feng@caen.engin.umich.edu (Liqiang Feng) (06/10/91)
Hi, I am looking for a device that will give me the orientation measurement of a mobile robot. Of course, the first thing comes into mind is the compass, however, the compass suffers from the the effects of external magnetic field and acceleration. Now I turn my attention to gyroscope, here the problem is the cost. Does anybody know any companies making some reasonably cheap gyroscope? I do not require very high accuracy, ~+-0.5 deg or even a little bit larger is fine, and also I do not require very small drift over time. Are there any other devices I could possibly use to get the orientation information. Thank you in advance.
newman@theory.TC.Cornell.EDU (Bill Newman) (06/10/91)
In article <00--VV-@engin.umich.edu> feng@caen.engin.umich.edu (Liqiang Feng) writes: >Hi, I am looking for a device that will give me the orientation measurement >of a mobile robot. Of course, the first thing comes into mind is the compass, >however, the compass suffers from the the effects of external magnetic >field and acceleration. Now I turn my attention to gyroscope, here the >problem is the cost. Does anybody know any companies making some reasonably >cheap gyroscope? I do not require very high accuracy, ~+-0.5 deg or even >a little bit larger is fine, and also I do not require very small drift >over time. Are there any other devices I could possibly use to get the >orientation information. > >Thank you in advance. _Radio_Electronics_ just ran an article on constructing an electronic compass using Hall effect sensors. The schematics seemed to me (a theoretical chemistry grad student with little practical experience) to have some errors, but the basic concept seems practical enough. Since the Hall effect sensors are solid state, this would eliminate any problems with acceleration; I don't know whether you could get +-.5 degree accuracy, though. Bill Newman newman@theory.tc.cornell.edu
smith@sndpit.enet.dec.com (Willie Smith) (06/10/91)
In article <00--VV-@engin.umich.edu>, feng@caen.engin.umich.edu (Liqiang Feng) writes... >Hi, I am looking for a device that will give me the orientation measurement >of a mobile robot. Of course, the first thing comes into mind is the compass, >however, the compass suffers from the the effects of external magnetic >field and acceleration. A Gyro would probably be pretty expensive, why not use a Flux Gate compass? Radio-Electronics had an article on interfacing the Radio Shack model about a year ago, or I've heard you can get them with RS-232 output from marine supply places for a few (three?) hundred bucks. You still have to worry about external field, but if you mount the sensor away from large pieces of metal and/or high-current wires, you should be OK. You don't have to worry about accelleration at all, as there are no moving parts (the meter movement doesn't count), and the best part is it only costs about $50 plus a couple of A/D channels and a little processing time. Willie Smith smith@sndpit.enet.dec.com smith%sndpit.enet.dec.com@decwrl.dec.com {Usenet!Backbone}!decwrl!sndpit.enet.dec.com!smith
tom@intran.UUCP (Tom B.) (06/13/91)
I have some experience with Magnetic Flux Gate compasses (about a year ago
Radio Electronics published how to modify the Car Compass for computers).
and I currently have the Dinsmore Device (4 hall effect transistors) in an
underwater robot. Also a student pilot.
The Compass and gyro should both be used together on land based robots.
Reasons:
a. Compass is affected by metalic objects in buildings, ground, etc.
b. Gyro's have a tendency to precess (drift) due to friction, and other
mechanical factors.
c. Compass can be used to "normalize" gyro inputs.
While flying an airplane, a pilot much reset the gyro to the magnetic compass
every 10-15 minutes. the Gyro is used for flying, but the compass is accurate.
The airplane must be in straight and level flight to use the magnetic compass
because in turns the compass will hang, lead, or follow the actual direction.
The gyro may also lead in a turn, or indicate opposite direction at the start of
a turn, but this maybe due to adverse yaw.
I hope this information is useful
Tom Brusehavermonty@sagpd1 (06/13/91)
In article <1293@sousa.ltn.dec.com> smith@sndpit.enet.dec.com (Willie Smith) writes: >>Hi, I am looking for a device that will give me the orientation measurement >>of a mobile robot. Of course, the first thing comes into mind is the compass, >>however, the compass suffers from the the effects of external magnetic >>field and acceleration. You might try looking in your local junk yard for the compass used in the dodge minivans. The overhead console has a compass/temperature read- out ( on the deluxe models). It only displays to the degree but possibly the guts are capable of more. Worth a look into anyway. Monty Saine