Experimental ROV Design using Blue Robotics Components

[SSN626B]

Hi All,
I started my experimental ROV by funding for three Blue Robotics T100 Thrusters (https://www.bluerobotics.com/store/thru ... -thruster/) with built-in ESCs when they started their Kickstarter Project early last year.
By the time that the T100 Thrusters had arrived earlier this year I had already decided to add a fourth Thruster and Blue Robotics had begun to offer a selection of WTCs on their website (https://www.bluerobotics.com/store/). So I ordered a fourth Thruster and two 4" diameter WTCs (https://www.bluerobotics.com/store/wate ... e4-asm-r1/) configured with clear End Caps on the front and 10 hole End Caps on the rear and the necessary cable penetrators (https://www.bluerobotics.com/store/part ... r-10-25-a/).
I chose to use two WTCs so that besides the navigation controller WTC I would have a second WTC to hold the LiPo batteries as I had decide not to try and power the ROV from the surface which just adds weight to the ROV tether. Therefore the tether would just carry communication and video lines and be very light weight.
Below are some pictures of the ROV hardware:









The T100 Thruster ESC can be controlled by either PWM or I2C signals.
I chose one blank acrylic End Cap (front of WTC) and one with 10 holes for power, Vent Cap, and instrumentation wiring penetrations (rear of WTC).
Two of the O-rings are used to seal the O-ring Flanges in the WTC tube while the third O-ring is used to seal the acrylic End Caps to the face of the O-ring Flanges.
The blank Cable Penetrators can be used to either make custom penetrators for cables other than 6mm dia or to block off unused holes in the acrylic End Plates.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,
Now it was time to decide what the ROV chassis was going to look like.
I was thinking of a ROV configuration that minimizes the use of metal which can corrode in salt water.
Here is a ROV chassis made strictly of PVC pipe:

Design credit jsut210

Here is a ROV chassis constructed mainly of HDPE panels:

Picture courtesy of MSOE

I finally decided I would like to try a hybrid configuration where the vertical PVC pipe risers are replaced by HDPE panels and the cross bracing is constructed out of PVC pipe.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,
So I purchased two .5" x 12" X 24" sheets of HDPE for the ROV chassis construction. I had originally planned to use .25" thick HDPE, but the reviews indicated that it warps easily compared to the thicker sheets so I purchased the .5" thick sheets. HDPE has a specific gravity of 0.95 gm/cm^3 which is very close to neutral buoyancy.

I had decided to mount the vertical Thrusters in the middle of the long axis of the chassis and mount the horizontal Thrusters straight ahead at the stern of the chassis.

If the chassis is statically balanced about its pitch axis, then mounting the vertical Thrusters at the center of the long axis of the chassis should minimize any pitching of the chassis as the ROV rises and descends vertically.

Mounting the horizontal Thrusters at the stern will allow rotating the ROV chassis about its center of yaw and still providing adequate forward and reverse horizontal thrust if I eventually go to a six Thruster configuration and turn the horizontal Thrusters at a 45 degree angle.

I believe, correct me if I am wrong, you want the center of gravity of the ROV low on the chassis and the center of buoyancy high on the chassis.

Since the WTC containing the LiPo batteries is going to be the heaviest component on the chassis, it should be mounted as low as possible on the ROV chassis followed by the navigation controller WTC spaced vertically some distance above it.

Since I went with HDPE panels that are 12" x 24", but really measure out at 11.75" x 23.75", I was limited to a solid side height of 11.75". If I add up the heights of the WTCs and the thickness of the horizontal Thruster I come out with a vertical height of 13.45" without even considering the thickness of any mounting structure between the two WTCs. So I had already exceeded the height of my HDPE panel.

At this point I began thinking about mounting a PVC pipe skid structure, of yet to be determined height, below the bottom of the HDPE panel to provide support for the battery WTC and then stack the navigation controller WTC above it. This will provide the additional vertical height needed for the thickness of the vertical Thrusters at the top of the chassis without them protruding over the top of the HDPE plate.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,
Since the HDPE plates on Amazon are 1/2" x 11 3/4" x 23 3/4", I decided to make the chassis 22" long x 15" wide x 11 3/4" tall. To visualize the chassis, picture a Star Wars Tie Fighter head on. The Tie Fighter's vertical solar panels are the chassis side plates and the center control module between the solar panels are where the WTCs will be attached in an over-under configuration to a 14" wide by 8" deep cross brace.

I have completed the center plate that is 14" wide x 8" long that will be used as a cross brace between the two chassis side plates and will provide a mounting point for the two 4" dia WTC that will be mounted in an over-under configuration.

The two horizontal Thrusters will be mounted on HDPE 3 3/4" x 3 5/8" platforms, that are cantilevered from the side plates, at at the rear of the chassis

The vertical Thrusters will be mounted at the midpoint of the 22" chassis with the top of the Thruster just below the top of the chassis.

Since HDPE has a very slick surface, I covered the first side plate with blue painters tape and laid out the necessary cutouts in the chassis for weight reduction and then went ahead and used a saber saw to make the cutouts.

The first side panel is just about done and I will shoot some pictures of the it and the cross brace tomorrow.

I will then proceed to start on the second side panel and the top and bottom lateral cross braces that will 14" long by 1 3/4" in width.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

Here are a couple of shots of the ROV chassis beginning to take shape:



Above is a shot of the left side of the chassis. The six Philips head ss 10-24 screws in a row are used to attach the cross brace/WTC support to the left side of the chassis. The three holes to the lower middle right side of the chassis are for three Philips head ss 10-24 screws that are used to attach the horizontal Thruster plates to the side of the chassis plate. The cutouts help to reduce the weight of the chassis plate.



Above is a shot of the backside of the left chassis plate and the cross brace/WTC mount. The slots in the cross brace are 4" x 4" and are designed to allow the free flow of water from the vertical Thruster which will be mounted between the cross brace and the top of the side plate on the inside of the plate. Also visible in this shot is the blue tape that I attached to the inside surface of the left chassis plate in order to be able to draw on the HDPE surface which is very slick to say the least.

Tomorrow I hope to start and possibly complete the right side chassis plate and prepare it for attachment to the cross brace. After which I will begin to attach additional 1 3/4" cross braces along the bottom and the top of the chassis side plates. I suspect that I might have to add additional buoyancy material to the chassis to achieve neutral buoyancy and that material can be attached to the upper cross braces. Additionally the lower cross braces can be used as hard points to mount a pair of skids to the bottom of the chassis.

More to come.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

I got a lot accomplished today!

I completed the installation of the chassis right side cantilevered horizontal Thruster support and then moved on to complete the attachment of the chassis right side panel to the cross brace/WTC support.

After attaching the chassis right side panel to the cross brace/WTC support, I mocked up the ROV chassis with a horizontal and vertical Thruster and positioned one of the 4" dia WTCs on the center of the cross brace. Pictures of the mockup are below:


Chassis Right Side


Mocked up Chassis Front View


Mocked up Chassis Rear View


Mocked up Chassis Top View

As can be seen in the top photo, the WTC will not be centered horizontally on the cross brace. The reason for this positioning is to help offset the horizontal Thruster weight aft of the horizontal center of mass and to provide clearance for the cables between the rear of the WTC and the rear horizontal Thrusters. There will be an identical WTC mounted under the upper WTC to hold the LiPo batteries.

Tomorrow I will start on constructing and installing the upper and lower cross braces. They will provide additional lateral stiffness and serve as hard points for mounting skids on the chassis bottom and for mounting additional buoyancy tubes on the top of the chassis if necessary. The cross braces will be made up of leftover HDPE from the chassis construction and will consist of two 1/2" x 1 3/4" x 7" HDPE plates butted together and connected with a 1/2" x 1 3/4" x 3" bridge plate. I plan to test the JB Weld epoxy on the cross braces to see how well it adheres to the HDPE.

More to come.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

Today I completed the fabrication and installation of the additional cross braces on the ROV chassis. The additional cross braces are mounted front and rear at the top of the chassis and front and rear at the bottom of the chassis. The cross braces were fabricated from leftover HDPE during the construction of the ROV chassis side plates. The additional cross braces will provide hard points to mount skids at the bottom of the chassis and additional flotation material at the top of the chassis if necessary. The two pictures below show where the additional cross braces are located:

Cross Braces Front View


Cross Braces Rear View

Tomorrow I plan to begin the fabrication of the WTC mounting structure. I plan to cut strips of HDPE and then bevel one edge that can be wedged against each side of the WTC outer circumference to locate the WTC laterally on the main cross brace/WTC support. I will then see about the availability of stainless steel straps to provide a vertical clamping force of the WTC against the main cross brace/WTC support surface.

More to come.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

Today I completed the fabrication of the pieces of HDPE that will make up the WTC mounting cradle.

The mounting cradel is essentially a tower composed of three 1/2" x 1 7/8" x 1 1/8" blocks with the top block having a 30 degree angle cut on its inside face which will be tangent to the side of the WTC at its outer circumference. There will be four towers with two at the front and two at the back of the WTC and will center the WTC latterly on the main cross brace/WTC support.

I plan to use the JB Weld epoxy to glue the blocks together, sand to shape, and then drill vertical holes in the blocks to accommodate 6-32 screws that will hold the tower in place on the main cross brace/WTC support.

I hope to have pictures of the mounting structure by shortly.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

On Monday I glued the HDPE pieces of the WTC mounting cradle blocks together with the JB Weld Polyethylene/Polypropylene adhesive which worked great and finished cutting and sanding them to size on Tuesday morning. I then epoxied 1/8" thick rubber strips to the faces of the cradle blocks where they will contact the sides of the WTCs.

At this point I was ready to spot and mount the cradle blocks on the main cross brace/WTC support. I had decide to use ss 6-32 machine screws to attach the cradle blocks to the main cross brace/WTC support. To begin the spotting and mounting process I drilled two #36 tap size holes in each cradle block. The idea here is to be able to clamp the cradle blocks into position against the WTC tube and then use a #36 drill to spot a hole in the cross brace for each of the cradle block mounting hole pairs. The front of the forward cradle blocks was positioned flush with the front face of the main cross brace and tangent to the circumference of the WTC tube while the rear of the aft cradle blocks was positioned flush with the rear face of the main cross brace and tangent to the circumference of the WTC tube.

In the pictures below the cradle blocks can be seen clamped to the main cross brace up against the WTC tube. In the first picture I have aligned the cradle blocks to the WTC tube and the main cross brace and have drilled the first #36 hole in the main cross brace for each of the cradle blocks. I will then tap the #36 holes in the main cross brace with a 6-32 tap for the ss 6-32 machine screws. Since the clamps block one of each of the hole pairs in the cradle blocks, I must repeat the spotting process for the second hole after I have drilled and taped the first 6-32 hole for each cradle block in the main cross brace.

After I have spotted, drilled and taped the eight 6-32 cradle block mounting holes in the main cross brace I will counter bore the #36 hole pairs in each cradle block with a #28 clearance hole drill for the insertion of the 6-32 ss mounting screws.


Front View of Chassis with Centered WTC and clamped on Cradle Blocks


Chassis Left side showing the WTC and clamped Cradle Blocks

Tomorrow I will drill and tap the first cradle block attachment holes in the the main cross brace/WTC support and attach each of the cradle blocks to the main cross brace so that I can complete the spotting of the second cradle block mounting hole in the main cross brace. I will then drill and tap the second set of cradle block attachment holes in the main cross brace. At this point the upper WTC tube cradle mount should be done except for the addition of slots to be spotted in the main cross brace to allow the passage of marine grade Velcro straps through the main cross brace in order to hold down the WTC tube to the main cross brace while it is seated in the cradle mount.

More to come.

Regards,
SSN626B/TCIII

[SSN626B]

Hi All,

Today I completed the installation of the upper WTC support cradles on the main cross brace/WTC support. Tomorrow I will begin the installation of the lower WTC support cradles on the main cross brace/WTC support.

The pictures below show the location of the upper WTC support cradles on the main cross brace/WTC support:


Front View of Main Cross Brace with WTC Support Cradles Attached


Top View of Main Cross Brace with WTC Support Cradles Attached


Top View of Main Cross Brace with the Upper WTC positioned on the Support Cradles

Presently I am thinking of holding the WTC down on the support cradles with marine grade Velcro straps. The straps would wrap around both top and bottom WTCs through slots cut in the main cross brace/WTC next to the sides of each WTC.

Once the WTC support cradles and hold down straps are installed I will move on to mounting the four Thrusters in their respective horizontal and vertical positions. Then comes the more difficult part of this ROV project, the potting of the Thruster power and control wires in the WTC end cap cable penetrators. Fortunately for me Blue Robotics has several very good tutorials on preparing the cables for insertion in the cable penetrators and then their epoxy potting in the cable penetrator feed through shafts.

More to come.

Regards,
SSN626B/TCIII