Let's Make Robots!

ROV submarine

I playing with the idea of building a ROV.

A ROV is a Remotely Operated underwater Vehicle.

I plan to start simple, with a webcam connected to a computer, and 3 motors with propellers controlled by switches, all of it strapped to a frame of sealed plastic tubes. Something close to this instructable

But the robot geek in me wont stop there! I want to build:

A moisture sensor (to warn if the electronics compartment has sprung a leak) 

A gripper (pretty obvious huh? anybody know any simple design that uses a motor, not servo?)

a compass (any good ideas on how?)

PMW controll of the thrusters (done with a microcontroller I guess)

Pan/tilt of the camera.

It seems like controll by umbilical cable is the only option. There is RC submarines on the market, but I cant find out what kind of reception radio signals get under water. Doesn't all the Hollywood movie-subs have to go to surface to get in radio contact? And as a technical breakdown is very likey, a line to pull it back up to the surface isn't that bad an idea anyway.

Does any of you have any suggestions, what kind of technotrickery can I add to impress? maybe a pressure sensor for depth?

Would a picaxe 28X1 onboard and a picaxe 28X1 on shore be able to communicate using one cable for serial communication? -Would that be sufficient to give 3-4 sensor inputs one way and motor/servo controll the other way? 

I think I'd need to be able to controll 4 motors and two servoes (pluss any extra you come up with).

 

I'm sorry for the messy post, writing and thinking at the same time isn't really my expertise. Actually, according to my wife thinking in general isn't... Here's a few other links I've been browsing while writing this post

http://www.homebuiltrovs.com/

http://www.rov.net/ 

 http://www.rcgroups.com/forums/showthread.php?t=1068847 

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Hi Guys,

 Just some comments from an ex RC sub builder

Normal RC (27Mhz - UK land system) works down to around 1.5m as long as the receiver aerial on the sub is totally isolated from the water.  Electronic compasses would be the logical way to go to know the course.  Keeping depth by pumping water in/out is very hard to control enough to hover. Also lets water potentially enter the pressure hull, so flooding can be problem.

Main advantages of umbilical are 1/ no need to carry batteries in hull so sub is smaller. 2/ something to pull on to get sub back in emergency.

 

Hope this helps

 

Pete

 

parallax has got a compass sensor
what about making a compass with a strong rare-earth magnet, maybe a floating one and use a hall effect sensor to monitor it's position? probably not a real accurate method but it would be cheap.
would it be precise? You would need many hall effect sensors to monitor its exact, or even its approssimative, position, and that could make the sensor more costly.

I wasn't sure how well a compass would work underwater, but it seems it might after googling a little. Something about "dive compass". One thing to remember is to read the compass when it is level. To find "level" an accellerometer  or gyro or both in an IMU is needed. Sparkfun has some various electronic compasses, plain as well as those already tilt compensated.

I might try a few underwater tests with a cheaper model before getting an expensive one. Anything, a metal bar nearby, running motors can through off readings.

You could always mount the compass inside a 2-ring gimbal, and use a small weight under the compass to keep it correctly aligned with respect to gravity.

It would change adjustment as the sub accelerates or decelerates.
but then i don't think you can find a solution not affected by acceleration... If it is not important to read its values often then i think this option would work well
Gyros aren't affected by acceleration. But they tend to drift. That's why IMUs make use of both gyros and accels, so that the output of each can be combined through  Kalman filter math to provide a good reference to "up".  Or of mopvement in general.
i meant no better solution as for the self-levelling compass actually, though i'm with you on this one, i too would use sensors to detect proper levelling.