Tether buoyancy idea.

[Pilikia]

Paul ~ You misunderstood me. I am in no way criticizing your idea. To the contrary, I think it is a good one. I'm just suggesting that in the design of these little capsules, especially the shape at their ends and how they grip the tether (subjects not yet discussed), deserves some study to minimize the chances of them hanging up on each other.

[Carlos D]

Paul, you're absolutely correct, this is a HOBBY, we're not commercial ROV builders. I believe
your pvc capsule design is less likely to hang up than foam ones, besides, all the postulating
in the world won't solve the issue. It comes down to design and testing, tweeking out the
kinks (no pun intended), retesting ,etc. Those of us that have built ROVs have been down
that rocky road many times. Let me know how things turn out, good luck!

[PaulC]

Pilikia I am sorry if I seem to have taken it the wrong way. I agree with everyones comment about the "Hang Up's" or the possibilities of hang ups. If anyone out there has any ideas about the shape of the capsules I am open to ideas. Maybe, if we all work together on this one we might just be able to all benefit. Things to remember about this we need it to be rather low cost, rigid, of course no hang ups if possible, I also think that most if not all materials need to be "off the shelve" so to speak. And if anyone has any ideas as to how long to make the tube portion of the capsule that would be great. I was thinking right of the cuff that it should be about in overall length including the caps should be 2 1/2 or 3 inches. I guess some serious testing is in order.

[Pilikia]

Something like this might work...

[PaulC]

Hey Pilikia,
Did you just heat it up and squish the ends, and if so is it watertight?

[Pilikia]

yes, in kitchen oven preheated to 250 for 15 minutes. Holes were pre-drilled and pipe cut axially with hacksaw to a depth just below the holes. Each clamp was two 2" x 5/16" fender washers and bolt with wingnut. I took it out of the oven, clamped one end, put it back in the oven with clamp on it to resoften the pipe, then took it out to clamp the other end with another clamp.

Is it watertight? Ummm... It does float, and I don't hear any water sloshing around inside it. Haven't taken it to depth. My intent is to put a little "worm" of epoxy clay behind the bolt, which will then be squished out while clamping to seal it. For this test, I didn't try including the epoxy clay. I just wanted to get the forming technique down.

I'm surprised how little buoyancy it offers. I think Steve's observation that schedule 40 is heavy, and a bit overkill is a good point. Today I am trying it using 1" class 200 PVC pipe. It has a much thinner wall. Comparing equal lengths of 3/4" sch 40 and 1" class 200, the sch 40 is more than 40% heavier, which is robbing it of a lot of buoyancy.

Do you intend to have the floats permanently affixed to the tether? Or to attach them as the tether is deployed? Have you settled on your tether yet? If we knew its diameter and its weight per foot, it'd be pretty simple to determine what spacing any particular float requires. Or at least have an informed starting point for testing.

[PaulC]

Well that is some interesting info that you passed on. I was going to attach them to the tether using zip ties, and as for the tether I am beginning to think that I might change my tether from cat 5e to something like that has twice the wires and hopefully not shielded. Yes it will add bulk, but at the same rate I think that having the extra wires for sensors and etc will out weigh the weight so to speak. Although, I haven't made a final decision yet.

[PaulC]

Hey Pilikia how did it work with the thinner walled pvc?

[Pilikia]

I didn't get to it. I've come down with a doozy of a cold. Feeling way too cranky to do anything productive. In one lucid moment, I had the thought that the 1" is really too big. I'd rather try it with 3/4" Class 200 PVC. Next trip to town I'll get some.

In another lucid moment I had the thought I'd rather at least try to make a neutral buoyancy tether without external floats. It seems to me these attached floats are going to make a mess of the tether spool. And the idea of attaching and unattaching them with each deployment seems a colossal pain in the butt. Might even require having an extra hand onboard, which is out of the question for me.

So, this means I have to settle on a configuration for my tether too. Maybe someone can help me with a question I'm confused about. My ROV will have 2 cameras: one sends surveillance quality video topside for use by the operator; the other is an HD video camcorder, writing to its own internal memory card. My question is this: Do I need a coax video cable to send the first camera's images topside? Or can I use some of the wires in a Cat 5e cable for this job?

I'd appreciate anyone's insight and experience with this question.

[PaulC]

Pilikia,
When I built my first ROV I just used the cable that came with the camera and piggy backed it along side the tether, but on my new ROV I am going to take the four wires from the camera and splice them into cat 5e or into a serial cable so that I only have one or two cables going to the surface. I am leaning towards the serial cable because I will have extra wires left over for sensors.