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Tether Quick Disconnect


(Mark Langille) #1

Has anyone tried or used a quick disconnected waterproof fitting between the tether and BlueROV?

Is there any technical reason one isn’t used more commonly, ie issues with the twisted pair transmission or similar or more a cost issue?

Would be nice to be able to easily remove the tether from ROV for transport, etc.


Tether quick connect?
(TCIII) #2

@schoonerlabs,

I think that one of the biggest issues with the four twisted pair tether is the cost and complexity of an inline waterproof connector. They are definitely not cheap by any stretch of the imagination and the multiple pin connections can lead to reliability issues.

Rusty’s move to the Fathom X interface greatly reduces the cost and complexity of an inline waterproof connector since it requires just a twisted pair for the tether, but this interface will presently not work with a serial interface like the Fathom S which requires two way duplex transmission. Also the Fathom X interface requires an onboard computer such as the RPi to handle the UDP communication compared to the Fathom S interface.

Decisions, decisions!

Regards,

TCIII AVD


(Kevin) #3

I used the Seacon Micro Wet-con series on my earlier OpenROV modifications with very good results. Yes, they are expensive, but in this business you get what you pay for.

I have an 8 pin set that is ready to install, just haven’t had the time to do it yet. The cable thimble would be attached to an aluminum caribiener clip an that would be attached to the frame.

http://www.amronintl.com/seacon-micro-wet-con-inline-connector-male-8-pins-mcil8m.html?___SID=U


(Paul) #4

Seacon is what most of the ROV industry swears by. Problem is that they are (in my opinion) over kill and expensive. Most of the time we don’t really need to “wet disconnect” connectors, we just need a connection that is made while topside to stay dry while at depth. Some of the smaller ROV manufacturers have gone to “dry connect” bulkhead connectors not meant for the subsea industry, but rather other industries (like chemical instrumentation). The question is, where do they find them?

I’ve been testing some of the connectors that are advertised as “waterproof” and sold on eBay. So far these are the best I’ve found, but I haven’t tested them to any deeper than a couple of feet. Cost was a couple a dollars a set.



(Rusty) #5

@schoonerlabs,

There isn’t a technical reason that we don’t use a quick disconnect. It’s purely cost at the moment. Most depth-rated 8-pin connectors are very expensive, like $150/set.

It’s definitely important and a good connector will improve the usability of the ROV pretty significantly. If you’d like to get something right now and you’re using the Advanced ROV Electronics Package, then I’d recommend looking for 2-pin connectors, since that’s all you really need for Fathom-X. There are some available from Subconn and Seacon, like the MCIL2. You can purchase those at amronintl.com.

We’re working on a better long term solution, but connectors are hard!

-Rusty


(Pierson) #6

Brad Harrison connectors also work and are slightly less costly, used them for something like 12 years on an AUV, not sure how well they transmit signals we always got away with it but might not work in every application. http://www.bradharrisonsales.com/select_se_mc.htm


(Paul) #7

@Pierson - Those Brad Harrison connectors look a lot like what I used in a ROV build a long time back. Couldn’t remember where I found them. Do you remember how deep you took them to? The eBay connectors I bought are very similar but as yet untested to any real depths.


(Richard) #8

@Rusty-I know you guys are experts on O-ring sealing.

Is it possible to get a good seal with decent O-ring life if the O-ring remains in moving contact with the sealing surfaces as it is compressed by rotation? For example, how well does an O-ring seal bolt threads when installed under a hex bolt head that is being torqued down in rotation (screwing into threads)? I ask because this is related to finding a solution for an inexpensive connector.

Thanks,

Richard


(Pierson) #9

@paul that vehicle was always less than 30 ft, never had any connector leaks, After 10 years the electrical connections got a little inconsistent but truly incredible shelf life for it with little to no maintenance and no shortage of abuse.

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The connector design as used in your Ebay connector and these Brad Harrison connectors, where the gasket is between two body pieces held in compression by a threaded ring is fairly common. I have seen it, at a deep sea ROV company, in some SeaConn and SubConn connectors, and many other more expensive professional underwater connectors, in applications up to and including 1000+ meter depths. Of course much of it is in the details of the construction but the design has a lot of potential. Additionally compared to the other design of the more affordable connectors, which are molded silicone, it seems easier to manufacture without specialized tools.


(Pierson) #10

In my experience endurance gets worse with smaller diameter and cross section. I would be really interested in seeing a test of 3XX-4XX cross section o-rings those have enough flex and toughness probably could do quite a few sealing-unsealing cycles, on the other hand over tightening could drastically reduce that, and on a smaller diameter the rotational torque may be amplified by the typically finer threads. A Lot of variables at play. Would be really interesting to see any hard data on that type of endurance. My only thought is there might be something on it in the valve literature.


(TCIII) #11

Hi All,

Here is a discussion thread on the OpenROV Forum concerning the more inexpensive waterproof connectors.

Regards,

TCIII AVD


(TCIII) #12

Hi All,

For a single twisted pair Tether you might want to consider this two pin waterproof connector on Amazon.

For the Fathom Tether you might want to consider this eight pin waterproof connector on Amazon.

Based on the OpenROV connector discussion thread the two pin waterproof connector was tested down to 208 meters without leaking. I think these connectors are only as good as the O rings and it might be possible to buy better quality O rings of an equivalent size.

The bottom line here is you get what you pay for. More expensive connectors will perform better over the long run. However since I will not go below 100 feet (33 meters) I can probably get away with using the cheaper connectors.

Regards,

TCIII AVD


(david) #13

I have some of these from Adafruit I tried them anyway and not happy with the results. I never had an actual leak but when I unplugged the connectors when back on the surface the pins were always damp.

 

Having said that, they are only rated for IP67 so I can’t blame them for not performing more than they are designed for


(Richard) #14

I am working on a quick disconnect design. Anyone see an electrical problem with using an 8-pin Mini DIN for the electrical connection?


(TCIII) #15

@Richard,

The DIN connectors that I have worked with have minimal contact area between the male and female pins and to the best of my knowledge are not gold plated and might eventually corrode.

Regards,

TCIII AVD


(Michael) #16

There would certainly be utility associated with a robust inline disconnect for the umbilical. It would be worth $120 - $150 to me at least for the cost of reliable underwater connectors. I sent an email to MacArtney, the company that manufactures SUBCONN connectors. Here’s a response I received from their PacNW manager… Note the issue he raises re: the jacket on the BR2 umbilical being polyethylene. Polyethylene seems to be stronger than polyurethane. I currently have a polyurethane umbilical for a sidescan sonar. It is much softer than the jacket on the BlueRobotics2 umbilical. In field use, it is easy to tear/nick, etc.

Has anyone found a good PE-compatible connector body?

===============================

Hi Mike,

Thanks for thinking of us.

Our Subconn Micro series bulkhead & inline connectors may be a good option for being able to remove the tether from the vehicle. Here is a link to the product line:

However the cable spec shows a Polyethylene jacketed cable. We can’t mold to that material. We can mold to a Polyurethane (PUR) jacketed cable. Is there any way that you can consider an alternate tether? If so, we can likely find and price out a PUR tether for you.

Please let me know.

Thanks,

Don Bryan

General Manager

 


(Rusty) #17

Hi Michael,

We’ve spent quite a bit of time talking to the Subconn folks as well. The $120-$150 range is about what you’d have to spend to get an 8 pin connector from them. If you’re using the Advanced Electronics with the Fathom-X board, then you technically only need 2 pins in the connector, which can reduce the price substantially.

Most pro ROV tethers that I have see use a polyethylene foam jacket. The only problem with it is that polyethylene doesn’t adhere to most potting compounds very well. We’ve had good luck with sealing the tether in our cable penetrators using a few different types of epoxy. We’ve also tried adding a length of heat shrink over the tether first. The heat shrink acts like an O-ring seal and provides a better surface to adhere to.

We’re planning to have a suitable connector available within a few months, just FYI.

-Rusty


(Mark Langille) #18

Rusty - Is there nay chance you might be able to source a small inventory of 8 wire connectors for the short term for customers to use as an option? Might be easier as a group buy. I’d be interested in something I could buy direct from BR for now even if not ideal long term. Just a thought.


(Rusty) #19

@schoonerlabs - We’ve thought about it and have the quotes ready to do that. The part I’m concerned about is the splicing from the tether to the connector pigtail. As I mentioned above, it’s a relatively difficult process. We’re working on a solution that will not involve splicing to the cable.

Thoughts?


(Mark Langille) #20

The connection to the existing tether is one of our concerns as well but will need to have a solution for existing owners of some sort I suspect and least for shorter term. Properly soldering, wrapping, and potting it to water seal I guess will be the approach.