[Robotgroup] Drive a Droid proposal... How to detect the "fence"?

[Clendon Gibson]

You don't have to do triangulation with the RF signal to figure out direction. If you have two antennas of the same shape, then the one with the weaker signal is 'away' from the wire. Barring complexities like signal reflection. 

If you want to get fancy, you can turn the robot until one antenna signal is maximized and the other minimized. This will give you a rough idea of facing. 

I think the gaffer tape idea is better, but you don't need a camera and this makes it more complicated anyway. Use some LED/Photo Diode pairs. The LED shines the light on the floor. The photo diode either sees the reflection or not. It's the difference between image processing and reading a few logic lines. (Tip: use more then one LED/Photo Diode pair at each point. Redundancy, and more light to sense.)

I think the most appropriate method would be to use the Force.



----- Original Message ----
From: Vern Graner <vern at txis.com>
To: The Robot Group Mailing List <robotgroup at puremagic.com>
Sent: Monday, July 7, 2008 9:01:11 PM
Subject: [Robotgroup] Drive a Droid proposal... How to detect the "fence"?

Hey all-

I wanted to see if I could get some ideas on how to accomplish something 
with the "Drive a Droid" proposal we're submitting for First Night.

We are proposing placing the finished R2D2 droid in an "arena" and 
allowing folks to drive the droid and control all its functions (sounds, 
lights, movements) via remote-control.

The issue we're trying to figure out now is how do we make it so the 
droid can "sense" the edges of its "enclosure" and not go "out of 
bounds" when being driven by the "guest driver". The idea would be to 
"disconnect" remote control from the driver long enough to reorient the 
droid to point away from the arena barrier, then give control back.

The "Drive-a-Droid" First Night proposal (draft!) is here:

http://www.notepad.org/Drive-a-Droid6b.pdf

So you get a feel for concept.  :)

I was thinking about placing a CMU cam on the bottom of the droid near 
the "center foot" pointing down and having the droid turn 180 degrees 
whenever it saw its "trigger" color. This might allow us to use white or 
black gaffer tape to mark off the "area" the droid can roam. Just have 
to have a consistent floor color that is high contrast with the tape 
color. I figure we could adapt "line follower" or "Sumo bot" type code 
for this purpose.

It was also suggested that we use an "invisible fence"-type system with 
a low-level RF signal being fed into a ring of wire around the arena.
Have the droid react to the signal.

However, due to the omni-directional nature of the receiving antenna 
(without getting into triangulation) we won't be sure exactly what part 
of the droid is facing the wire so it would be hard to determine what to 
force the droid to do i.e. "turn left" or "back up".

Anyway, I thought I'd throw this out there for some brainstorming. If 
push comes to shove, we could create a "2nd set" of controls and an 
over-ride switch for a trained operator to use to take over for a 
moment, point the droid back to the center and then release control back 
to the guest driver.

So, anyone else have ideas on how to make the droid turn away from the 
roped area?

Vern

-- 
Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course, if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG
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