HVAC Duct robot

Does anyone have experience with RF (video) transmission from an untethered mobile robot deep inside a heating duct? Is there some frequency where the
duct would serve as a reasonable waveguide? Perhaps the bot could negotiate with the receiver to select the best "channel" or frequency based on the section it is in - this negotiation could perhaps take place using audio or ultrasound - which may be good enough for arbitration but not high enough data rate to serve video. Any ideas? Winter's here and I'm curious what's lurking in our ducts.
Kevin
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Sounds like a fun project. Question, does it HAVE to be untethered? Having a tether might really help, both for power/signal reasons and in terms of having a way to yank it out of being stuck somewhere.
I'm thinking of building something to navigate the crawl spaces in my house, so I'm interested in hearing more about what you do. Hope you post progress here.
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I thought it would be more fun and challenging to go untethered.

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Fair enough. If you already have 802.11 hardware, could you do a simulation down at the local duct shop? Might be a cheap way to find out if you can use stuff you have on-hand.
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: Does anyone have experience with RF (video) transmission from an untethered : mobile robot deep inside a heating duct? Is there some frequency where the : duct would serve as a reasonable waveguide?
I think there was an article on this topic in the past year, either in Circuit Cellar or Servo. A quick google didn't find anything, maybe someone else remember exactly where/when?
The specific one I'm thinking of used IR at first, and that one got stuck, so then he moved to method 2 -- that I don't remember.
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I used a Roomba on my parents duct work. Let it go, and wait for it to come back!
Does that count?

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You're joking right? In case you're serious - how did you coax the Roomba into doing all four walls of the duct?
I used a Roomba on my parents duct work. Let it go, and wait for it to come back! Does that count?
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Didn't really worry about the walls, was mostly after all the accumlated dust bunnies. It actually did a fairly good job, all things considered. But had to empty it everytime it came to the duct that I was guarding. Recommend vacuuming everything you can reach, or use extended small brushes to push the big peices out.
I don't think the owners manual said I *couldn't* use it on the duct.
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Kevin Gomez wrote:

I think the general idea is that the majority of the dust will accumulate on the floor of the duct. The real concern is ensuring the Roomba has adequate battery life so it won't die out-of-reach in the middle of a duct.
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Thanks for all the helpful responses. I'm all for the "just do it" mentality - but to belabor the issue a little longer;
I came across this link which is a waveguide primer. http://www.microwaves101.com/encyclopedia/waveguide.cfm
Many of my ducts are ~22inches x 8 inches. Considering just a straight section for now, does this mean that I would get significantly better range for a given transmitter power if I use 300-500MHz rather than 2.4GHz. How much does it matter if conduction is poor across seams between sections. Does it matter if the 'waveguide' is magnetic (sorry it's been a while since I did EM classes).
Kevin

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