ROV for Dive Team

[81D1]

Hello all,
I'm starting a winter project and want to build an ROV for our Dive Rescue/Recovery Team. I have plenty of parts from other projects that I hope you will guide me in using!
1) Since I bought a GoPro I have no need for my old and bulky video housing. She's solid and watertight.
2) Years ago I built a DPV with two trolling motors that I will use again. The unit worked (had trouble with off/on switches though which I'll ask about later!) but was made from a wooden hull that eventually leaked too much to bother fixing.
3) An underwater comm unit tether for a full face mask This I think I can use if I have onboard batteries. Maybe need to add another wire or 2? It is a floating rope with one phone wire attached.
4) There are lots of other fittings, clamps, boxes, arms etc. that I have already as well.
Any suggestions will be greatly appreciated. I realize this is already going to be big and heavy but that's OK, I'd rather overkill a bit. If I can prove the concept and show how valuable of a tool this can be for us I may be able to build or buy a better one in the future.
Questions? Comments?

Thanks!
Harrison

[81D1]

OK so I've made a few decisions that I hope will move this along. I made the skids over the weekend.
Next I'll make a front piece that will hold a scuba depth gauge and compass. I'm only using the old video camera housing with bilge pumps, not going so big as to use trolling motors. I have one bilge pump already that will be for vertical thrust and am going to buy a pair for forward/reverse/turning. The housing can handle at least one of my 12v, 7ah batteries and the camera.
Obviously the floats are only there for example. I most likely will not need that much buoyancy. I will get a dome for the camera side and can extend the back if necessary. Most likely I'll use dive lights for now and they won't need to be wired in (maybe in the future).
Thoughts?

[rossrov]

Looks like you're off to a good start with that box of goodies! Just wondering why add the complexity of adding a dome when what you have already works?
3 thrusters is what I used and found limited things. Next ROV will have more. Making another 2 is no real extra work once you're set up and worth doing IMO

Ross

[81D1]

Thanks Ross! So first you'd go with two vertical thrusters? I thought about the dome too. I want to get it eventually (may need room to upgrade things, and they just look SO cool!) but won't need it to get this going so you are right about that.
Can I get enough from two phone cables to control the motors if the battery is on board, or will I need a Cat5?
Thanks in advance!

[a_shorething]

Thanks Ross! So first you'd go with two vertical thrusters? I thought about the dome too. I want to get it eventually (may need room to upgrade things, and they just look SO cool!) but won't need it to get this going so you are right about that.
Can I get enough from two phone cables to control the motors if the battery is on board, or will I need a Cat5?
Thanks in advance!

So for the control thing: You have quite a few options but it depends on what you're looking to do.

You need to get video up topside and you need to control the motors.

The guys at OpenROV have their system set up to use a single twisted pair of wires to the ROV for everything and if you're clever you can do it that way. The systems I've read about include:


Two wire: (like OpenROV) all communications go between a laptop up top with a board connected to it, then another board on the ROV to recieve/control things.

Two sets of wires: one pair for video and one pair to control everything else

Cat-5: Technically Ethernet communication only uses 2 pair out of the 4 pair that are in the wire, but the way the plugs are set up you have to hack it or use a splitter at one end and a joiner at the other and you also need a switch to talk to two separate devices/IPs. Alternately you can just use the Cat-5 for the conductors/twisted pairs available (4 pairs=8 wires total) and figure out the best way to use them.

Multiple wires bundled together: This is for people who power their ROVs from the surface so a pair might be for power (thick gauge like 18- 16 AWG or thicker to offset resistance due to wire length) and another wire/set of wires for comm.

Most of this is dependent on how you plan to control it and monitor it. If you're using a laptop you have one set of options, if you're wiring up a remote control and monitor you can use switches and have to figure out the logic/wiring to get it to have more finesse than off/full power for each motor.

Everything (in my opinion) depends on the UI you choose. Once you know how you want to control it and view the video that will start you on the path to how you'll have to handle the tether and control setup.

edicated video and separate control

[81D1]

OK I know that I want batteries onboard and a simple switch box (no laptop) control. I will get some Cat-5 and with the phone wire I should have more than enough wires to get the job done.
Thanks!

[rossrov]

Possible disadvantage of a switch-controlled approach, keeping electronics to a minimum, is that you need a conductor for each motor, plus a common. So for 5 motors you need 6 wires. That leaves 2 for the camera assuming cat5 is used. To be able to reverse the motors represents a slight challenge, but easily enough done. Topside you would have two small 12 batteries connected in series. The common wire goes to where the positive and negatives are connected. To send a fwd command you connect that motors wire to positive, and for reverse to negative. In the ROV you have a total of 10 relays, 2 for each motor. The relay coils are connected to the motor control wire in the tether via 2 diodes, so one relay closes for fwd, the other for reverse.
Given the mass/inertia of the typical ROV, simple on/off motor control is quite acceptable I think, provided you have a means of actuating microswitches such as joysticks and some linkages. To have an array of toggle switches will not do. You need to be able to manually "pulse" a motor for a split-second to get fine movements of the ROV.
For an ROV of your layout, yes, 2 vertical. 2 small lateral and one forward/reverse, or possibly 2 wired together for more power or better placement on the ROV layout