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Sensors and Control

Hi all, (sorry about the bombardment of emails...)

I've been thinking about sensory systems and control (well, it IS my job). 
And here's what swirling in my head at the moment: 

1) Infrared Sensors

After surfing on the net for 2 hours, I think I have a better idea of how
IR detectors work.  IR sensory systems consist of 2 parts -- the emitter
and the detector.  The emitter is usually an LED and the detector can be a
photodiode or phototransistor.  The IR sensory model the Seattle Robotics
Society (SRS) people talked about gives a DIGITAL output.  However, I
don't know whether this is true for other models.  I figure that using a
photodiode (like in those dreaded physics labs) probably means that you
can get an analogue type input, so maybe we can somehow keep the analogue
characteristic of the signal. 

2) Multiple Sensors (for beacon) 

It would be nice to have multiple sensors so even if our robot can't "see" 
the enemy, it still has another sense to rely on.  However, I cannot come
up with any good/feasible secondary sensory mechanism at the moment. I am
tentatively ruling out sound due to the nature of sound wave propagation. 
It will be difficult to determine which direction the sound is coming
from.  I suppose we could mount a couple of "ears" around the robot and
compare the intensity of the signal received by each "ear" and then go
towards that direction.  Again, this would involve analogue->digital

Ultrasonic sensors are typically used as sonar to get more info about the
robot's surrounding (ie as a lookahead type sensor).  I didn't come across
anything about using ultrasonic signals the way we will use them (as a
beacon) if we do choose to use them. 

3) Radio Signals

I wonder maybe radio waves can be used as a 2ndary source.  It has the
same problem as sound waves (in terms of propagation <i think>), but they
can be made unique (like cordless phones). However, I don't know if this
is actually feasible.  (I'm wondering whether looking at signals emitted
by a cordless phone can actually tell you where the phone is... my
intuition says no... but I really don't know). 

4) Problem of Reflected Signals

(see the next email... this email is getting too long) 

5) Motor Speed Control

Some of the SRS webpages mentioned that it is possible to detect the speed
(&even direction) of the wheels (& hence the robot) using something called
an optic pair.  I neglected to look up what an optic pair is, but I think
it involves some sort of infrared sensor.  However, the optic pair was
only used on wheels that are not controlled.  I don't think our robot
actually needs this.  Implementation of this proverbial optic pair will
definitely complicate matters. 

OK. Now go on and read about my take on reflected signals. 

Joyce :)