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.
I think having a separate WTC for the batteries is a good idea. That would be the chamber you would be in and out of all the time and you could leave the electronics WTC alone and not disturb it.
David R. Boulanger
I know the extra WTC will add about $200 to the cost of the ROV, but, as you have said, it will keep the end cap seal wear and tear confined to the battery WTC and not the Navigation Controller WTC which should not have to be accessed except for firmware updates or repairs/upgrades.
Tom C AVD
Since I have been pulling together the major components (WTCs, Thrusters, Control System, Video System, Batteries, Tether) of my ROV, I have started thinking about the ROV configuration.
WTC: two, one for the control system and one for the batteries
Thrusters: start with four and have room for two more
Control System: unfortunately not available anymore, but easily duplicated by hand soldering.
Video System: undecided at the moment
Batteries: 3S 5000mah LiPos
Tether: undecided at the moment, possibly here and run twisted pair though the hose.
A search of the web has revealed a plethora of ROV configurations from simple (inexpensive) to very complex (very expensive).
Blue Robotics Blue ROV looks like a good starting point, but I want to minimize the use of metals like Al or steel that can corrode. Even anodized Al will eventually corrode when used in salt water. The fittings should be of SS.
The design of the configuration should take into account the center of buoyancy and the center of mass.
Comments and thoughts?
Tom C AVD
Here is a PVC configuration that might serve as a baseline:
Design credit jsut210
Tom, Have you looked at Carbon Fiber materials from Goodwinds.com.
David R. Boulanger
I believe Carbon Fiber materials can be tough to cut without the proper tools.
I am trying to build this ROV with materials and tools that the average member has on hand in his garage workshop.
Tom C AVD
Tom, O.K.. Carbon fiber takes a bit of work to obtain. If you cover the material with masking tape it can be cut with nothing more than a jig saw with a very fine blade. Paying very close attention to your ideas and plans.
David R. Boulanger
I have thought of modifying the design by replacing the 90 deg elbows on the end of the upper lateral supports with flat end caps that could be drilled and taped to provide a flat surface for the attachment of a HDPE vertical side panel in place of the vertical PVC pipe risers. I would install the same lateral PVC pipe with flat end caps across the bottom.
The two WTCs could be suspended from the upper support structure. The vertical HDPE flat panels would have cutouts for access to the interior of the chassis and would provide a structure to mount the vertical and horizontal T100 Thrusters.
I could add skid supports to the lower PVC pipe laterals that would protrude below the bottom of the vertical HDPE side panels on either side of the chassis.
Tom C AVD
As usual you are thinking about a lot of options on the design of your ROV. I may consider building one in the near future. I can't really comment on what you just wrote as you are way ahead of me on the thinking and engineering end of the design. I would say this though. After building my own boat with just paper plans of the hull I have learned that I should have designed some things differently. My point is use what ever materials are convenient whether salt water friendly or not. You will probably redesign the ROV after testing and discovering things that you had not thought of for the first design. That would be my approach.
David R. Boulanger
P.S. I am a big fan of PVC. Gotta love all the different types of fittings that are made.
Good words of wisdom, much appreciated.
Yes, I love PVC too as it does come in many shapes and there are specialty version available too.
Tom C AVD
Hi Tom, I too liked the look of the Blue ROV and am considering constructing an ROV of my own, actually live in a pretty good place to use it.
I have a few thoughts.
Where I live, Kelp is a problem and it can easily get caught on complex open frame structure members, so keeping a relatively smooth and simple shape is important for me.
Where you live, you don't have kelp or much weed of any kind (Ok a bit of Sargassum), but coral outcroppings can be a bit tricky too.
I disagree somewhat about aluminum, 6061 works great in salt water, just so you don't have it in direct contact with any other metal like steel or even stainless, which turn it into a battery, in particular the sacrificial anode of a battery.
Basically, PVC, Fiberglass, (especially G10 or FR4) plate and stainless steel are excellent construction materials.
And ABS is available in sheets at TAP and perfectly adequate for a lot of construction and easy to cut with a slow feed and proper tooling.
Fiberglass of any kind is murder on tooling and G10/FR4 or carbon fiber for that matter really require diamond tooling, carbide just can't cut it literally and figuratively.
I have a small 2'x2' 3D gantry router and use structured diamond tooling exclusively on G10 and Carbon Fiber.
That said, it produces relatively toxic dust so you need to deal with that too.
Carbon fiber is a needless expense for ROVs as the weight advantage is kind of pointless and the increase in cost is considerable and G10/FR4 is really, really tough.
(FR4 is flame retardant G10.)
You could go a long way with PVC and Acrylic tubing, ABS sheet and stainless threaded rod without ever having to get fancy and probably come up with a ROV good to 50 to 100 feet or so.
Beyond that I think, it will start to get expensive.
Those blue robotics thrusters are the only way to go and the main question is how many of them do you need.
I think that for simplicity and water proofedness's sake the thrusters need to be stationary although they should all be reversible.
I like your concept of separate battery and electronics bays, easier to ensure the expensive stuff stays out of harms way.
Your design would probably work fine in Florida, but in the Northern California kelp forests, I am afraid it would simply become a permanent fixture on the reef or a good way of harvesting kelp.
I have nearly become one of those myself, when you run out of air below and have to return over the top of the kelp it can get a bit sticky, definitely not a place to panic.
I guess a quadcopter configuration with slight positive buoyancy might work best, then you could use the motors to submerge and for stabilization pitch and then reverse them as needed for horizontal motion.
Probably a six motor system would be best with 4 horizontal thrusters for depth and stabilization and 2 vertical ones for horizontal motion and yaw.
A bit pricey though.
Interested to hear your thoughts on thruster layout and function.
For anyone who is interested in a fairly simple ROV control system that uses Arduino Nanos, try here
It uses a PS2 controller to send topside thruster, camera, and sensor data requests to the ROV Controller in the ROV.
The ROV Controller can be easily interfaced to an APM2.x for stability control in the FBWA Mode.