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
Replies
Hi All,
Today I potted each of the two horizontal Thrusters' power and control cables, that I had prepared previously for potting, with marine grade epoxy and I also used the excess epoxy to fill the back ends (inside the WTC) of the practice power and control cable penetrators.
Below are pictures of the power and control cables being held in my trusty vice and against my steel peening block while the marine grade epoxy cured:
Front View of Power & Control Cables Curing
While the horizontal Thruster cables were curing I prepared the vertical Thruster power and control cables for potting in their respective cable penetrators. I will pot the vertical Thruster power and control cables tomorrow along with the inside ends of the horizontal Thruster power and control cable penetrators, and finish preparing the other ends of the practice power and control cables for potting on Monday.
More to come.
Regards,
Tom C AVD
Hi All,
At this time I would like to get a dialogue going concerning the tether cable for the ROV.
Since my basic two board ROV control system requires two twisted pairs for bidirectional communication using MAXX 488 differential drivers and one twisted pair for balun driven video, I started considering CAT5/6 cable. Based on my research, tethers can be very cheap to very expensive, but in a way you get what you pay for.
Most of the homebrew tethers are made up of CAT5/6 stranded twisted pair cable or the waterproof version of CAT5/6. Since CAT5/6 tends to have negative buoyancy, many builders will push it up the center of a 3/8" dia hollow nylon rope to help improve its buoyancy and protect it from abrasion since the non-waterproof version has a relatively thin sheath.
Then there is IP68 Ethernet cable. This is excellent waterproof CAT5 cable. One of the draw backs is that the female mating connector end of the cable is too large to fit in the remaining area of the 10 hole End Cap and the price per meter is astronomical in relation to a do it yourself, homebrew budget.
If I go with the OpenROV tether, I will have to convert my two board system to use the Tenda Homeplug adapter in order to use a simple twisted pair tether.
Decisions, decisions. Comments and suggestions greatly appreciated.
Regards,
Tom C AVD
Hi Thomas,
I think this will work well. The RS-485 is really robust and simple. Having full-duplex will allow it to mimic TTL serial and make it plug-and-play compatible with the APM.
Unfortunately the connectors are too big for a 10mm cable penetrator hole! I would love to figure out a better solution for that. Perhaps just 0.1" crimped header pins?
The HomePlug solution is pretty great and gives a lot of bandwidth, but will also require a full computer onboard instead of just an APM. I'm not sure what electronics you have in mind?
Best,
Rusty
@Rusty,
Thanks for the input and observations. Much appreciated.
I thought that I would start out simple with the two board Arduino Nano solution that uses RS485 twisted pair for communication and then move on up to a Beagle Bone Black (BBB) like OpenROV uses.
Linus and I have been working with the MINI cape that is used with the BBB and there is an ArduSubmarine effort in the works, but still has not seen fruition.
I would like to see a Topside controller that is more sophisticated than my two board solution, but not as fancy as a laptop running a Matlab MP type of surface controller.
Regards,
Tom C AVD
Tom,
Are you planning to use video baluns? What kind of display will you attach?
-Rusty
Hi Rusty,
Yes, baluns will be needed to run the video over twisted pairs.
The display I will use will be driven by what control system is in use at the time. If I use the two board Arduino Nano solution I will probably use a small standard video display. If I move to a more sophisticated system such as used by OpenROV and others, then I will probably display the video on a laptop that will also be used for control purposes.
While searching for tether information, I came across an interesting ROV control system called ROV-Suite It makes use of a topside laptop and bottom side Arduino/RPi combination.
Regards,
Tom C AVD
.
@Tom - FYI Chis, the developer for ROV-Suite, is buddies and former school mates with Nick who developed the boards you are using.
@bigkahuna,
Interesting to say the least:-)
Regards,
Tom C AVD
That's a nice looking ROV you're making. I'm a first time builder making my version of a Seafox. I've found a lot of useful ideas on the http://www.homebuiltrovs.com/rovforum/index.php forum. This is the link to mine http://www.homebuiltrovs.com/rovforum/viewtopic.php?f=18&t=1548 and my manipulator http://www.homebuiltrovs.com/rovforum/viewtopic.php?f=18&t=1628.
I'm looking forward to see how yours turns out.
Hi Ian,
Thanks for the links, much appreciated.
I am a member of the homebuiltrovs.com also and I go under the member name of SSN626B/TCIII.
Your SeaFox is quite an impressive build. Using the banana plugs for the motor power connections is very innovative and inexpensive:-) The construction of your manipulator is also very impressive. How deep do you think the manipulator motor seals can go without leaking?
You appear to be using a topside battery to power the Thrusters down your tether? With the capacity and price of LiPo batteries continuing to increase and decrease respectively, I decided to add a second WTC to house the batteries and believe that I can get up to an hour of run time using two 3S 8000mah LiPos in parallel.
I started out with the bilge pump thrusters (I was experimenting with just one bilge pump) also. I then switched to the Blue Robotics T100 Thrusters when they appeared on Kickstarter because I was concerned about the effectiveness of the seals on the bilge pump motors at depth. Mine T100 Thrusters also have the built-in ESC.
I have a VEX mechanical gripper that I have been thinking about using on my ROV, however I will have to replace the VEX servo motor with a waterproof brushless motor, maybe something like the motor in the BR Thruster, but of lower speed like those used in camera gimbals.
I saw a picture of your Taig lathe in your Retro-Retro SeaFox thread. I have one also as well as a Taig Mill. They are really great tools for the price. I purchased a Shearline rotary table for the mill so I could make bigger turret jaws for the lathe.
Regards,
Tom C AVD
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