22

You may want to consider a Magnetically Coupled Drive. Use a standard motor with a magnetic coupling to transmit the torque to your prop. This would allow your motor to be completely sealed inside your vehicle: From Eric Stackpole's article mentioned above. Image used without permission, but with attribution. This solution may or may not be suitable ...


22

I'm not sure if an 'aquabot' is a fully submersible vehicle, or a surface one. If it's a surface vehicle, then you just need to look at RC boats. They've got this solved pretty well. The seal that prevents water entering the boat is called a stuffing box (4 on the diagram). It's simply a tube stuffed with grease. The grease prevents any water leaking into ...


14

The best commonly available battery technology when it comes to power density versus weight, and at reasonable cost, is LiPo. I would prbably recommend LiFePO4 batteries. LiFePO4 are somewhat more expensive than LiPo for the same watt-hours, and weigh somewhat more, but they hold the charge better, they age much better, and they can be re-charged five to ...


12

If you're looking for a very cheap way to do it (as in, educational budget cheap), check out the Sea Perch ROV build manual. Full disclosure, I used to work at the MIT lab that heads up this educational program. On page 9 of that PDF it starts talking about how to waterproof a hobby motor with a film canister and toilet bowl wax. The entire housing ...


8

There is no right answer. However, I think I can clarify what you've read so far. You need a buoyancy engine to supply the thrust, wings to direct that thrust, and some ability to change your pitch angle when you change the buoyancy. So, you'll need to balance the strength of your engine with the drag created by your wings. At the same time, your wings ...


7

Keep in mind that "heavier" is not quite the term you're looking for. You should be trimming your SeaPerch to be neutrally buoyant, so unless the new payload creates significantly more drag than your old one, your existing motors should work fine (just with decreased acceleration in response to the increased mass). The answer to the question of torque vs ...


6

When taking into account size / weight / Ah, fuel cells and micro power turbines have an energy per kilogram and (with liquid fuels) an energy per liter that is an order of magnitude better than any battery. In particular, I keep hearing that liquid methanol fuel cells are "relatively practical". a b c d e. And I've heard that Hyuk Kim and Seungdoo Park ...


6

Localization under water was always a problem in ocean robotics as electromagnetic signals do not propagate very well in water. I think your best localization sensor in that case would be the good old sonar, which works much faster in water. You could have four of them and detect how far are the pool walls on each side then with a triangulation algorithm ...


5

Lithium Ion Polymer batteries are probably your best bet. They will present the least amount of magnetic interference (followed by Alkaline... NiCD interferes the most). Unlike the regular lithium ion cells (which are usually round), these ones will stack nicely. I hope you'll check the manual before trying this -- many of them are pressure tolerant. ...


4

If it's actually underwater, how about a webcam looking at the tile pattern on the floor? (Could be considered "cheating" as it will obviously fail in a natural lake, for example.) You can find a paper using and demonstrating this method is this paper: Carreras, Marc, et al. "Vision-based localization of an underwater robot in a structured environment." ...


4

The simplest sensor you can build is a weight on a string. Lower it down until the tension of the string is reduced. I assume you want sonar. So just go buy one they are dead easy to interface to. You can buy these at marine hardware stores. They are not cheap. Look for a depth finder that has "NMEA" output. You may have heard of NMEA as the data format ...


4

One of the prime sensors for global localisation on land is GPS. This is not an option underwater because electromagnetic waves get absorbed quickly. There are however alternatives, which provide navigation information which is not so easily available on land. Large Baseline (LBL) - is a method based on sonar, which works very similar to GPS, just using ...


3

If you cannot use a camera the task is nearly impossible with your money limitations. Professionals use a scanning sonar like the tritech micron and a particle based localization like [3] based on FastSLAM: [1]. However if you experienced with underwater acoustics you can try to build your own localization system based on the idea of a USBL idea [2] e but ...


2

I have come across all the suggestions in the other posts. I don't understand why people are suggesting complex and expensive solutions which are also not feasible. A mechanical seal is the simplest answer for sealing the motor or making it of IP 68. We can use this motor to a depth of 20 m in sea water. The construction is like a WET pit. Such types of ...


2

For maritime robotics, you should definitely take a look at MOOS. It is a similar middle-ware to ROS, but was originally developed at the Dept. of Ocean Engineering at MIT with Prof John Leonard. So it has a heavy maritime bent to it, but can of course be used for terrestrial (or aerial) robotics as well.


2

Take a look to rock-robotics.org and github.com/auv-avalon we provide a lot of basic tools already but in the end there is no real best middelware.


2

Variable ballast on ROVs in practice is usually limited to just the really big ones, for several reasons: In general, you only need to vary your ballast when you're trying to get an exact amount of buoyancy at great depth -- when that amount would be different than at the surface (due to compression of various components) The pressure housing required adds ...


2

Another sensor that you should investigate is ultra-short baseline (USBL). I have used the MicronNav with success in the past. You mentioned accelerometers, but what I think you really meant is an inertial navigation system. These fuse data from accelerometers, gyros, compass, and optionally GPS for a more accurate dead-reckoning. I have used the ...


2

Is the robot going to have an over-the-water antenna? If not, then electro-magnetic communication is a no-chance under-water, if the water is salty (seas, oceans) or if the distances are long. The underwater communication is usually done with sound (acoustic waves) - which can travel huge distances, thanks to the higher density of water, compared to air. ...


2

The simplest answer would be to use the phase difference to calculate the direction -- rotate your array until all sensors get the same phase, and you've found the direction to the source (or do some calculations based on the phase difference -- this does not require any mechanical movement). For the distance -- use two separate arrays and triangulate the ...


2

You don't gave all information that are needed for such calculations. However, the technical details of the Thrusters give a peak consumption of 350 Watts each. So you have 6 of them, makes overall 2.1kW/h. Lets assume your Batteries have the following details: 6S 22.2V 3300mAh. Therefore the amount of energy the Batterie stores is: 22.2V*3.3Ah = 73.26W/h. ...


1

It sounds to me like you've got cavitation. Basically, the blades are turning so fast that the water around the blades boils. Boiling can happen at normal pressure and high temperature, like on a stove, or at normal temperature and low pressure, as in your case. The blades boil the water, then the prop is surrounded by vapor instead of water and there isn't ...


1

If you can't localize, you can't do anything that requires localizing. If you can't use wheel encoders accurately enough to do a rectangular fill (parallel lines) then, by the same reasoning, you can't use them to do any other shaped fill pattern either (concentric circles, spirals, etc.). I only see one real solution here (that's not random walk), but its ...


1

I haven't used ROS before, but you could try to determine the pressure units with an experiment! Put your sensor in water and take a pressure measurement. Lower the sensor 10.3 meters, or about 34 feet, and take another pressure measurement. Subtract (1) from (2), and look for the correct "ballpark": ~1 = bar ~14.7 = psi ~101 = kPa ~1,000 = mbar ~101,000 ...


1

So this is really a hard task. Estimating the position of a AUV is still a large challenge even in research. There are sensors like as DVL (Doppler Velocity Log) available that can estimate the speed over ground. These sensors working okay, but they only estimating the speed. These devices are precise enough for your use case BUT these devices are to large ...


1

I understand exactly what you are talking about. I am developing my own ROV that will have a track system and crawl on the sea floor. If I may suggest placing your motor in a high point in your ROV with the gear drive close to the bottom, you can install a pressurized air system that will allow air into the chamber as the ROV goes deeper. Think of it like a ...


1

On one of my remotely controlled boats, I used this design... The blue discs are flywheels. They are attached to the green rods which are hooked to both sides of a flexible, waterproof membrane. The membrane is fixed to both sides of the casing so it will transmit the motion, but it will not let water through.


1

Take it for what it's worth, I was next to the OpenROV booth at Maker Faire and their answer was 'let it leak and dry it off later'. They said they were surprised that water getting into the motor didn't cause issues for them. 'course I haven't tried this myself and I may have misheard them -- or perhaps nothing had failed for them yet :-) It may be ...


1

All seals leak. If you are able to enclose the motor so that the shaft is the only exit point, fill the motor with a low viscosity non conductive oil such as mineral oil. This greatly reduces the pressure difference across the seal.


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