot that wanders around a room, maybe only needs bump sensors, or maybe some added IR sensors, and maybe a sonar rangefinder for longer distances.
Someone else may want to use the TheriminII sensors for up close object detection, and a scanning laser rangefinder for longer distances.
Somebody else like to use a CMUcam along with bump sensors.
Then someone else wants dual binocular TV cameras, radar, and GPS for outdoor work.
The first thing is to setup a set of mechanical bumper sensors, these are the primary and last resort if everything else fails to detect the object ahead.
Then maybe some IR sensors if you are indoors and IR interference from overhead lighting or sunlight isn't a problem. The TheriminII sensors would work well here too.
Next is longer distances, a sonar rangefinder would be a good starting point.
After you get that all to work OK you will have a good understanding of what you are really needing then.
Sounds like fun to me. :)
Good luck and happy roboting.
<DIV>
<P><FONT face=Verdana size=2>Thanks again all!</FONT></P>
<P><FONT face=Verdana size=2>What is resonable set of sensors for robot with
12"x12" size?</FONT></P>
<P><FONT face=Verdana size=2>What would be your selection? Please be concrete
if possible.</FONT></P>
<P> </P></DIV></BLOCKQUOTE></BODY></HTML>
------=
Conversely, I got expected introduction :-)
Your input is really valuable for me, communication and material for thinking.
Thanks.
Ek
<DIV>
<P><FONT face=Verdana size=2>Thanks again all!</FONT></P>
<P><FONT face=Verdana size=2>What is resonable set of sensors for robot with
12"x12" size?</FONT></P>
<P><FONT face=Verdana size=2>What would be your selection? Please be
concrete if possible.</FONT></P>
<P><FONT face=Arial
size=2></FONT> </P></DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
------=
A digital compass is tricky to use, it is very sensitive to metal in it's environment. Thus it typically has to be a away from the motors and things in a robot.
Then the office or home become a problem as the metal in some homes can interfere.
Some guys mount the compass on top of a boom or post above the robot a couple of feet. You also have to stop or pause and wait a few seconds before you can read it reliably. Basically the compass needle points to everything tht is metal or ferrous like tht gets too close. But then a nice screwdriver makes it easy to test directions. A good expensive serial interface GPS unit also gives you a heading or bearing too.
Wheel encoders, motor feedback "PID", quadrature encoders and decoders, are typically needed, but one can do things without them.
First they give you distance traveled for each driving wheel, you can then setup the robot to travel in a straight line, by adjusting the speed of one or the other motor. of course that means you are using PWM on the motor controllers to run the motors.
Your best bet is to buy a couple of nice DC gear motors with quadrature decoders already built in.
Some books to get and or read are "Building Robot Drive Trains", "Mobile Robots", "Robot Programming a Practical Guide to Behavior-based Robotics",
"Autonomous Mobile robots", "Computational Principles of Mobile Robotics", "Robotics and Automation Handbook"
Of course the Parallax Basic Stamp Robotics Manual and guide is excellent along with their other documentation.
A good starting point is Gordon McComb's "The Robot Builder's Bonanza", lots of good ideas in this book. :)
<DIV><FONT face=Verdana>What about compass, w</FONT><FONT face=Verdana>heel
encoders? </FONT><FONT face=Verdana>Are they a must?</FONT></DIV>
<DIV><FONT face=Verdana></FONT> </DIV></BLOCKQUOTE></BODY></HTML>
------=
You didn't mention the height, which is generally significant as well.
You also want to consider exactly waht you want the robot to do and
where you intend to operate it. But offhand I'd consider:
Motor stall sensing for when all else fails (though wheels will often
skid in the presence of obstacles rendering this useless)
A mechanical bumper. The more the area covered, the better. You do want
to be careful to design it so that it doesn't end up getting caught on
stuff and torn off of your robot. A single wrap-around piece is ideal.
I like the devantech sonar units for onstacle detection and limited
mapping. They have a relatively wide cone. At least two.
For longer range sonar mapping, a single polaroid sonar mounted on a
server works well.
There are lots of other possibilities, depending on what you want to do.
You can get a small wireless camera, temperature sensors, etc. Passive
IR sensors are easy to find (and cheap) to detect the presence of
(moving) humans or animals.
--
(Replies: cleanse my address of the Mark of the Beast!)
I think to minimize the height as much as possible down to 12inch.
Video camera (firewire) will be mounted on top or on regular stand attached
to the top (up to 20").
I have in mind a few applications, but first want to make a robot that maps
surrounding (inhouse) area and avoids obstacles, and manipulated through web
interface via wireless connection. It will have a charging station and
will carry tools (attached manually) one at a time for different purposes
(vacuum cleaner, electrical ant killer (do not laugh), etc.)
Is there any good link on mechanical part of the bumper? I want to start
making it immediately :-)
You know the height of the robot now, would you mind to give me an example
where you would locate sensors and their types based on the data available
from this thread?
I would like to have practical examples to start from. Every post/email is
very valuable for me;
I am collecting opinions to make a decision within short time.
more
the
at
30ma
The Sharp GP2xx units are nice, but they do have one drawback in that
they don't seem to be super reliable on a moving bot, or when scanned
on a servo turret/etc. This is related to the fact that they use
triangulation on the reflected beam, and average several results over
40 msec - IIRC, 20 samples or so. If the reflection changes
significantly over this period, then the readings can be fluke-y.
Some of this is discussed in the following appnote [I believe this is
the right one] ...
http://www.sharpsma.com/sma/products/opto/optical_systems.htm
Application Note: Distance Measuring Sensors
I'd be interested in hearing whether anyone else feels there is a
reliability problem when using these sensors on a moving bot.
- dan michaels
www.oricomtech.com
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