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'm actually getting ready to make a video today of being towed in the Kayak. Also, I have never seen the maximum Amp draw that BR shows on their spec sheet. Its always been a few Amps less. Probably because the thrusters are moving through the water as opposed to being static.
David R. Boulanger
It could also be caused by voltage drop in the batteries or wiring when it's running so that the motors never actually see the full 12V. At less voltage they will draw less current.
When I decided to break vacuum on my Eye of Mine Camera Housing/WTC vacuum test setup I found that I could not get the back of the Camera Housing to open due to the residual internal vacuum in the housing.
It turned out that I had to wait for around 20 hours for the air in the open WTC to leak back up the composite video cable into the Camera Housing before the vacuum was low enough to get the back open.
I believe that this speaks well for the integrity of the Camera Housing seals and the leak proof quality of the composite cable and fittings.
Tom C AVD
It has been almost a month since I last posted and the reason being that I was awaiting the receipt of a tether and interface boards to continue on with the construction of my ROV. Well, I do not have to wait to post anymore as the tether and the interface boards have arrived!
The neutral buoyancy tether cable. and the ROV and Topside interface boards are a beta test versions from Blue Robotics and are not yet available from the Blue Robotics Store. I was fortunate enough to be selected by Rusty to test these beta version components and plan to quickly integrate them into my ROV project and provide Rusty with constructive feedback, if any, as to their functionality. Please remember that I am working with beta components and therefore there may be changes to the final versions depending on the results of the beta testing.
I received 75 meters of the neutral buoyancy tether cable. The construction of the tether is as follows:
The Tether is a high quality tether cable designed specifically for ROVs and other subsea applications. It is neutrally buoyant, has 500+ lb breaking strength, and is embedded with water-blocking fibers to seal any leaks. The tether has a diameter of 7.6mm and is slimmer than the vast majority of comparable ROV tethers.
The tether carries four unshielded twisted pairs (UTP) of 26AWG wire. These pairs are colored and arranged in the same fashion as a Cat5 networking cable including cross-talk resistance. Each pair is individually jacketed inside the cable to maintain reliable properties and minimize interference between each pair of wires.
The core of the cable contains Kevlar strands for strength and Dacron fibers for space filling. Both fibers are impregnated with water-blocking compound to block any leaks caused by nicks or rips in the cable. The high-visibility yellow polyethylene foam jacket resists abrasion and provides neutral buoyancy.
The stiffness of the cable is designed to be flexible enough to give plenty of freedom to your ROV, but stiff enough that it does not become tangled easily.
Here are a couple of pictures of the exterior and interior of the tether cable:
The interface boards provide low-latency video, a serial port connection, and remote power on/off switch for tethers up to 300m length. They can be used with the neutral buoyancy tether or a Cat5+ network cable. The interface boards appear to be of high quality with thick printed circuit base material and extremely legible legends on the board silk screen.
The Tether Interface Board Set is open-source and open-hardware, so the schematics and board files are free to view, modify, and reuse. The electrical schematic and board layout are open-source and the design files will be available to all end users.
I plan to start integrating the tether and the ROV-side Interface Board into my Navigation Controller WTC this weekend and will then give consideration to selecting a topside cabinet for the Topside Interface Board.
Once again, please remember that these are beta test components and could be subject to change in their physical and electrical configurations and specifications before becoming available in the Blue Robotics Store.
More to come.
Tom C AVD
I have attached the ROV end cable penetrator to the neutral buoyancy Tether as shown in the picture below. Since the Tether is 75 meters long I stripped approximately one foot of insulation off of the ROV end of the tether to give me a sufficient length of twisted pairs for connections within the Navigation Controller WTC.
Cable Penetrator on ROV end of Neutral Buoyancy Tether
Since the Tether cable will eventually be wound around a cable drum that will include slip rings, I will hold off making any permanent connections to the Topside end of Tether cable.
The path forward now will be to electrically connect the Topside Interface Board to the ROV-side Interface Board through the Tether cable and then attempt to communicate with the ROV-side BBBMINI Navigation Controller from the Topside laptop running QGC. To that end I have fabricated a bi-directional level shifter to convert the 5 vdc serial output of the ROV-Side Interface Board to the 3.3 vdc input of the BBBMINI telemetry connection. The level shifter is a Sparkfun standard bi-directional level shifter available here. There is no need for a Topside level shifter as the communication between the laptop and the Topside Interface Board is done through a USB interface.
Once the Topside QGC has been setup to work with a gamepad controller Linus and I will attempt to communicate with the ROV-side BBBMINI running an alpha version of ArduSub.
More to come.
Tom C AVD
Looks good, Tom! I'm excited to see this move forward.
Yes, we are now making progress again:-)
Could you provide a picture or diagram on how the ROV end of the Tether cable should be oriented in the Thimbles and where the Thimbles should be attached to the ROV Chassis?
Tom C AVD
Looks good so far! I know it's a bit late in the game with the tether connection already being epoxied in place, but have you considered using wet-connectors for a quick disconnect for the tether?
I have had great success using them on my OpenROV based vehicles, and I find having a detachable tether quite convenient when toting around the vehicle and tether reel. I typically have 100m, but I will be adding another 100m extension. I have been using the SeaCon ones available from Amron.
A bit on the expensive side, but you get what you pay for and having a detachable tether is now a requirement for me.
Thanks for the kudos, much appreciated.
I will take a look at the SeaCon connectors and see what I might be able to do even though the cable penetrator has already been installed.
Tom C AVD
If you do end up using a connector, make sure you place it between the enclosure and the thimble so that the tether still maintains it's pull strength. The Seacon connectors don't have any way to attach the Kevlar strength fibers from the tether.
I would attached the thimble to the tether about 12-18" behind the penetrator, using three thick zip ties to secure the tether to the thimble. Then attach the thimble to your frame near the back somewhere, making sure that the section between the thimble and the watertight enclosure has some slack so that it does not take any force when pulling on the tether.
Also, be sure to attach the thimble so that it can't twist at all. Otherwise, it will twist when you turn the vehicle around a few times and could eventually loosen the penetrator.
Thanks for the input, much appreciated. I will give it a shot.
Tom C AVD