Fail Safe

#1

I was looking at the tether discussion in the blog area and noticed that the fail safe issue came up. Personally, I would be pretty disappointed if I lost an ROV worth several hundred dollars at the bottom of a lake or something. I'd like to know what sort of ideas other people have at this point.

I was thinking a small high pressure air tank or CO2 tank could be used (paintball gun tank?). When a communication failure was detected, a valve could open and release most of the air in the tank. The loss of weight of the air while the tank maintained it's volume might create enough buoyancy to lift the ROV. The expelled air could also be captured and used for lift, but that might make a more complicated system.

What other solutions are out there?

#2

Much easier way! Put Rc Fail Safe for the depth thruster (Something like this). Set it up so, when signal lost it will power the thruster and ROV will rise to the top.

#3

It dosent matter, ROV will rise to the top away from you anyways (it wont come back to you, for that you need gps and other electronics), the fail safe wont trigger forward pushing thrusters only the lift thruster.

#4

I think it is a good idea to power the depth thruster in the event of signal loss. Better to look on the surface than in depth if ROV is lost. Since the ROV has an onboard computer, this can be programmed ( I assume, I'm not a programming expert) into the software, use a watchdog on communication and if no signal or commands is received within say 5 or 10 minutes then the depth thruster is given say 25-50% upward thrust. Combine this with blinking the onboard LED's on an off, this will offer better chance of spotting the ROV, especially in low light conditions. You may call this an emergency mode, with predefined logic on what action the onboard computer should take.

This can also be used for exceeding maximum depth, which can also be programmed if you have the depth module installed. In the event of exceeding maximum depth the depth thruster kicks in.

The easiest way meanwhile I guess, is to have the ROV slightly positive buoyant, so that in the event of loss of tether, it will eventually float up.

#5

Had a few ideas, that I’m not sure how many would be feasible via actuation or in advent of power loss:

1). “Dust Off”(http://en.m.wikipedia.org/wiki/1,1-Difluoroethane)/solenoid actuated lift bag
2). Calcium carbide (http://en.m.wikipedia.org/wiki/Calcium_carbide) lift bag. Either with solenoid valve or an idea I thought of called a “sugar valve”. Sugar valve would be a physical barrier that would melt over time with exposure to water (think candy or sugar glass). Would take testing and constant replacement (per mission), but could be made simply and cheaply. I was inspired by either something I read about fishing or making cheap oceanographic equipment. Original idea involved using a Lifesaver candy along a fish line to either convey and drop a payload, or to release a towline if bitten by big fish (used as trigger).
3). Alka Seltzer tablet lift bag: similar to the above, but would use easier to obtain Alka Seltzer tablets inside balloons or lift bags.
4). As a tangent: a failsafe trigger as pre made from Mike’s Sub Works (USA).http://www.mikessubworks.com/page1.html

Have a few other ideas that I will add when I am off my phone!

#6

New here and to the overall ROV community as well. I'm looking into getting started with this project and concerned about the same issue.

I was thinking that since its tethered anyway, loosely wrapping the tether in an 50-80 lbs test braided fishing line would be a simple solution for a fail safe. If the braided line is a little shorter than the wire communication tether it could take the stress of the retrieve.

Amazon - braided fishing line 80lbs test


Disclaimer- I'm not that far into the project to really be offering advise so please shoot this down if it's not viable.

#7

Using emergency assent sounds cool. Be sure to work around the controller board power on/off. If somehow the tether does get cut, the default behavior of the board will be to shut down all power on the ROV. There is a jumper that I think you can bridge that will override that behavior but you will have to power on and off by physically disconnecting batteries or some other technique.

Good luck!

-Brian

#8

Hi

For a safe, thin, strong and light security line, I recomend using Spectra-2000 thread. It can be bought in brigth yellow or orange-safety colours.

Regards

#9

I brainstormed for a while about how to create a cable-less fail-safe return to surface. in the end i decided to use an air soft co2 grenade for a co2 release mechanism to release co2 for a 12 gram cartridge into a milk jug (could be replaced with something of a similar size that looks better) with holes in the bottom of the jug ( part facing down depending on the orientation) dosnt have to be the bottom of the jug to prevent the milk jug from exploding because of pressure, this also allows water that the jug gets filled with before submerging. for a release mechanism i am using an electro-magnet so if power is lost (which it will be in a failure situation eventually). once power is lost the electro-magnet will release allowing the spring loaded grenade to puncture the co2 cartridge filling the milkjug with enough co2 to lift the rov to the surface