Well this video and that one
Well this video and that one should interest you…
• Water sensor? Check this
• Water sensor? Check this out. You could add some sponges and silica gel capsules to help keep moisture away from your electronics. Silica gel sachets are easy enough to get, just go to a shoe store and take them out of all the boxes =D
• Long-wave radio has much better water penetration, which is why modern subs use it, but getting the transmission equipment will be a pain. If you’re not planning on going all that deep, the buoy idea gets my vote.
• Underwater pressure has a very nice linear relation to depth, making calculations very very easy. I recently bought some of these little pressure sensors for a project at work, they were extremely easy to use since they’ve got a little amplifier built in which produces a nice, convenient linear voltage output. You can probably find even cheaper sensors that will still be more than accurate enough for your ROV.
Good luck!
impressive stuff, I
impressive stuff, I particularly liked the san diego ibotics stingray…great design!
I wasn’t sure how well a
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.
I have been thinking about a
I have been thinking about a swimming pool based bot as well. One idea for navigation I had is to place navigation beacons around the pool. So rather than rely on a compass, the bot would locate 2 or more of the nav beacons and determine position relative to those.
Of course this means the bot is dependent on an external system, but since I just have the one swimming pool, that’ll work for me.
You could always mount the
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.
This is a good idea and not
This is a good idea and not hard to make with a couple of rings cut from different size pvc pipe and some bolts.
what about making a compass
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 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.
It would change adjustment
It would change adjustment as the sub accelerates or decelerates.
but then i don’t think you
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
Compass
parallax has got a compass sensor
Gyros aren’t affected by
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
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.
Although the gyro would only
Although the gyro would only be sensitive to rotational movement, the accelerometers would still be affected by the ROV’s acceleration/deceleration. In any case, will the ROV have such significant acceleration to disturb the sensors noticeably, and does it need to read the compass value constantly?
Don’t know, it’s up to
Don’t know, it’s up to maneuver…i personally wouldn’t check the compass quite often but that’s just me.
just to get a general idea
The compass is just to get a general idea of where the ROV is heading. I think a led-style compass with 8 leds would be sufficient I guess. Just to know whether it’s driving towards land or is aiming for the Atlantic Ocean.
Hi Guys, Just some comments
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