Electronics tube depth test VI


This post WILL contain magic!* As this is my third attempt to write this (previous attempts were thwarted, no doubt by ancient powers, wishing to protect secrets of the arcane from the uninitiated. Or a power outage and strange webpage glitch that deleted all my text when I clicked save as a draft to prevent that very thing!)

On no few (or greater) than 3 occasions this week, I felt the instinctive need for proof!

It is possible that one of those occasions was due to over excitement and/or low expectation. 1 & 1/2 of them however were pure magic!*

Also there will be pictures.

This is the 'rig. It now has 2 shelves. and rope. I looked up knots online, and chose a round turn and 2 half hitches with which to fasten the ropes. I'm sure it will be fine.

If I am wrong and I should use different knots, let me know!

I am still setting up the 'rig' but you get the idea.

This is a light module it will light both the test area and below the 'rig'

See the spool of cable on the right? Note how loose it is?

Let me save you from spool of cable hell by saying DON'T LET YOUR CABLE GET LOOSE. Holy Jumpin'. I am so so oh so lucky that I decided to re-do it to make sure it fit on the spool better. I didn't know until I was part way through (quite early on) what trouble a loose would be. It started to unravel and fall off the sides. At one point I had a loop, that my lead was passing through, and I had to feed the new spool through said loop over and over until I reached the point that the loop came off the spool.

I have no pictures. It didn't occur to me that, pictures of utter failure, could be useful, until I managed to slip out of the jam. :)

Lesson learned. Here is the setup I used to wind the cable onto the spool. The orange wheel is for measuring distance as you walk. I am using it here to measure the length of the wire, but I bought it to use during the test, to see how much line has played out, and judge depth. There is some error to work out.

First the center of the wire is the distance that needs to be measured and it is an 1/8th of an inch from the edge of the wheel. That changes the diameter and circumference. The wheel normally measures 1 foot per turn, but the wire is spread further and each tick on the meter is actually about 12.27".

Second the rope will stretch some. I don't know how much, I will try to find out. :)

I added this adjustment to help keep tension on the wire and keep it from derailing. I hot glued disks to the outside of the wheel to keep the rope/wire/cable on.

Don't worry, magic* is coming.

Okay, so this is the first incident of 'proof need feeling'. I was trying to determine what length of cable I could get a signal across. I tried at the full 305m (1000') but no signal. I soldered quick connects to make testing faster, anticipating many cuts until getting a signal. So I chopped off 10m. Tested. Low and behold a strong signal and what i will call 295m. I did not expect this but perhaps I was just pessimistic.

The pictures above are:

Left: Set up, Middle: OpenROV connection, Right: Raspberry pi Camera connection.

What none of these pictures is showing you, is proof. And that is sad because that is why I took them. lol. The one just above was intended to show all the connected wires. Really was just crazy happy.


This was supposed to be in the post just above the first video. I tried to edit it but noo dice.

So here it is:

Okay so here is the magic!* The gist of it is that the homeplug adapter was connecting to the rov with out wires attached. I'm not exactly sure why/how. I expect that it needs to be a pretty strong signal off a short tether wire. But the signal was strong and the streaming video coming off the rov was as high frame rate as I have seen. The video is all over the place as I try to find out wtf.

If this worked at the end of the tether it could be useful. We could attach the tether with magnets with the adapter inside the acrylic and the wires outside. I tested it and I was able to put acrylic endcap pieces between the wires and the adapter without breaking the signal.


Nice work. I would argue against using a float as a TMS but there may be a "magic" combination of tether drag and buoyancy that may not not adversely affect ROV control. Looking forward to the results!


I fear you are correct about the float. I hope it works well enough that I can at least poke around a bit at the bottom. It’s the only idea I have for remote TMS, but if there are other ideas out there please don’t keep them a secret! :smiley:


Motorized spool. have it tied into the PWM for the forward thrusters, i.e. your forward vector control signal so it would spool out at the same or slightly faster than your forward drive, but have it independently retract at a slower rate for safety. also not sure about the tethers buoyancy, best to have it as neutral as possible via ballast attached along the line. syntactic foam bits or fishing float bits (you'd have to hack them up to get the right buoyancy, if needed.


That does sound ideal. I don’t think I can manage it by Sunday, :slight_smile: but that would be a great system, and I do plan to need one in the future. Would you put the spool on the rov? Or on the rig?


Rig, definitely. What happens is that as you increase depth, the thether drag actual impacts an ROV the most. You have to pull and deal with x meters of tether. This is the most limiting factor on ROVs. By having the rig deal with the tether, you remove the tether drag that builds as you dive from the surface. TMS systems like this are used for just this reason. Smaller ROVs can dive deeper and not be hindered by the miles of tether above them. just concerned with pulling around the tether that trails to the rig. Having a rig for an OpenROV really opens the doors for these guys to dive deeper...that is once an oil filled or stronger housing is made for the innards and motors.

But in any event, a depth testing rig is great. A deployment rig with a motorized TMS for the ROV is definitely on the wish list.


I would argue against using a float as a TMS but there may be a "magic" combination of tether drag and buoyancy that may not not adversely affect ROV control. Looking forward to the results!

Good point. I'll be interested to see how this works as well.

Another option, if all you are trying to do is minimize tether drag at depth, is to fix a weight on the tether, say 10-20 meters from the ROV and then lower to the desired depth. The weight will help counter the current and only the remaining 10-20 meters will be effected. That is assuming you are using a tether capable of handling the additional weight. Have used diving weights on tethers with VideoRays (and the like) to accomplish this in the past.