Hey All, Here are all the CAD files and some images of my new HDPE E-Can Endcaps


#1

Hey Everyone,

So, like many others when we received our OpenROV and assembled it water submergence testing showed a major amount of water leaking into the electronics can, I've said in other parts of the forum, but I am a Mechanical Engineering Student currently on a Work Term. Part of my work term has been helping some people here are the university in geography assemble their newly purchased OpenROV. Due to the fact that they don't have access to a shop, and by handing the ROV over to them when its completed I don't want there to be any chance of leakage I was wary of the Teflon tape / Latex balloon / Rubber bands solution. Initially tried Teflon and needed upwards of 5 layers on each side and still did not get a perfect seal.

I am also a member of our local International Competition level ROV Team, so I was familiar with endcap design, and O-Ring Design, and the shop I'm in had some spare 10 Pin Subconn connectors laying around (http://www.subconn.com/connectors/micro-series) to replace the epoxy potting.

Therefore, to solve the waterproofing issue I designed new endcaps in Solidworks to be manufactured out of HDPE. They allow for two 10 pin Subconn connectors ( one of the AUX wires is now just inside of the electronics can) which seal against the HDPE face with their own O-Rings. on the other end of the can I replaced the syringe with a swagelock fitting that simply seals with a M5 bolt, and when released releases the vacuum.

They were manufactured at our campus Technical services for about 60$ for the set, including one set of 1/8in O-Rings which were made in the shop out of 1/8 O-Ring Stock. We also got 4 spare rings made. they did them on a computer controlled lathe out of one solid piece of HDPE.

Some modifications were made to the chassis to accept the connectors
( just a couple of holes), nothing major!

They have been water tested for over 15 hours of submergence with no leakage whatsoever, but I haven't been able to test it with the ROV going yet, as we are still waiting for our batteries to arrive!

All in all, we are really pleased with them. It was also lucky to have the extra subconn connectors lying around. If we were to purchase the whole set ( two bulkheads and two connectors) it would have cost several hundred Dollars.

I have attached some pictures, as well as the solidworks files. If anyone wants a specific format let me know!

Nathan


1037-IMG_0493.JPG (381 KB) 1038-picturesOfNewEndcaps.zip (1.21 MB) 1039-SolidworksFilesNewEndcaps.zip (435 KB)

#2

This is awesome!!

We've been working on something similar in the lab. Now we just need to figure out a cheaper way to achieve the effectiveness of the subconn connectors. Eric has been showing me a few ideas he has using silly putty. Not sure if he's written about it on the forums yet...


#3

Hi Nathan,

I was happy to hear about the Subconn connectors...
until the price was "revealed"...
At "several hundred dollars" it will never be a viable option for me, unfortunately... :-(

Do you know what kind of equipment those connectors are usually used at,
for scavenging purposes... ;-)

Peter


#4

Nce work ¡¡

But ......

Appart from the correct adjustement of seals and Electronics Cylinder problems, which can be solved by latex or rubber bands, there is a structural one, which will end in a leakage, no mind how many bands could be fitted.

When external pressure pushes the tube, its middle section will always shrink more than the ends, which are supported by the internal disks of the end caps.

As that mid section diameter decreases, the shape of the E_tube, starts to separate from the cylinder, approaching a "diabolo like" one.

It means, that total pressure on the rubber seals, starts to get a non-ortogonal component, which angle grows with pressure. At the same time, effective mechanical pressure exerted by the tube on the external side of the O-ring seal, decreases, instead of increase.

Hence efficiency of seals becomes worse and worse with depth.

The more evident solution does not pass through making bigger, harder or more complex end caps, but, through limiting the E_tube central section shrinking.

Regards


#5

Placing the o-rings between the endcap and the edge of the e-tube worked for me to a depth of 230 meters. My biggest problem was trying to get the end of the tube smooth enough to make a good seal. I have solved that now, by cutting a disk from acrylic the same size as the edge of the tube and gluing it there. :) No more sore elbows from hours of filing/sanding.


The Blue ring in the first pic is the disk glued onto the end of the e-tube.


#6

Quite a nice work ¡

That final ring is the key. You've made pressure work for you instead of against.

For anybody information, here is a pic of a classic pressure hatch cover.

Congratulations and regards.