@Steve,
Thanks for the information and links, much appreciated.
The cable penetrators have three counter bores plus the main wire channel to the WTC side of the penetrator. All three counter bores are on the water side of the penetrator. The potting process starts with stripping about four inches of jacket off of the inner wires. The three counter bores and the wire channel along with the inner wires and the jacket area that will be potted are thoroughly cleaned with 91% isopropyl alcohol to degrease their surfaces. Then CA kicker is applied to the lowest level counter bore where the interface between the cable jacket and inner wires will be located. After the kicker dries, medium CA is applied to the jacket/wire interface and the cable is inserted into the lowest level counter bore. Once the CA has hardened, marine grade Loctite epoxy is injected with an industrial syringe a layer at a time into the second and third counter bores while the cable is wiggled around to help remove trapped air and allow the epoxy to settle to the bottom of the second counter bore.
After the epoxy on the water side of the penetrator has cured, the penetrator is turned upside down. Then the same marine grade epoxy is injected into the WTC end of the penetrator wire channel while the wires are wiggled around to help the epoxy move down the wire channel to achieve as much filling of the channel as possible.
The epoxy in the water side penetrator counter bores should prevent water (or air) from move along the outside of the jacket into the penetrator wire channel. The epoxy in the wire channel surrounding the wires hopefully will prevent either water (or air) from penetrating into the wire channel from the inside of the cable jacket.
Regards,
SSN626B/TCIII
Experimental ROV Design using Blue Robotics Components
Re: Experimental ROV Design using Blue Robotics Components
Hi All,
The 12 vdc vacuum pump came this morning courtesy of USPS and after about an hour I had it securely mounted on a wooden frame that I could clamp to my workbench because this pump is a diaphragm style pump and vibrates somewhat while in operation.
Never the less this pump can pull a 22 in (560 mm) vacuum, as stated by many of the reviewers of this product on Amazon.com, which is more than adequate for leak testing. So now I will try pumping down the battery compartment WTC to see hopefully find where the leak is coming from.
Regards,
SSN626B/TCIII
The 12 vdc vacuum pump came this morning courtesy of USPS and after about an hour I had it securely mounted on a wooden frame that I could clamp to my workbench because this pump is a diaphragm style pump and vibrates somewhat while in operation.
Never the less this pump can pull a 22 in (560 mm) vacuum, as stated by many of the reviewers of this product on Amazon.com, which is more than adequate for leak testing. So now I will try pumping down the battery compartment WTC to see hopefully find where the leak is coming from.
Regards,
SSN626B/TCIII
Re: Experimental ROV Design using Blue Robotics Components
Hi All,
All of you members who have bought the Blue Robotics T100 Thrusters with the built-in ESC can rest easy as I believe I have found where the leak is coming from on my first try with the new vacuum pump, but I do not know which of two components is causing the leak. Right now the WTC is holding at 540 mm Hg for without any vacuum loss.
Since this is the battery compartment WTC it only has the ESC power cable penetrator cables and the Aux power cable, to provide battery power to the navigation controller WTC. During my initial vacuum testing I had left the navigation controller WTC end of the Aux power cable penetrator at atmospheric pressure and the other end attached to the battery compartment WTC End Cap.
I had fabricated the Aux power cable and the cable penetrators exactly the same way that I had fabricated the ESC power cables and their penetrators using the same marine grade epoxy potting compound so I would assume that it should be as robust in relation to holding a vacuum as the ESC power cables. If it is defective, then I will have to fabricate a new Aux power cable with the new cable penetrators.
So I broke vacuum and removed one of the blank cable penetrators from the WTC End Cap and replaced it with the other end of the navigation controller Aux power cable penetrator that had been at atmospheric pressure. I then pumped down again and waited 15 minutes to find no loss in the WTC vacuum where as before I had lost 300 mm Hg over the same time.
The question that now begs to be answered is whether it is the Aux power cable and its penetrators that are leaking or is it a defective O ring on the blank cable penetrator that I removed to put the navigation controller end of the Aux power cable into the WTC End Cap?
The navigation controller Aux power cable penetrator is of the new penetrator design that holds the O ring captive in a groove cut into the back of the penetrator knurled head compared to the older cable penetrator design that holds the penetrator O ring stationary on the smooth part of the penetrator shaft by having the I.D. of the O ring being the same as the O.D. of the penetrator shaft. The blank cable penetrator is of the older design. However, the ESC power cable penetrators are of the older design also and do not appear to be leaking as the WTC is now holding a steady vacuum.
Obviously the next step will be to inspect the original blank cable penetrator for any O ring damage and then use it to replace the navigation controller penetrator end of the Aux power cable. If the WTC, after pump down, starts leaking again then it is most likely the Aux power cable or its penetrators that are leaking assuming the blank cable penetrator is not leaking.
Comments?
Regards,
SSN626B/TCIII
All of you members who have bought the Blue Robotics T100 Thrusters with the built-in ESC can rest easy as I believe I have found where the leak is coming from on my first try with the new vacuum pump, but I do not know which of two components is causing the leak. Right now the WTC is holding at 540 mm Hg for without any vacuum loss.
Since this is the battery compartment WTC it only has the ESC power cable penetrator cables and the Aux power cable, to provide battery power to the navigation controller WTC. During my initial vacuum testing I had left the navigation controller WTC end of the Aux power cable penetrator at atmospheric pressure and the other end attached to the battery compartment WTC End Cap.
I had fabricated the Aux power cable and the cable penetrators exactly the same way that I had fabricated the ESC power cables and their penetrators using the same marine grade epoxy potting compound so I would assume that it should be as robust in relation to holding a vacuum as the ESC power cables. If it is defective, then I will have to fabricate a new Aux power cable with the new cable penetrators.
So I broke vacuum and removed one of the blank cable penetrators from the WTC End Cap and replaced it with the other end of the navigation controller Aux power cable penetrator that had been at atmospheric pressure. I then pumped down again and waited 15 minutes to find no loss in the WTC vacuum where as before I had lost 300 mm Hg over the same time.
The question that now begs to be answered is whether it is the Aux power cable and its penetrators that are leaking or is it a defective O ring on the blank cable penetrator that I removed to put the navigation controller end of the Aux power cable into the WTC End Cap?
The navigation controller Aux power cable penetrator is of the new penetrator design that holds the O ring captive in a groove cut into the back of the penetrator knurled head compared to the older cable penetrator design that holds the penetrator O ring stationary on the smooth part of the penetrator shaft by having the I.D. of the O ring being the same as the O.D. of the penetrator shaft. The blank cable penetrator is of the older design. However, the ESC power cable penetrators are of the older design also and do not appear to be leaking as the WTC is now holding a steady vacuum.
Obviously the next step will be to inspect the original blank cable penetrator for any O ring damage and then use it to replace the navigation controller penetrator end of the Aux power cable. If the WTC, after pump down, starts leaking again then it is most likely the Aux power cable or its penetrators that are leaking assuming the blank cable penetrator is not leaking.
Comments?
Regards,
SSN626B/TCIII
Re: Experimental ROV Design using Blue Robotics Components
SSN626B,
I haven't been monitoring this site as regularly lately. I was elated to see yet another detailed thread on a build. Your design looks great and you're doing fantastic work!
Your vacuum tests are interesting to me. I haven't looked up how the vacuum measurements equate to depth yet, and thought about something similar, but ultimately decided to go with building a hydrostatic chamber instead. Many of the o-ring specs are similar for water and air, and the differences are probably negligible at lower pressures.
I just tested my chamber a week ago and got it up to 500 psi, with room to go higher! The safest/easiest way to actually get to that pressure is with water. That's over 1000 feet deep which is much deeper than my target of 300-400', but I wanted to add safety factors in to it. I also wanted the ability to more easily test multiple through hull penetrator designs, different hulls (potentially), and peripheral components (light housings, actuators, etc). I figured a chamber would be the way to go. I've got one of the aluminum through hull penetrators from Blue Robotics, but haven't tested it yet. Certainly will down the road but I am designing a penetrator similar to what SVSeeker put together, with a little twist. I need lots and lots of connections...
Anyway, props to you on moving so fast on your project. I'm sure you've been planning a lot, but looks like quick progress on building. It'll be fun to see what you get put together, and I appreciate you taking the time to share. In time, I hope post some pictures and design details on the hydrostatic chamber and maybe offer to other ROV enthusiasts a way to test their products (with video) if they are not up to building one on their own.
Keep up the good work!
I haven't been monitoring this site as regularly lately. I was elated to see yet another detailed thread on a build. Your design looks great and you're doing fantastic work!
Your vacuum tests are interesting to me. I haven't looked up how the vacuum measurements equate to depth yet, and thought about something similar, but ultimately decided to go with building a hydrostatic chamber instead. Many of the o-ring specs are similar for water and air, and the differences are probably negligible at lower pressures.
I just tested my chamber a week ago and got it up to 500 psi, with room to go higher! The safest/easiest way to actually get to that pressure is with water. That's over 1000 feet deep which is much deeper than my target of 300-400', but I wanted to add safety factors in to it. I also wanted the ability to more easily test multiple through hull penetrator designs, different hulls (potentially), and peripheral components (light housings, actuators, etc). I figured a chamber would be the way to go. I've got one of the aluminum through hull penetrators from Blue Robotics, but haven't tested it yet. Certainly will down the road but I am designing a penetrator similar to what SVSeeker put together, with a little twist. I need lots and lots of connections...
Anyway, props to you on moving so fast on your project. I'm sure you've been planning a lot, but looks like quick progress on building. It'll be fun to see what you get put together, and I appreciate you taking the time to share. In time, I hope post some pictures and design details on the hydrostatic chamber and maybe offer to other ROV enthusiasts a way to test their products (with video) if they are not up to building one on their own.
Keep up the good work!
Re: Experimental ROV Design using Blue Robotics Components
I might be off here, but I think the most dept you can simulate using a vacuum is 1bar or 10m depth.
When you make a vacuum, you pump the air out of a sealed container. Once all the air is out you have 100% vacuum.. witch is only possible in theory I believe. Once there is no more air to pump out, there is nothing more to gain as there is nothing ore to remove from the container. The force acting on the sealed container with the vacuum in it would then be the one bar atmospheric pressure from the outside.
So the differential between the inside and outside of the container will be 1 bar.
Correct me if I'm wrong.
When you make a vacuum, you pump the air out of a sealed container. Once all the air is out you have 100% vacuum.. witch is only possible in theory I believe. Once there is no more air to pump out, there is nothing more to gain as there is nothing ore to remove from the container. The force acting on the sealed container with the vacuum in it would then be the one bar atmospheric pressure from the outside.
So the differential between the inside and outside of the container will be 1 bar.
Correct me if I'm wrong.
Re: Experimental ROV Design using Blue Robotics Components
@olegodo,
Yes, you are correct.
The pressure in an enclosed vessel is due to the Brownian Motion of the molecules of air in the vessel which is temperature dependent (PV=nRT).
Once all of the air is evacuated, then there are no longer any air molecules bouncing off the inside of the vessel.
Since all materials outgas, a 760 mm Hg vacuum cannot be maintained until all of the components within the vessel have outgassed which requires continuous pumping until the outgassing is complete.
The real test of water tightness would be to put the WTC into a chamber filled with water and pressurize the chamber until the pressure outside the WTC is the same pressure the WTC will be operating at in its operating environment.
Regard,
SSN626B/TCIII
Yes, you are correct.
The pressure in an enclosed vessel is due to the Brownian Motion of the molecules of air in the vessel which is temperature dependent (PV=nRT).
Once all of the air is evacuated, then there are no longer any air molecules bouncing off the inside of the vessel.
Since all materials outgas, a 760 mm Hg vacuum cannot be maintained until all of the components within the vessel have outgassed which requires continuous pumping until the outgassing is complete.
The real test of water tightness would be to put the WTC into a chamber filled with water and pressurize the chamber until the pressure outside the WTC is the same pressure the WTC will be operating at in its operating environment.
Regard,
SSN626B/TCIII
Re: Experimental ROV Design using Blue Robotics Components
Hi All,
Rusty and I are still troubleshooting the 20 mm Hg/hour vacuum leak that I am experiencing with my Battery Compartment WTC.
Today I went to Home Depot and purchased an air compressor cutoff ball valve and used it to replace my present universal cutoff ball valve to see if the leak is being caused by the ball valve.
I presently believe that the leak is not in the WTC and needs to be isolated to a component /connection in the vacuum test setup.
More to come.
Regards,
SSN626B/TCIII
Rusty and I are still troubleshooting the 20 mm Hg/hour vacuum leak that I am experiencing with my Battery Compartment WTC.
Today I went to Home Depot and purchased an air compressor cutoff ball valve and used it to replace my present universal cutoff ball valve to see if the leak is being caused by the ball valve.
I presently believe that the leak is not in the WTC and needs to be isolated to a component /connection in the vacuum test setup.
More to come.
Regards,
SSN626B/TCIII
Re: Experimental ROV Design using Blue Robotics Components
Hi All,
It looks like I have identified the source of the vacuum leak in my Battery Compartment WTC vacuum test setup.
As I stated previously I had purchased a cutoff ball valve that was specifically designed for compressor/vacuum systems. I used the new ball valve to replace my existing universal cutoff ball valve in the vacuum test setup. After pumping down the WTC to 560 mm Hg I closed the cutoff valve and waited half an hour before checking the vacuum gauge which had stayed at 560 mm Hg.
So far so good. So I opened the cutoff valve after starting the vacuum pump and the vacuum gauge did not move off the 560 mm Hg mark. So I waited for an hour this time and then checked the vacuum gauge which again had not moved off of the 560 mm Hg mark. So it looks like it was the original universal cutoff ball valve that was leaking air back into the WTC after the pump down.
Now I can move on to completing the assembly of the Battery Compartment WTC and then move on to the Navigation Controller WTC assembly.
More to come.
Regards,
SSN626B/TCIII
It looks like I have identified the source of the vacuum leak in my Battery Compartment WTC vacuum test setup.
As I stated previously I had purchased a cutoff ball valve that was specifically designed for compressor/vacuum systems. I used the new ball valve to replace my existing universal cutoff ball valve in the vacuum test setup. After pumping down the WTC to 560 mm Hg I closed the cutoff valve and waited half an hour before checking the vacuum gauge which had stayed at 560 mm Hg.
So far so good. So I opened the cutoff valve after starting the vacuum pump and the vacuum gauge did not move off the 560 mm Hg mark. So I waited for an hour this time and then checked the vacuum gauge which again had not moved off of the 560 mm Hg mark. So it looks like it was the original universal cutoff ball valve that was leaking air back into the WTC after the pump down.
Now I can move on to completing the assembly of the Battery Compartment WTC and then move on to the Navigation Controller WTC assembly.
More to come.
Regards,
SSN626B/TCIII
Last edited by SSN626B on Oct 21st, 2015, 5:42 pm, edited 1 time in total.
Re: Experimental ROV Design using Blue Robotics Components
Hi All,
For those of you who will be checking your WTC for its water tight integrity using a vacuum pump, please find attached a useful document that may help you distinguish a true vacuum leak from an outgassing induced vacuum loss.
Regards,
SSN626B/TCIII
For those of you who will be checking your WTC for its water tight integrity using a vacuum pump, please find attached a useful document that may help you distinguish a true vacuum leak from an outgassing induced vacuum loss.
Regards,
SSN626B/TCIII
- Attachments
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RateofRise Curves-Diagnostic Tool.pdf- (30.96 KiB) Downloaded 317 times
Re: Experimental ROV Design using Blue Robotics Components
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.
The Cutoff Ball Valve has a red handle while the Vacuum Release Valve has a knurled knob
The Vacuum Pump is to the right of the black Vacuum Gauge
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,
SSN626B/TCIII
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.
The Cutoff Ball Valve has a red handle while the Vacuum Release Valve has a knurled knob
The Vacuum Pump is to the right of the black Vacuum Gauge
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,
SSN626B/TCIII