Homebuilt ROVs Forum

Has anyone considered using pool cleaner cable as a tether? They are a bright blue colour and covered with UV resistant waterproof foam for buoyancy. The normal configuration is 2x0.75mm2, which could be enough for both data and power if you use the powerline/HomePlug LAN hack. I haven't found a source that sells this cable by the metre, only 3000m reels, and as spare parts for pool cleaning machines they are pretty expensive ($150 for 20m) - but maybe someone knows someone who has a pool cleaning business?

Ideally, you'd want the tether to be neutrally buoyant. If it is too positively buoyant, the ROV will get to a point where it's vertical thrusters can't overcome the buoyant force of the tether and won't be able to dive any further.

jpWA wrote:If it is too positively buoyant, the ROV will get to a point where it's vertical thrusters can't overcome the buoyant force of the tether

Good point! A case of "too much of a good thing" I guess Since I posted this I have come up with an alternative option which I think will work much better, and which will allow me to adjust the buoyancy of the cable to match the weight of its members fairly closely:

It is possible to buy foam tubing in a variety of materials, EPDM, silicone and neoprene being the most interesting ones (due to their ability to handle UV light and salt water). There are many manufacturers of this type of product and there's a plethora of dimensions (diameter and wall thickness) as well as a choice of colours (high-visibility being desirable). I am currently trying to get some samples from a couple of manufacturers so I can do some testing - but it's still early days for me, I don't even know what cable area I will be needing, the actual cable to use or the strength member (monofilament or 316SS) - all of which depends on other parameters (power draw, feed voltage, total ROV mass). Then there is the question of how you pull 50-75-100m of cable through a tube - though I suppose it could be slit open and either glued back together or placed inside a nylon mesh "sock" - tedious work in either case I am sure!

Great find Lomax, the pool cleaner wire didn't excite me too much due to it's price and only having two wires.

The tubing however looks like it could be a winner! I think if you could get it in 20m lengths threading it on to a cable would be possible if laid out in a straight line, first you would pull a string through it with vacuum cleaner then pull your cable through with that, it would take a few helpers though.

The only down side may be compression of the foam at depth and the resultant loss of floatation.

kenl wrote:the pool cleaner wire didn't excite me too much due to it's price and only having two wires

Yeah, same here, which is why I kept looking for alternatives. The pool cleaner cable is 1) too expensive 2) too weak 3) too thick 4) too buoyant. While I thought it was interesting at first I now consider it a non-starter.

I never liked the idea of strapping floats to the cable either. But there is just no way around it; you have to have a cable (unless you go fibre optic), it has to have some buoyancy, and ideally be strong enough to retrieve the ROV with in case of a malfunction. Something must provide that buoyancy! Once I accepted that I was only a quick web-search away from an abundance of options!

kenl wrote:I think if you could get it in 20m lengths threading it on to a cable would be possible if laid out in a straight line, first you would pull a string through it with vacuum cleaner then pull your cable through with that

I have a slightly different idea: I think if you lubricate the cable with something (ummm... how about silicone!) and attach a firm "needle" object to one end, say a foot or so of some thin metal rod with a rounded tip, I reckon you can thread it through with a little effort. Since the foam tube will have some elasticity it will open up when you push it over the "needle" and you can probably push waves of expanded tubing along the cable. Of course this means it will take longer and longer time as you progress (since you'll have to push each "wave" all the way to the end of an ever longer piece of tube) but with patience and a bit of elbow grease I think it could be done! How much elbow grease depends on how tightly the cable fits - by leaving a little extra room the job should be easier.

kenl wrote:it would take a few helpers though.

Help is always good - unfortunately also in very short supply here! If it's going to be done I'll have to do it myself.

kenl wrote:The only down side may be compression of the foam at depth and the resultant loss of floatation.

Yep, but I think we'll just have to live with that. In fact it may even be a good thing as the cable will become increasingly buoyant as it reaches towards the surface, it's possible this will keep it at a sloping angle which should help avoid entanglement. Maybe this effect should be taken into account, by dimensioning the foam tube so that the cable is ever so slightly positively buoyant at surface pressure?

I'm always open to suggestions though, so if anyone can think of an alternative...

Good find Lomax will be interesting to see your results! If you find out the density it could be worked how much buoyancy it would give.