Oil compensation of electrical and motor housings


#1

I know I'm new to the site and I may have missed this. Have you guys looked into compensating the electrics? Sub Atlantic compensators The concept is to use mineral oil in the enclosure, and have a spring loaded bladder filled with oil attached. This keeps a positive pressure by a few PSI in the enclosure and any leaks go out, not in. It keeps you from having to build a beefy enclosure to withstand pressure. The downside is, the components see ambient pressure plus whatever is produced by the comp spring. It makes it messy to work on, but that's how the industry does it.

The commercial ones I linked to cost an arm/leg, but they are not rocket science to throw together. A length of tygon coiled up works, and is used on some subsea torque tools I use.


#2

I was thinking the same thing, just made a comment at /. about it. I don't think you need the whole compensator assembly for the design depth. I think just an oil fill would work to massively increase the structural strength since it would less compressible than air. Oil alone would also be good for the seals. Oil would probably be an issue for camera optics and the CCD.

I was also playing with the idea of just resin or rubberized undercoating all of the electrical components and skipping the sealed cylinder altogether. That would leave the camera as the only problem part.


I think a camera sourced from as a cell phone replacement part would stand the best chance at being a fully sealed enclosure, but I bet there are other options with less work needed to interface.


#3

It's an interesting idea and we've definitely looked into it. The biggest issue is keeping the simplicity up and the cost down. Earlier on I also designed a magnetically coupled drive which didn't require a stuffing box or other waterproof mechanical pass-through at all. Once avian though, it proved to be to expensive and complicated to build for what I was targeting. In the end, brushless hobby motors like the ones we are using seemed to be the best because there is nothing to waterproof as long as corrosion and electrical shorting can be taken care of. We're still perfecting how to do this (and could use input) but things seem to be working well so far.


#4

Just throwing out some other off the wall propulsion ideas. The DC brushless approach is by far the best even if they end up having some kind of replacement cycle due to wear.

Submersible pond and fish tank pumps are already made potted. They have the major draw backs of probably using too much current and producing too little torque, especially with the larger impeller that would be need to be mounted. They also need AC current, but you are already headed that direction. I suppose with some ability to change the AC frequency, you could get more push from such an induction motor.


Depending on what kind of wave patterns, frequencies, voltage range, and power an I/O board like Arduino could put out, one might be able to fashion something similar to the so-called Dyson Digital motor using off the shelf air core inductors placed on an iron core armature and potted / resin filled throughout. The motor is essentially a half-breed between AC induction and DC brushless.

A hydrostatic drive coupling / torque converter would probably be easier to use, but the smallest ones I can think of are for riding lawnmowers. Similarly, a pneumatic or hydraulic drive system would add unnecessary complication.

Last crazy idea. Voice coil and armature from a computer HDD. Proper frequency input and a fin and it can swim like a fish. Actually, any sealed voice coil has interesting possibilities. Why yes, that is the sound it makes at full speed.

By the way, are you potting the excess space inside the DC motor casings? That would add some level or corrosion resistance in case the winding insulation reacts poorly to salt water as well as insulating solder junctions. I know I heard something about an added water proofing coating, but wasn't sure what procedure you are going with.


#5

all our cameras are 1 atm housings and expensive. Anyone tried forming plexiglass with hot oil? You can make 2 half domes with a gasket seal. A friend of mine did this to make camera housings for scuba diving.


#6

forget AC. go direct with building a DC brushless controller. it isn't terribly hard, there are plenty of designs and software for them on the web.


#7

I am just wondering why you say forget AC and go DC ...

Why wouldnt steppers work.... I understand for this application there is literally no need for positional control in like a stepper motor, but ... ya, I guess I'm wondering why you are totally against AC, or just for this application?


#8

Stepper imho is still a DC system. by AC I meant 120v 60hz. submersible fish tank and pond pumps are pretty much all designed to be 120v 60Hz motors. You can't change the speed. You most of the time can't change the direction. Being submersible and already waterproofed is the only thing they have going for them.