Hi All,

I am sure that many of you have heard of the OpenROV Project which involves building your own ROV from a kit. I am an experienced model builder with plenty of experience and a reasonably equipped workshop, but I was a little taken aback at the complexity of assembling the OpenROV from their kit of parts. It seemed to me to be a high school to college level project requiring a small team of experienced modelers to successfully put the OpenROV together though I could be wrong.

It appeared to me that there were a number of critical assembly requirements that had to be performed spot on as there was no going back to realign or reseal once the assembly was completed. Therefore I have been looking around to see if there might be an easier way to design and build a ROV similar to the OpenROV without having to perform some of the critical assemblies required to complete the OpenROV.

One area of the OpenROV design that I took exception to was the thrusters. They were not going to last very long when immersed in seawater due to the exposed bearings and stator/armature. To me this was a kind of deal breaker as to the questionable lifespan of these thrusters. I know that commercial thrusters are not cheap (think Seabotics or CrustCrawler) and the OpenROV project was just trying to overcome the high price of commercial thrusters with their homebrew design. Still the unknown lifespan of the OpenROV design did not leave me with a warm feeling to say the least.

Then came along Blue Robotics and their T100 Thruster KickStarter Project Link. Their design approach looks good and they have actually tested and characterized prototypes of the thrusters they will deliver to the pledgers. With the addition of the in-thruster water cooled ESC this design becomes very attractive in that it reduces the number of wire penetrations in the Water Tight Compartment (WTC).

Great! Now we have a source of reasonably priced thrusters so what is next? Well, that is where you, the ArduBoat members, come in.

Let's start thinking about the WTC, navigation controller, communication, power, ballast, buoyancy, etc. and attempt to come up with a reasonably priced ROV that the average ArduBoat member might want to consider building.

Regards,

TCIII AVD

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Replies to This Discussion

Tom, 

Even sealing it up in an air conditioned car might help with the high humidity environment we live in.  Never tried the moisture strips or packets though.

Regards,

David R. Boulanger 

#9 lead shot would get my vote.  Very little air space or epoxy space between the shot.  You have to buy a 25# bag unless you have a friend with some.  It's a winner as far as density goes but pricey.  We use it in model sailboat keels.  About $2 a pound I think at Bass Pro Shops

Regards

David R. Boulanger

Hi David,

Thanks for the suggestion, much appreciated, but for the amount of ballast I think that I will need, the bbs are still the most cost effective.

Regards,

Tom C AVD

I just happen to have several tins of lead air gun pellets that I will likely use on my build.  If I didn't already have them I probably wouldn't consider using them as I'm sure there are cheaper sources for lead out there.

Don't forget to leave some ballast for trimming the ROV fore/aft and port/starboard as well as adjusting for fresh/salt water and tooling changes.

Hi All,

Today I removed the 4 mm bullet connectors that came with the HK Turnigy 5000mah 3S LiPo batteries and replaced them with E-Flite EC5 battery connectors that can handle up to 120 amps and are much easier to connect and disconnect. I also reworked the battery hold down strap slot in the battery sub tray so that there is now both one on the top and one on the bottom of the tray. I purchased a set of these Velcro black cable straps to hold the horizontally stacked batteries in position on the battery sub tray. A picture of the battery sub tray with batteries is shown below:

As far as the ballast effort goes, I purchased a 2 foot long piece of 1 1/4" ID diameter PVC at Home Depot and four rounded end caps. After doing a little math I decided to slice a 17 inch section off the original 2 foot piece. I then attached a rounded end cap to one end of the tube and began to fill the tube with my bb supply. I was able to use almost all of the bbs (~5 pounds) to fill the 17 inch long tube before I had to put the other end cap on the tube. If I drill a hole in one of the end caps, I can fill the tube almost all the way to the top with bbs and then use the Loctite marine grade epoxy to seal the hole off. But in the meantime I will keep the end cap just pressed on until I see if this 5 pound ballast tube will get the ROV Chassis close to neutral density. Though I think that it is going to take two 5 pound tubes of ballast to get the ROV Chassis close to neutral density.

More to come.

Regards,

Tom C AVD

Hi All,

The weather here in southern Florida has turned cool, cloudy, and slightly rainy so I have been unable to test my ROV chassis in the Association swimming pool with the newly constructed 5 pound ballast.

However while I have been waiting for the weather to clear up I have had a chance to test a new Blue Robotics product designed to simplify the vacuum testing of WTCs. Unlike the original vacuum tube adapters which consisted of a 1/4 X 1/4 tubing coupler epoxied into a 6 mm cable penetrator, this vacuum tube adapter takes the place of the screw-in plug used in the enclosure vent so there is no additional cable penetrator to install for testing as before. The pictures below show the vacuum tube adapter and its installation in the enclosure vent:

Vacuum Plug with O rings and Test Plug

Vacuum Tube Adapter installed in Enclosure Vent

Once I got my vacuum pump, gauge, and cutoff valve attached to the new vacuum tube adapter I pumped the Battery Compartment WTC down to 560 mm Hg, shut the vacuum cutoff valve, and waited for an hour. Just like when using the original vacuum tube adapter, the vacuum gauge reading remained at 560 mm Hg and I am sure that it will show a loss of around 20 mm Hg after 24 hours just like the original setup due to the vacuum cutoff valve leaking.

I must commend Rusty on his ingenuity concerning the design of this vacuum tube adapter which has now made the vacuum testing of the BR WTC a slam dunk.

Regards,

Tom C AVD 

 

Thanks, Tom! I'm glad it's working well for you.

-Rusty

Hi All,

Today I was able to check the buoyancy of the ROV Chassis with the batteries installed in the Battery Compartment WTC and with the 5 pound ballast PVC tube.

With the batteries installed in their normal position in the Battery Compartment WTC the chassis still had some positive buoyancy, but the chassis was now trimmed fore and after whereas before it was tilting towards the stern due to the weight of the cables/cable penetrators in the WTC rear End Caps.

Addition of the 5 pound PVC tube at the center of the longitudinal axis of the chassis caused the chassis to maintain its trim, but be just slightly submerged indicting that I was now getting close to neutral or slightly positive buoyancy.

I will now empty the bbs from the 5 pound ballast PVC tube, cut it in half, fill each half with the bbs, and seal the ends of both tubes. The two tubes will be mounted on the bottom of the chassis at the center of its longitudinal axis. This should result in a ROV chassis that is trim fore and aft and is very close, if not at neutral buoyancy.

Now someone might point out that I have not included the Navigation Controller hardware which could add some slightly negative buoyancy, however I do not doubt that the addition of a slight amount of negative or positive buoyancy can be easily compensated for.

More to come.

Regards,

Tom C AVD 

Tom,

Great! What buoyancy are you shooting for? Most ROVs are slightly positive, which helps out with safety if you lose power and also means the vertical thrusters will be trimmed pushing down, which won't disturb the sediment on the bottom.

-Rusty

Hi Rusty,

Thanks for the insights, much appreciated.

After some web research I am going for slightly positive buoyancy as you have suggested.

Regards,

Tom C AVD

Hi All,

I completed splitting the 5 pound 17 inch ballast tube in half and fabricated two 8 1/2 inch tubes that weigh approximately 43 ounces (2.7 pounds) each for a total of approximately 5.4 pounds of ballast.

Each ballast tube is mounted on the bottom of the ROV Chassis at the mid point of the longitudinal axis of the Chassis. The picture below will give you an idea of the ballast tube construction and their mounting location on the Chassis:

Ballast Tubes mounted on the bottom of the ROV Chassis

The ballast tubes are a slip fit in their U shaped clamps and can be moved fore and aft to help trim the Chassis. I plan to use tie raps around the tubes on either side of the cross brace, on which the tubes are mounted, to keep the tubes from sliding in the U shaped mount.

This weekend I plan to finish the Battery Tray and connect the Power Junction Board cables to their respective cable penetrator cable connections and complete sizing the length of and installing the connector on the Power Junction Board battery input cable.

More to come.

Regards,

Tom C AVD  

Hi All,

Today, with the help of my son-in-law, I was able to check the ROV Chassis buoyancy and trim by immersing it in the Association swimming pool.

The addition of the two 2.7 pound ballast tubes to the bottom of the Chassis brought the buoyancy of the Chassis to a point such that the top of the Chassis was just awash in the pool water. This level of buoyancy puts the two vertical Thrusters just about three inches below the surface of the water. Also the present buoyancy is such that when the Chassis is manually forced downward into the water, it will slowly rise back to a point where the top of the Chassis is just slightly above the pool surface.

The following two pictures will give an idea of the ROVs present buoyancy:

ROV Chassis with the two 2.7 pound Ballast Tubes attached to the bottom of the Chassis

The ROV Chassis is just slightly awash in this shot

Once the Chassis has dried off I will begin installing the Battery Compartment Battery Tray and then move on to the Navigation Controller Compartment Controller Tray.

More to come.

Regards,

Tom C AVD  

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