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View Full Version : InfraRed = gps ?

nzj1
10-01-2004, 23:16
one of the biggest things for your robot to do during the autonomous period is know where it is on the field and so if it gets off course it can make corrections to its path. I was wondering if you could use the
InfraRed as if it were a gps and triangulate its position on the field
Scooter
10-01-2004, 23:34
Absolutely....If you have a little steroscopic tracker like they had, you can calculate a vector to the emitter and a distance. This right here is enough to be able to tell your postition, but the farther away you are, the less accurate your distance mesaurements are. If you add a third detecor on top of one of the other two and have it slaved to the other emitter, then you can get pretty accurate location data. If you use some trig, you can derive a set of coordinates, and a location on the field.

Bill
mightywombat
11-01-2004, 00:02
how will you tell which emitter it is tracking though? they won't emit the same signals?
Michael Auchter
11-01-2004, 00:06
how will you tell which emitter it is tracking though? they won't emit the same signals?

well, they both operate at 40kHz, but each one of the emitters has a different pulse width.
GregT
11-01-2004, 00:12
how will you tell which emitter it is tracking though? they won't emit the same signals?

I'm pretty sure you will have to know the angle to both points to get your position on the field. Knowing the angle to one emitter will just give you your relative position to that emitter.

I attatched a image (after an hour of fighting with inventor). See if it helps you understand the geometry.

Greg

Geometry is definitally not one of my strong points, let me know if I'm wrong.
ahecht
11-01-2004, 00:18
Also, if you can't place the detectors far apart, you could have each detector track one of the two beacons.
Scooter
11-01-2004, 01:01
But if you know the position of that emitter, and your position relative to that, then it is easy to deduce your position relative to the field.

Bill
PhatalEphekt
11-01-2004, 02:33
yes, but it would be easier to judge direction with two sensors
jneumiller
11-01-2004, 11:12
yes, but it would be easier to judge direction with two sensors

I need to talk to my smart guys, but think that knowing just two points is going to be problematic. There are going to be issues with tolerances in distance measuring (provided I can do that with the sensors).

Check the sketch...see if this makes any sense.

Jim
Justin Stiltner
11-01-2004, 11:39
If you were only tracking one beacon, couldent your robot be anwhere on a circle scribed about that beacon with the radius of the 2 sides of the triangle formed from the sensors? IE you know how far away from the beacon, but unless you are using crab, or omni drive and can keep the orentation of your robot square in relation to the sides of the field... you cant really tell your exact feild position.... or is there something that im missing
Kevin Watson
11-01-2004, 12:40
how will you tell which emitter it is tracking though? they won't emit the same signals?Both emitters are sending out a 40KHz carrier frequency. The difference is that a "type-0" beacon has a 1ms envelope, while the "type-1" beacon has a 2ms envelope. The duration of the envelope is what determines the type of beacon.

-Kevin
mightywombat
11-01-2004, 12:44
ok. So you'd have one beacon tracking each of the different types by how often they recieve envelopes? How exactly are you going to figure out the distance from the emitter? Will the signal be recognizeably weaker the farther you get from it?
Stephanie
11-01-2004, 12:52
How exactly are you going to figure out the distance from the emitter? Will the signal be recognizeably weaker the farther you get from it?

your angular position wrt the other beacon will change.
Trig.
mightywombat
11-01-2004, 12:55
Ohhh. Boooo..... I don't like trig.
Kevin Watson
11-01-2004, 13:03
If you were only tracking one beacon, couldent your robot be anwhere on a circle scribed about that beacon with the radius of the 2 sides of the triangle formed from the sensors? IE you know how far away from the beacon, but unless you are using crab, or omni drive and can keep the orentation of your robot square in relation to the sides of the field... you cant really tell your exact feild position.... or is there something that im missingThe setup used at the kick-off demo allows you to calculate a heading and distance to the beacon. If you think of the beacon as the origin of a polar coordinate system, and you know the distance and angle to the origin, you should be able to figure out your position within the coordinate system. With a little trigonometry, you should be able to calculate a cartesian x,y solution too.

-Kevin
Kevin Watson
11-01-2004, 13:21
ok. So you'd have one beacon tracking each of the different types by how often they recieve envelopes? How exactly are you going to figure out the distance from the emitter? Will the signal be recognizeably weaker the farther you get from it?This is the sequence of events within the beacon state machine:

1) The type-0 beacon is allowed to flash for 1ms. As the carrier frequency is 40KHz, this means the LED will flash on and off 40 times.

2) A delay of 3.5ms where both LEDs are off. This allows reflections to die off before...

3) The type-1 beacon (on the other side of the field) is allowed to flash for 2ms, which means the LED will flash on and off 80 times.

4) Another 3.5ms delay is inserted where the LEDs aren't flashed before the state machine starts all over again at #1 above.

If you add up all of the periods (1ms + 3.5ms + 2ms +3.5ms), you'll see that the total time needed to flash the beacons is 10ms, which means the beacons flash at a 100Hz rate.

You can calculate your distance and angle to the beacon by using a little trig (exercise left to the student :)).

-Kevin
mightywombat
11-01-2004, 14:02
OK. That makes alot of sense and is actually pretty cool how it works. Thanks for explaining it.
Anthony Kesich
11-01-2004, 16:58
If you were only tracking one beacon, couldent your robot be anwhere on a circle scribed about that beacon with the radius of the 2 sides of the triangle formed from the sensors? IE you know how far away from the beacon, but unless you are using crab, or omni drive and can keep the orentation of your robot square in relation to the sides of the field... you cant really tell your exact feild position.... or is there something that im missing

Gyroscope with integration. Your programmer should be able to do this of he's/she's worth his/her beans. This way you know your angle relitave to the field and sdjust the trig respectively. All i know is triangulation is going to cost me a pretty penny in paper. Also, you can use the gyroscope in conjunction with some accelerometers to have a backup positioning system.