Brushless motor

[leeinmt]

Now that I got the thrusters figured out with flex shaft drive, I'm trying to solve how to get the 12 motor power wires through the rear pressure vessel bulkhead to the ESC's inside.
Some of the other threads here address this with some impressive efforts, but I need mine to be leakproof to 500' depth (300 PSI).
I'm leaning towards a small oil (or alcohol) filled compartment that has female barrel connectors potted in epoxy and reinforced with a brass rod grid and is sealed to the outside edge of the bulkhead with double o rings. The individual wires from the motors enters this chamber from the outside through tight fitting o-ring seals and plug into the potted recepticals.
If I think about this long enough (and steal other folks' ideas), maybe a light bulb will light up.
This should probably be addressed in another thread dealing with pressure hulls, etc.
Sorry if drifting off topic.

[bikerbones1968]

Sounds like an impressive system lee. Hope you can post some photos for us to look at.

I have tested my potted connections to 200' without issue. I am unsure if my 6" schedule 80 rigid PVC hull could withstand the pressure at 500' depth.

Would it be possible to fill the entire hull with non-conductive oil? It would be messy if you have to take it apart for repairs though. How are your GoPro's going to survive at that depth? I know my GoPro dive case is only rated to 197' .

[leeinmt]

I'm almost done with the thrusters and will post photos then. The ESC's and cameras will be inside the pressure hull with their wiring exiting through the rear bulkhead.
Hydrostatic testing of the pressure hull will tell me what I can get away with depth wise. I am hoping to enclose the cameras, sensor electronics, ESC's, and two gel-cell batteries within. But how to do the hydrostatic test to 4 or 500 psi of external pressure?
Filling the pressure hull with oil would subject these (and other) electronics to the outside ambient pressure and could damage them at the component level.
Your (Biker) description of hard wiring the JR radio really got this project off the ground. So much easier with intuitive joysticks than the old model RR DSS system I used on my first ROV.

[scubersteve]

How would filling the hull with oil expose the components to outside pressure?
It might expose them to a small amount of pressure as the hull tries to compress under the load of the pressure outside but with a small amount if air inside with the oil(which you would have anyway) the pressure inside should be fairly low.

[rossrov]

Lee, short of building a potentially lethal pressure test tank, and charging with water NO AIR AT ALL, consider doing a real-life test but with minimal componentry on board. Cheap camera looking at the inside of the pressure hull and an LED, and some deep water.
Before going out in the boat, you can simulate low depth by pulling a vacuum on the inside of the pressure hull. I did this using a fridge compressor working as a vacuum pump. I could see into the camera pressure hull through the camera window (no cam fitted) and the ESC and battery hull had an inspection window so I could see in there as well. Can do in air with some soapy water inside the hull around the seals and look for bubbles, or dump the hull into a bucket of water. At best will give you 10 metres, but a good way to do a preliminary test. This method is potentially hazardous as well so wear safety glasses at least.
Open and close the pressure hull and repeat the test several times so you can be confident that the last time you close it up with all the goodies inside it wont leak!

[leeinmt]

I used to own an 1899 Stanley Steamer classic car and we did hydrostatic testing on the boiler up to 800 psi. As you say, the vessel has to be completely filled with water or it can catastrophic. The original Stanley boilers were fire tube and wrapped in three layers of piano wire. The tubes would fail before the main boiler body. We typically ran the thing at 400 psi live steam and it would outrun a Corvette.
If I can't find an adequate testing tank, I will have to go to the lake and drop it down to the max 425 foot depth.
However I test it, it will be empty except for the wiring connectors and a water alarm.
External pressure is so much different than internal on a cylindrical shape.
If a hydrostatic test tank fails, you get a little squirt instead of a kaboom.

Lee

[rossrov]

Fire-tubes a good analogy. Folks here have done some interesting stuff before!

[leeinmt]

I've figured out how to pressure test the hull, but I am going to take it over to the 'frames and hulls' thread so it won't be off topic.

Lee