2.5 Build Questions


Not sure if this is the best place for my questions -- if not please let me know where I should post.

I can't seem to find instructions on a couple things

1) how to wire up the lasers -- I can figure out the alignment, but don't know where to plug them in

2) how to wire up the depth/pressure sensor

3) how to fit the USB regulator into the case without breaking off the adaptor piece from the regulator board.

I have made a bunch of mistakes along the way (and still have a ways to go), mostly from not reading carefully enough. Even so, when I have the ROV complete and working, I will make a list of mistakes I made since that might help the next guy. But where should I post that?




Can't help you on the lasers.

Depth sensor assembly:


If you refer to the main wiring diagram for the DB-25 plug it lists the 4 wires for the depth sensor at the top left. The names match on the sensor board so you know where to solder them on.


After the depth sensor is all wired in you have to enable it in the software - found here:


There is no need to SSH into the device, in the newest software you can use: (cloud 9) to log into a web interface and edit the software files. Make sure you don't log into the cockpit before trying to load cloud9 or it wont load.

I found if you just use hot glue to seal the other unused wires it doesn't seal. Had a small through the wire at depths of 30 - 40 feet. Make sure to use the sealing heat shrink tube to seal those wires up.

Not sure what usb regulator you're referring to?




Thank your for the help. I know recall having seen the depth sensor instructions that you linked, but I can't imagine how I got there. I wonder what else I am missing. Time for more exploring!

The USB Reg board is shown in step 77 -- it gets connected by 3 wires to the second homeplug adapter, and both of those get fit into the topside adapter box.

Thanks, Rick


Duh, sorry. It took me a while to figure out the topside adapter and how exactly it went together. If you get it right, the USB reg should slide in with just enough room to fit very tight. Getting all of the stuff in that box is a trick for sure :)

They actually haven't had time to post the instructions for enabling the depth sensor. Having bought one of the first V2.5 kits I was working through it as they were still making the assembly instructions. This is still a work in progress for sure. Dig around in the main page's blog posts and you'll find some very helpful info. That is where I found the steps for enabling the sensor.

FYI, Sealing the electronics tube is a task! I would not recommend using Teflon tape. If you cut little strips out of balloons they fit nicely under the o-rings and make good spacers for the main tube and battery tubes.


I see what you mean about sealing the electronics tube being difficult.

I could sure use some pointers.

Why latex balloons, instead of rubber (or whatever)? I haven't found any locally that are labeled as latex.

What pressure (vacuum) should be held, for how long, with how much loss? I am at the pressure testing stage. 11" bleeds down to 10" in about a minute. So I put one end (in this case the non-wire end, which looks like it has a great seal) in a bowl of water and sure enough about a teaspoon full of water leaked in over the course of about 60 seconds. I intend to put some tape over the syringe hole (on the inside) so hopefully I can determine if that is the source of entry of the water. If that is not the source, I will try re-doing the teflon, but I think I did a really good job so I am not optimistic about any improvement there. So, I will now try the latex balloon idea. (I would have sooner, but can't find latex balloons locally.)

If water is is coming through the syringe hole, I will be tempted to epoxy the whole thing, since I can't understand why it is necessary to pressure relief valves on both sides. If I am missing something someone please let me know before I mess this up. By that token, I don't understand why one of the endcaps isn't epoxied to the tube. Why does the non-wire end cap have to be removable?

thanks for any tips -- Rick


Hey Rick,

I didn't use latex balloons. Just your average walmart balloon pack works. I cut strips out of the neck of the balloon to get rings for the battery caps, and strips out of the fatter part to get rings for the end caps.

The little plungers are to equalize the pressure in the tube before diving. This helps seal the o-rings better as you get deeper.

I had leakage from two areas.

1. The end caps were leaking because the O rings were not tight enough. I had to put 3 spacer rings under each one! It should be somewhat difficult to put the caps in when the o-rings are tight enough. You can see how much mine are pressed against the tube in the attache photos. I also *carefully* sanded a little ramp on the inside of the ends of the e-tube to help the o-rings pop in. You really don't want to scratch the surface where they sit.

2. The 6 aux wires (4 for the depth sensor) need to be sealed up individually with the heat shrink tube that has glue in it. I had just put hot glue on the ends of them and it was leaking all the way down the wires and into the e-tube.

Mine is tight. I had it down 5 - 6 meters yesterday for over 20 minutes and it came up perfectly dry, battery tubes and e-tube. The balloon spacers are the only way to go. I highly doubt your pressure plugs are leaking.

The spacers should be cut just wide enough to fit in the groove under the o-rings.

Check out the pics.

928-cutting.jpg (560 KB) 929-freewiressealed.jpg (527 KB) 930-oringset.jpg (548 KB)


Right, you could easily glue 1 end cap on for good and seal its pressure release valve. I guess the only drawback would be if you broke the e-tube or scratched it bad and needed another one. Would have to build a new end cap as well. It is possible to get them both sealed up good :)



I struck out with the teflon tape and have tried the balloon strips, but am running into a couple problems. First, I can't seem to get the balloon strip in position to lay flat. Sounds like it should be easy, as I can envision laying it down flat, but invariably it gets off center, twisted, or otherwise imperfect. I will try again (and again ...), but I am wondering if you discovered any secret process? Am I correct that the balloon strip must lay down flat in order not to allow water to leak underneath?

Your o-ring is way tighter than mine. When I try to make mine tighter than it is, my o-ring gets pinched and the endcap won't go on properly. Sounds like I need a better ramp. I will try that, too. (Thanks for the tip.)

My leak problem may be caused by a lack of concentricity in my end-cap plates, which resulted from the syringe holes being too large to provide a tight fit with the syringe pieces. I did my best to keep them concentric, but it is enough out that the o-ring protrudes unevenly above the outer plate. I am thinking that may make a good seal difficult or even impossible. Anyone else have that problem?

If I have to rebuild endcaps, maybe I should wait for version 2.6? Will that be backward compatible?

Any advice would be greatly appreciated. I am very anxious to splash my ROV -- this is the last step for me. -Rick


The balloon strips get twisted. Use grease and a small flat head screw driver to flatten them out. Use a generous amount of grease to get the caps to pop in. This takes some finessing.