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,
While I was cleaning the grooves on one of the Navigation Controller WTC End Cap O ring Flanges I discovered a very small nick (scratch) in the bottom of the second from the front O ring groove.
The nick (scratch) is probably 0.005 - 0.010 inch deep and about 0.125 inch long and is perpendicular to the circumference of the O ring groove. I discovered it because it was deep enough to cause the Q tip that I was using to clean the O ring groove to catch on it and stop.
Since it is in the second from the front O ring groove, it may not be a problem as the first O ring seal may be able to maintain the water tight seal. However if I cannot maintain the same vacuum loss over time (1 mm/hour) that I did with the Battery Compartment WTC, it might be wise to replace the O ring Flange as a safety precaution assuming the cable penetrators are not leaking also.
After completing the assembly of the Navigation Compartment WTC I opened the cutoff ball valve and commenced to pump down the WTC to 560 mm Hg. After waiting an hour I started the vacuum pump, pumped down the vacuum gauge tubing circuit to 560 mm Hg and then opened the cutoff ball valve to the WTC. Much to my relief the gauge did not move indicating that the Navigation Controller WTC was holding the same vacuum level over the same period of time as the Battery Compartment WTC. So it presently looks like the nick in the bottom of the second O ring groove has not had an impact on the WTC's vacuum seal (water tight) capabilities.
I then made sure the Navigation Controller WTC vacuum was still at 560 mm Hg, closed the cutoff ball valve for a second time and waited two hours before measuring the vacuum level in the WTC. Again, much to my relief the WTC's vacuum level was still at 560 mm Hg. After closing the cutoff ball valve for the third time, I plan to wait approximately 20 hours before measuring the WTC's vacuum level again. If I measure a value of around 540 mm Hg, as I did with the Battery Compartment WTC after waiting 20 hours, then I am pretty confident that it is my clunky test setup that is leaking, probably at the cutoff ball valve, and not a leak in the WTC.
Navigation Controller Vacuum Leak Test Setup
Once I have completed the WTC vacuum checks, I will attach the ESC Power cables to the Power Junction Board battery cables and prepare to install the two 3S 5000 mah LiPo batteries and associated power cable connectors. This will be followed by installing the ESC Signal Junction Board on the Navigation Controller platform, attaching the ESC Signal cables to the Signal Junction Board, and then installing the ROV bottom side controller board and associated signal and power cables.
More to come.
Regards,
Tom C AVD
Hi Tom and all,
We're aware of the small nicks on the O-ring flanges. They are actually caused by the fixtures used to hold the parts during anodizing. We were pretty worried about them, but after extensive testing we haven't had a problem with a single one. Regardless, future batches of parts will use a redesigned fixture so that they will not have any issues.
Tom, glad to hear that you had the same successful test results. Everything is looking fantastic and it's fun to follow along! Looking forward to seeing it in the water!
Best,
Rusty
Hi Rusty,
Thanks for chiming in on the nick issue. Much appreciated.
Hopefully my ROV Project Discussion Thread will encourage other Group members and maybe some of the members over at homebuiltrovs.com to use your excellent ROV components in their own ROV designs.
After completing the Battery Compartment and Navigation Compartment WTCs about all that is left is fabricating or purchasing the Tether cable.
Regards,
Tom C AVD
Hi All,
More good vacuum testing news!
After replacing the Battery Compartment WTC blank cable penetrators with the ESC power cable penetrators yesterday and verifying that there was no loss of vacuum after one hour, I proceeded to do the long duration vacuum test of at least 20 hours.
This morning I again measured the vacuum level in the Battery Compartment WTC and found the level had dropped by only 20 mm Hg (1 mm Hg/hour) which was the same level loss after 20 hours when using the blank cable penetrators. Therefore I feel comfortable concluding that the 20 mm Hg vacuum loss over the 20 hours is probably due to my vacuum test setup and not the cable penetrators in the WTC End Cap.
Now I will move on to installing the ESC Signal cable penetrators in the Navigation Controller WTC End Cap and perform the same one hour and 20 hour vacuum leak test on that WTC.
More to come.
Regards,
Tom C AVD
Hi All,
I have some good news concerning the Battery Compartment WTC vacuum testing.
Up until yesterday the Battery Compartment WTC vacuum testing was being conducted with just blank cable penetrators as I was trying to ascertain the source of a 20 mm Hg/hour vacuum leak. Once I determined the source of the leak, which was due to the original universal cutoff ball valve, and installed a better quality ball valve designed for air compressors and vacuum pumps, I was ready to retest the Battery Compartment WTC with the actual T100 Thruster ESC power cable penetrators installed in the WTC End Cap.
I started by removing four of the blank cable penetrators and then cleaning the End Cap surface where each cable penetrator would mount and cleaning and re-lubing the O ring seal on each penetrator. I then installed the four T100 Thruster ESC power cable penetrators into their respective End Cap holes.
After verifying that all of the ESC power cable and blank cable penetrators were properly seated, I proceeded to pump down the Battery Compartment WTC to 560 mm Hg with the vacuum pump and then closed the cutoff ball valve to isolate the WTC from the vacuum pump. After waiting an hour I started the vacuum pump to bring the vacuum gauge back to 560 mm Hg and then opened the cutoff ball valve. Much to my relief the vacuum gauge did not move off of the 560 mm Hg mark indicating that the WTC had held the 560 mm Hg vacuum without leaking.
The fact that the installation of the ESC power cable penetrators in place of the blank cable penetrators did not result in any change in the ability of the WTC to hold a 560 mm Hg vacuum over the same one hour period as the blank cable penetrators indicates that the Blue Robotics cable potting process results in leak free cable penetrations into the Battery Compartment WTC.
I will measure the Battery Compartment WTC vacuum tomorrow after letting it sit overnight to see if there is any vacuum loss between this afternoon and tomorrow morning which will be around 20 hours.
More to come.
Regards,
Tom C AVD
Excellent news.
FYI, SeaBotix recommends testing at 10 in Hg for 10 minutes (page 13 here: http://www.seabotix.com/service_support/manuals/LBV200-4_manual.pdf ).
Hi bigkahuna,
10 inches of Hg is only 254 mm Hg. I am reaching 560 mm Hg which I consider to be a marginal vacuum level even though that was the best that I could obtain with my cheapie diaphragm vacuum pump.
I will probably investigate the purchase of a preowned oil filled vane vacuum pump to try and approach 760 mm Hg.
Regards,
Tom C AVD
Hi All,
Below are a couple of pictures of my WTC vacuum test setup. Originally I had the vacuum gauge between the WTC and the cutoff ball valve, but decided to move it to between the outlet side of the cutoff ball valve and the vacuum pump to help eliminate additional sources of vacuum leaks.
Therefore my setup starts with the vacuum pump, then a vacuum release valve followed by the vacuum gauge and finally the outlet end of the cutoff ball valve which is connected to the WTC through the 1/4" diameter barbed vacuum tubing adapter.
I begin the pump down process by starting the vacuum pump and then opening the cutoff ball valve. Once the vacuum gauge is indicating 560 mm Hg of vacuum I let the pump run for a while to help account for any residual outgassing of the tubing or components. The final step is to verify that the vacuum gauge is still indicating 560 mm Hg and then I close the cutoff ball valve which isolates the WTC from the vacuum pump, vacuum gauge, and the vacuum release valve.
After waiting an arbitrary length of time which initially was one hour, I start the vacuum pump again and wait until the gauge indicates 560 mm Hg of vacuum and then while watching the gauge for movement from the 560 mm Hg mark I open the cutoff ball valve. If the vacuum of 560 mm Hg in the WTC is holding, then there will be no vacuum differential between the vacuum pump line and the WTC.
So far I have not experienced any vacuum loss in the WTC after one hour, however I have seen a loss of 20 mm Hg of vacuum after approximately 20 hours after pumping the WTC down. I suspect that this minor loss of vacuum, which translates to ~0.01 mm Hg/minute, is probably due to my clunky test setup which is using inexpensive components, but will definitely identify a major vacuum leak due to faulty cable potting, nicks or cuts in cable jacketing, or O ring sealing.
I may run a two day WTC vacuum leak test to see if the leak rate is steady or begins to taper off with time which would indicate that the WTC and/or vacuum test components are still outgassing.
My present cheapie 12 vdc diaphragm vacuum pump can only attain a vacuum of 560 mm HG while 760 mm Hg is a complete vacuum. The more expensive oil filled vane vacuum pumps can reach a vacuum level in the very low millibar (<1 mm Hg) region if you want to spend the additional cash.
Regards,
Tom C AVD
Thanks Tom. A picture is worth more then a thousand words to me as I find I can understand what's going on a lot more when I look at a thing! It looks great. Looks like you have the leak well and truly on the run.
Just to clarify are you anticipating the ROV to be totally manually controlled or is there going to be some form of auto stabilisation? i.e. when you hit the forward thrusters if it pitches up slightly will the controller auto level or not at this stage?
Keep the great photo's coming!
Thanks, Grant.
Hi Grant,
Glad to be of help:-)
If you buy a better quality vacuum gauge than I have, I would recommend that you connect it in the line between the cutoff ball valve and the WTC to be able to continuously monitor the pumped down vacuum level of the WTC.
I plan to start with just the four Thruster configuration and manual control using the previously mentioned Top Side and ROV control board set and firmware developed by Nick Sopwith over on homebuiltrovs.com.
However Linus and I have been working on getting a BBBMINI setup working and plan to use it with a six Thruster configuration and use it to provide stabilization and dead reckoning guidance eventually.
Regards,
Tom C AVD
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