Assembling and Gluing the end caps
From OpenROV Wiki goooooooooood morning
Watch the video and assemble the endcaps. It is recommended to watch the video full screen and in HD to be able to see all the details.
External link: here
- Acrylic End Cap Pieces (3 Larger Clear Circles, 2 Smaller Clear Circles, White Circle, White Triangle)
- BD 1ml Syringe - ref 309628
The syringe is dual purpose. In addition to being a fairly low cost centering pin with good toleranceing and the ability to adhere to acrylic, it acts as a vent port for the tube. When the endcaps are placed into the tube, they compress the air inside the tube which causes the o-rings to seat in the wrong side of the gland (the gland is the name for the groove the o-ring sits in). If this happens, then when the ROV dives to a depth where pressure is equal to the compressed air in the tube (probably on the order of a meter or so below the water) the pressures on either side of the o-ring are equal and there is nothing to keep the o-ring sealed against the end of the gland, so it leaks.
Having a vent plug allows the user to equalize the pressure in the tube after closing the end caps so that the o-ring starts pressing against the correct side of the gland immediately when put under greater than 1 atm (sea-level) pressure. After placing the end caps on the tube, you pull the plunger out momentarily, listen for air to escape, then replace it.
The reason there are syringes on both end caps (only one is really needed for venting) is simply that it's easier to use the same parts for both.
(by Eric Stackpole)
- Acrylic Glue and Applicator
- Hack Saw
- Sand Paper - 150 Grit
- Stack the circular end cap pieces onto the syringe to give yourself an idea of the length of syringe. Notice the acrylic lines up to exactly 0.2ml, which is an important marker for the next step. The order is: solid then five clear--large, small, large, small, large.
- Use the hack saw to cut the syringe at exactly the 0.2ml line (make sure to remove the plunger). If anything, leave yourself a little extra space to sand down. The extra space should be on the side away from the tip and towards the plunger.
- Use a razor to debur the cut end of the syinge.
- Even and smooth the cut end of the syringe using the sand papaer, making sure not to go past the 0.2ml line.
- Add the first two clear acrylic circles (larger circle first, smaller second), making sure they are flush with the end of the outer part of the syringe (opposite side of the 0.2ml mark). Use the acrylic glue to weld the two circles, and syringe together. See this video for technique (although note that you should only glue one new circle at a time).
- Add and glue the rest of acrylic circles. (Order: Large Clear, Small Clear, Large Clear, Small Clear, Large Clear, White Circle.) Do them on one at a time, mimicking the technique shown in the video above. Make sure the white acrylic circle is firmly secured, as this one takes the most pressure in the process of pulling the caps off.
- Add and glue the white acrylic triangle.
- Make sure the second end cap mirrors the first. Like this:
- DO NOT glue the blue triangle on just yet. You'll want to wait until after you size and thread the tether/battery wire through the circle.
The end caps are the most important aspect of keeping the electronics tube dry, and the ROV functioning properly. A mistake in the endcap construction or application could result in a catastrophic failure of the ROV.
It's important that testing happen during and after the build, but also as part of a pre-dive checklist. Here's what to check for during assembly:
- Sizing OK - If you got the OpenROV kit or have laser cut the parts of the ROV yourself, it's important to double check that the end caps will fit securely into the electronics tube. After you add the o-rings to the endcaps, apply them to your extruded tube to make sure it fits securely. Important: It may be a good idea to sand the sharp edge of inner diameter of the electronics tube with medium grit sandpaper. This keeps the tube from damaging the o-rings during insertion. The tolerances for the extruded acrylic tubes is such that it might be too loose to work. Make sure it fits VERY tightly - you should be able to see the o-ring making a connection ALL THE WAY AROUND the tube.
- Water Test - It's a good idea to test the integrity of the electronics tube before you stuff it full of electronics. This test can be done after the epoxy application but before any electronics are wired up.
If you are concerned that the the endcaps are not fitting tight enough (and everyone should be monitoring this very closely) then you can add a strip of teflon tape around the endcap and slip the o-rings over the teflon tape. See below and repeat as necessary to get the desired, secure fit.