IR & Sonar sensors precision

What is general distance and precision of hobby (low cost) IR and Sonar sensors. Which is best in terms of goodness/price? Thanks. Ek

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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...

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Thanks, Dale. Interesting how many sonars usually needed to cover 360 degree view.

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
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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
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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.

Earl Bollinger wrote:
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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.
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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.
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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.
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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

The Artist Formerly Known as Kap'n Salty wrote:
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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.

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.

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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.

Thanks again all!
What is resonable set of sensors for robot with 12"x12" size?
What would be your selection? Please be concrete if possible.

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>&nbsp;</P></DIV></BLOCKQUOTE></BODY></HTML>
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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>&nbsp;</P></DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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What about compass, wheel encoders? Are they a must?

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>&nbsp;</DIV></BLOCKQUOTE></BODY></HTML>
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Ek wrote:
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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.

in message
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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.)
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Is there any good link on mechanical part of the bumper? I want to start making it immediately :-)
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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.
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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 ===================