modular ROV concept

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A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

goopypanther wrote: A gasket will likely be more simple to design...Gaskets will also have more contact area than a thin O-ring would which will probably produce a better seal under high pressure if you've clamped it in right.

One alternative to having many complicated and failure prone watertight joints between cubes is making each unit self-contained. Each cube could have its own battery and communicate wirelessly (even underwater, the other device is only on the other side of a plastic bulkhead). The batteries could even be trickle charged through inductive power transfer.
I really am leaning towards a gasket, for simplicity, cost, and effectiveness, also there is no design penalty for using one instead of o-rings!
I really like that wireless-cube idea, it would significantly increase the cost of the project but it would also make it more robust; something it needs to be successful in the long run!...do you have any experience in doing something like you described? I am inexperienced with R.C. stuff so any knowledge you could pass on would help.

Does anyone have a good alternative to M2 screws? the size of the screw head can't really be larger than 4 mm.
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TigerShark
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Location: Washington State

Re: modular ROV concept

Post by TigerShark »

I would recommend not using a gasket, I had major issues with a gasket leaking over using O-rings which are much better at sealing under pressure. You don't want a lot of surface area as it is harder to compress it enough to get a good seal. Take a look at professionally designed housings, they use O-rings. You want the pressure to work for you to increase the seal and in my experience pressure wanted to separate the gasket from the sealing surface.
Jaman42
Posts: 94
Joined: Nov 3rd, 2014, 4:19 am

Re: modular ROV concept

Post by Jaman42 »

"frame is milled UHMWPE"

Have you considered casting the frames instead? Would be a whole lot of milling wouldn't it? And pretty much waste, if you take your time and make a good mold with all the grooves in place you would have a finished piece straight out of the mold. You might have to redesign them a bit for that to work thou. Also I have read that milling grooves (if you take take that route) can be quite tricky since it will often leave small scratches letting water sip thru the o-ring. When you use a lathe to make a grove on a circular work piece all the little scratches goes in the same direction as the o-ring so it wouldn't affect the seal.

If you aren't casting the frames you could perhaps use a design with circular plates instead so that you can use a lathe to machine the grooves.

"for simplicity, cost, and effectiveness", those are all true for o-rings

In the exploded view it looks like a groove but perhaps it isn't? If it is, I believe the bolts are on the wrong side of the seal.
A.R.E.S._R.O.V.
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Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

In the drawing there are grooves for o-rings, they were originally what I planned to use because i had them on hand already, I am getting a lot of mixed responses from people on which to use.

Jaman42: I don't have the equipment or know-how to make molds or melt plastic to fill them, would that be a service you could provide? (Is it cheaper than my current cost or materials which are ~$500). I am blessed enough have CNC mills and lathes available to me free so my only cost is the bricks of plastic.

Which side of the seal should the bolt holes be on? I put them inside the groove because the inside behind the holes is recessed with a keyseat cutter for a nut if I move the hole too far outwards then the holes would not have enough clearance with adjacent nuts on other faces of the cube. (see picture)

goopypanther: after talking about the independent wireless cube idea with some "experts" I have decided that it exceeds our budget and would likely be too complex to make sense on a small scale project like this. I will keep this in mind for future improvements though because it's a great idea in concept.
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Jaman42
Posts: 94
Joined: Nov 3rd, 2014, 4:19 am

Re: modular ROV concept

Post by Jaman42 »

I'm just learning about casting so I won't be much help there, I find it interesting thou. If you buy some sort of resin to cast with I believe it would get quite expensive at least here in Sweden. There are methods where you can buy plastic pellets, melt and use in a injection mold. The injection mold complete with the injection and melting system would be quite costly to make I would say but the plastic used for every part would be very cheap. I'm interested in the idea to make a reasonable priced injection molding system, time will tell if I make anything of it.

Wrong side was a bit poorly worded perhaps, since with the current design the hole will make it in to the water tight container anyways. If you put them on the inside, each of the bolts must be completely waterproof. If you put them on the outside and make a design where the holes never penetrate the water tight container then they wouldn't have to be waterproofed. That's probably a better explanation of what I meant :)
A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

Jaman42 wrote: Wrong side was a bit poorly worded perhaps, since with the current design the hole will make it in to the water tight container anyways. If you put them on the inside, each of the bolts must be completely waterproof. If you put them on the outside and make a design where the holes never penetrate the water tight container then they wouldn't have to be waterproofed. That's probably a better explanation of what I meant :)
Jaman42 wrote: If you aren't casting the frames you could perhaps use a design with circular plates instead so that you can use a lathe to machine the grooves.
I'm pretty sure I know what you mean! I'll draw up some designs and see how they work logistically. I've decided against casting, I called a friend of mine who works with casting and he said it would be prohibitively expensive. As far as the circular plate thing, I really like that idea. It seems like it could help solve a lot of manufacturing issues I was facing. thanks!
A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

I just purchased a small bit of plastic. I'll be milling out one face of one cube with all the bolt holes and seal. This way I can test the waterproof-ness of the system. I'll post an update once I have the plastic!
A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

here is a schematic for the test cube face:

The o-ring groove is 0.712mm deep, and i'll be using a #042 o-ring.

I put three holes so that I could test weather just having four screws (one in each corner) would be sufficient, or if I needed eight (two in each corner).
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A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

Here is my latest update after a lot of development: I have almost all of the cubes done; I ended up going wit 3/8" polycarbonate sheet which I CNC cut and chemically welded together for waterproof-ness and strength. Then I used 1/16" silicone sheet with a 40A durometer rating as a gasket for all of the cubes. The motors are mounted with a 3D printed structure into cubes with two faces missing so water can flow through freely. More updates to come :D
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Here is the battery I'm using
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A.R.E.S._R.O.V.
Posts: 20
Joined: Nov 23rd, 2015, 4:27 pm

Re: modular ROV concept

Post by A.R.E.S._R.O.V. »

Hello fellas, life has gotten in the way of my ROV project for the last year but recently I've been able to put some work in. I am still pursuing the modular cube design. I like it because it allows me to adjust my design based on what I need at the time. In my current place I can't afford to finish the current designs with 12+ cubes, so I'm am now focusing on a 5 cube design as a proof-of-concept. Here is the configuration I'm using, and the wring diagram (excluding lights or camera setup). I have the standard three-thruster setup, the arduino/esc's will be in the front chamber, and the batteries will be in the back section.
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