A Canadian Boffin

Here’s the finished hull, with the first version of the claw, but no guts.

Controller

The controller filters the video signal a bit for noise, and takes the stick inputs and sends them down the cable as a serial signal. It also receives instrument readings from the sub, and displays them. Initially, the sub had no instruments, only video. We quickly found that a compass and depth gauge are absolutely essential, so they were installed after the first few trial runs.

Note that the cable is just good quality, four-conductor microphone cable, with a braided metal sleeve. This actually works well as video “coax” surprisingly enough, with three lines remaining for 1 amp of power down the line, and two-way 2400 baud serial.

Note that you can only get about an amp down easily, so the sub mostly relies on an internal 6v, 4.5ah battery. To push more down from the 12v house batteries of the “mother ship” boat would require a heavy-duty DC/DC converter.

Here you can see the sub-end microcontroller board and motor-control board. Straightforward N-channel mosfet H-bridges provide proportional control at up to 25 amps per motor. The sub microcontroller can also carry out an emergency ascent if the cable is severed or control is otherwise lost.

‘Field Trials’

The sub has seen probably only around one or two dozen sessions of use, both based from cruising sailboats or at Ryan’s family cabin. So, it’s just barely out of field testing, three years after the project was started. Fun though. Our friend and fellow beer pirate Russell christened it ‘Rusty’ on the first big outing. It’s apt; the claw fittings are made of several different metals, and the inevitable results drip from it.

Here’s Colin (left) and myself (right) prepping it for a test dive off of a dock.

Cruising at the surface…

Verdict: Control is fairly good to very good, but battery life, less so. If we blast around at full power, it’s only about 10 minutes. Puttering around, about 45 minutes on a battery charge. The motors really needed to be geared down, or optimized for a lower RPM – but that’s one of those early design decisions that’s hard to get around now.

A Life Aquatic

Here are some images of Rusty’s adventures – as you can see, there are some drawbacks to the simplicity of using standard video. Mainly, the difficulty of screen captures!

Post-flood cleaning:

There have been two instances (on the same trip) of total face O-ring seal failure, at about 15m depth, we think due to a slight slope on the rim of the main hull facing. The problem seems to be resolved now, with the help of Owen, a civil engineer by training. A fast recovery by the cable, and thorough flush with fresh water, is all that’s needed to get back into action. The electronics are actually fairly robust.

Normally though, it’s pretty dry. Ironically, the motor stuffing boxes (driveshaft pass throughs) were the biggest worry at the design stage, and yet seem to work perfectly and wear well.

When Sunstars Attack

One one trip, we were sitting on the bottom, wondering how to spend our last few minutes of battery life, when an overly friendly sunstar tenticle eased itself over the viewfinder. And then another…then we found we couldn’t move all that well, especially vertically.

After pulling it up by the cable, we caught the gooey, spongy perp in the act:

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1. i like you´re sub . what kinde of powersorce do you have . do you power it frome the surfase or do you have onboarde power. i´m bilding me my own sub but i have gone fore two pods that i can rotate.
   — jesper    Dec 1, 08:43 AM    #
2. I wish I had the know how to make it work. Great Job!!
   — erd    Dec 3, 06:36 PM    #
3. Hi, I have some questions on your ROV :
   – If I see it right, you measure depth ? How did you do that, what components were used ?
   – Same question for the compass and the “claw”
   
   Do you have any detailed drawings, pictures ?
   
   Many thanks !
   
   Tony
   — Tony    Oct 29, 08:06 AM    #