I noticed on a previous post by Aleksandar the use of RFID for
recalibration of a positioning solution based on accelerometers.
I do not have experience with RFIDs and i do not know the "distance
resolution" that the AGC stage of an RFID receiver can offer
(pressumably the fine tuning of location is done by measuring the signal
strength from at least 3 tags). If one is interested in rough
positioning of the kind "I know that my robot is now in room 117C" it
seems OK, BUT if one is interested in laying down RFIDs in known
positions (probably obtained with GPS) and then having the robot to
recalibrate itself once it meets one of the tags (to account for "swell"
or any other accumulative errors of an inertial navigation system) then
this solution is not a serious candidate. I suspect that the RFID tag
can be sensed (as a hard decision like YES / NO) within a circle of
radius R which introduces a serious error when positioning is performed
in small spaces.
As far as accelerometers are concerned, i found a very nice (although a
bit bulky) project that uses 6 accelerometers for a strapdown inertial
navigation system. You can find it here:
With sources about the sensors as well.
Also, STMicroelectronics is manufacturing three axis accelerometers in a
single chip (2g-6g range) with analog and digital outputs that are
capable of detecting even static gravitational fields (like earths
gravitational field for example). More about it here:
So theoritically, 6 DOF sensing can be done with two ST accelerometers
(one for sensing linear acceleration and one 3 axis linear accelerometer
for sensing tilt) tightly packed together and mounted on the robot...Any
chance of having these on an AcceliStix? :-)
All the best.
From: Jeremy Grosser <jeremy@ru...> - 2005-07-10 13:16:52
Those STMicroelectronics accelerometers look really nice. The digital
output model has an I2C interface so it should be able to hook right up
to a gumstix. Digi-Key has it for $19.25 at single unit quantities. I
might pick a couple up if I have any money left for this project after
the CF WiFi card.
Digi-Key Part Number 497-4129-ND
Manufacturer Part Number LIS3L02DQ
Speaking of which, does anybody know where I can get a CF WiFi card that
will work with the gumstix for less than $85? These cards are somewhat
difficult to find in my area so I'll have to buy it online.
From: Jeremy Grosser <jeremy@ru...> - 2005-07-10 14:18:24
Nevermind on the CF WiFi card, I found one on TigerDirect for $20 and it
has a Prism chip supported by linux-wlan-ng.
Belkin Wireless PDA Network Card (B20-5132)