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Release mechanism


#1

Dear all,
I am working on a small photographic project, for now all mechanical at ca. 400 m, but thinking about a way to release a weight electronically (raspberry), ca. 3 kg and maybe expanding to 1000m depth.
How could the release be done? The use of a M100 thruster engine pulling out a release pin comes to my mind, though that sounds complex to me (gear needed?!). Any experience e.g. with magnetic release or other solutions? Suggestions, also for hardware are very welcome!
Many thanks and best regards
Georg


(Dietmar Pichler) #2

Hi,

Did you think about using the Newton Gripper and adopt it to your needs?

„The Newton Gripper is a sealed, single function manipulator which can operate at depths of up to 300 meters.“

Didi


#3

Dear Dietmar,
thanks for the suggestion. Indeed the Newton gripper mechanism type could be an option (is there a step engine inside?). But it is rated at 300 m, and we are now at 400 m and want to go down down down…(1000 m).
I assume that a “mechanical” through-hull connection will be difficult, therefore thinking about a motor or magnet.
Best regards
Georg


(Jacob) #4

My favorite mechanism I have seen so far is called a ‘burn wire’. You have two electrical screw terminals on the outside of the enclosure, and put a piece of nickel-chromium (nichrome) wire between them. Apply power, and it gets red hot. Hot enough to melt a piece of fishing line held in tension against the wire, or apply a bit more power and you can just melt the wire itself!

I had been thinking about this for a long time with magnetic/servo releases etc. When I saw this technique I was amazed; It’s so simple and effective.


#5

Dear Jacob,
thanks a lot, that is a great idea! I had seen before “accelerated corrosion”, but that works only in saltwater. Will try the burn-wire and orientate myself on styrofoam cutters, they use ca. 3A at 12 V, I might have some of that special wire around… Hope the method is not too heavy on the batteries and that I don’t electrocute any fish…
Will keep you posted…
Many thanks and best regards
Georg


#6

Dear Jacob,
I have an additional question: Typically a cable would run from one enclosure penetrator to another, so the outer cable insulation keeps all dry. Now I would have two, rather thick, cables, running through a penetrator and then finishing in two cable clamps (to which the Ni-Cr wire is connected), so the cables are “open” at the end.
I hope I could explain what I meant. Is there a risk that water would seep through the cable inside and is there something that could be done against that? Talking about 100 bar.
Many thanks and best regards
Georg


(Daniel Heideman) #7

@deeplake That is certainly a problem. We have seen water come out of the inside of a stranded wire (inside the insulation) like a jet when testing cables at 100 bar.

You will probably need to use solid core wire potted directly into a penetrator to have any chance at surviving that deep. This includes stripping away part of the insulation so you can get epoxy onto the copper directly.


#8

Dear Daniel,
many thanks for that! Will it be ok to have the wires in one penetrator (less holes in the housing), or would you rather recommend two spearate penetrators for easier potting ? Could it be good to make some scratches in the copper wire so it does not slide? Is there any info about the depth rating of the penetrators? I assume 1000 m are ok, as the 100 bar pressure sensor seems to be mounted in one.
Best regards
Georg