Dock patrolling robot

I was reading the "what do you want your robot to do" thread and I thought this application deserved a new thread. I'd like a robot that will patrol a
dock in order to keep geese and swans off it.
It should: 1. Operate at night and charge during the day. 2. Find its own charging station in the morning and start patrolling on its own at night. 3. Operate between 20 and 90 degrees F. Operation could encompass deciding whether conditions are suitable for patrolling. Maybe the possibility of ice at low temperatures precludes patrolling. However, the dock is used when there is ice or snow on it, so it would be more desirable if patrolling could occur at low temperatures. 4. Distinguish between the dock and the water (which is sometimes frozen). The height of the dock is not always greater than the water. 5. Handle bad weather gracefully - if it is raining or snowing, it should be able to recognize unsuitable conditions and seek shelter at its charging station until the bad weather abates. Or if there's snow or ice on the dock, it could not patrol. 6. Negotiate a fairly steep ramp.
This problem seems pretty straightforward (all the robot has to do is (slowly) wander around a rectangular area and find its charging station) until you start thinking about how to handle the details reliably. What will happen when rain or snow gets on a camera, sonar or IR sensors? How to stay on the dock?
Mitch
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a
<snip>
------
Does that mean that your dock is sometimes under water, or just right at water level? (One assumes that means it's at least an inch or two above water level.)
~WEC
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W.E.Cole wrote:

The part of the dock on which the ramp rests is underwater. The rest of the dock is nominally 4" above water level, but there are waves to consider.
Mitch
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wrote:

quite a list you got there, but maybe you can do something a little different, have the bot trundle out on a cable that's hung from poles over the dock. put in a bb gun, the kind that fire plastic bb's, but use PVA balls, they'll dissolve in water and degrade. a camera in a protected enclosure, maybe a building, would target the 'vermin'(including somebody pilfering petrol), motors and position sensors inside a small building at top of a pole, two sets of pulleys, like this mercilessly hacked up image <
http://img.photobucket.com/albums/v413/sKaar/oddstuff/cable-gun.png.
two stepper motors send the gun unit out, when in position the motors turn opposite directions, then power to a solenoid to pull the trigger. you don't need to tilt the gun, just turn it and change position to aim, the pulleys on the gun itself have the cables attached separately, so the cables on either side can make one half of a power and signal loop. of course you can put a camera on it and send the image back through the power cable, is no biggie, would possibly even help aim.
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Mitch Berkson wrote:

It may be difficult to get the robot to see the dock edge under all these variable conditions. If it's possible; a perimeter wire run around the dock with a signal that's detectable might work under all these conditions. All the same, it's likely to go for a swim from time to time!
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all these variable conditions.
not see, put a spring loades wheel on the side, when it is released a switch will change position and provide feedback to the processer which will tell it that it is near the edge, you could even extend the extra wheel on a rod to be extra safe
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MR Robot wrote:

I am a firm believer in Murphy's laws of robotics. What if the mechanical sensor gets sleet/ice in it and stops responding? Dock-Bot goes for a swim. Should Dock-Bot be a sinker or a floater? If it floats it could be miles away before anybody noticed it's out of bounds. Perhaps a sinker with a distress beacon would aide in recovery. On the other hand if it's a floater you could put a beacon on the dock and have it attempt to regain the dock! Anyway, I can't imagine it staying on the dock.
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put a plastic wrap on it and a heat element, not wuite good for the battery, but you could also make it a boat robot or make it waterproof
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James D Baker wrote:

What about a sinker with a cork on a line?
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    --Although it might be an iteresting mental exercise to use robotics, a big-ass cat or two might do the same thing a little fore reliably... ;-)
--
"Steamboat Ed" Haas : The other night I
Hacking the Trailing Edge! : dreamed about wasabi...
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