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
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
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 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
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.
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
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
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.
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
I am trying to assemble a robot similar to
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
site out for buying sensors. They were
pretty mnuch the first and have good doc's too for many items.
Another site is the
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
PAKIII and PAKIV I/O processors. these work
well and are easy to hook up and use.
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] ...
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
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.
"The Artist Formerly Known as Kap'n Salty" wrote
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.