Is there build in a weaklink like a shearpin in the gripper in case we end up with a dead BR2 or just that the gripper does not respond to our commands? This is a very common feature build into other SSA.
If not, we can possible have a case where we are attatched to something at depth and not able to get loose from without breaking the claw or damage something else on the gripper. Been testing the NS Gripper several times the last days and really satisfied with it.
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good point @SHS !! you just anticipated a future problem I hope the BR engineers could help us with this.
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Hi Svein,
That’s an interesting comment! I can’t say that we even thought about including a failsafe mechanism for releasing the jaws in this situation. I think that’s a nice feature, even if it only needs to be used in extremely rare occasions.
I’ll bring this up with our team and we’ll consider adding it to a future revision.
-Rusty
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There is several ways to make a weaklink on the gripper as it is made today, but it reqire som matematics…
- Replace the nut that secure the sylinder rod to the gripper with one that burst at a calculated Nm.
- Replace the bolt that attach the two fingers with a weak bolt made in a material that will break at a calculated Nm.
Just some ideas that i have based on what i have seen earlier in the subsea buisness
Hi Svein,
Under what sort of conditions would you want the weak-link to fail? I think there are many situations where you may want to grab something and then pull fairly hard on the tether to retrieve it. In that case you’d want the gripper to be pretty strong.
-Rusty
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I would not plan to recover anything with pulling the tether. I will attach a rope from surface with a hook to the subject i want to recover with the gripper. I love my BR2 and think we should be careful with using it as a winch. The framework is not titanium…
Lets say that you are observing something over a longer period at seabed and you are able to grip to a mooring or something else you cant pull up. You can then extend your divetime significant because you are not using any power to stay down. That was just one example, i. can find many other
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Which other mini ROV’s have weak links in their grippers? I’ve used quite a few and wasn’t aware that any had such a thing.
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You will not be able to see it before you start dismantling the claw. I have not been using grippers on mini rov, only WROV, but still think that it is a smart thing to have.
If it is eletric/hudraulic manip i will guess that they are set ut with a open senter valve. If you switch of or loose el.power it will open automaticly.
I can see where it might be useful in certain situations but could also be a liability in others. “Auto opening” if the ROV looses power might be the safest solution.
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@paul-unterweiser That actually sounds like a really good idea. Have another safety feature in the Vehicle → Safety menu so that when the ROV disarms, not via a the button press, but via one of the already set-up safety functions (loss of GCS control, loss of pilot control, leak detected, etc) the gripper will just automatically open.
@SHS and @luisgamez Would something like that with a safety disarm → gripper release work for you? This would obviously be an option you could enable or disable for the work you were doing.
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I´m pretty sure thats a good solution @kklemens. @SHS has pointed a very particular situation used mostly in the O&G where mooring to a grip or a structure is needed on some tasks however the BR2 is designed for professional jobs and adding this function will take it one step closer to WROVS scope of work on a “miniROV”
Indeed, for WROVs usually there is a loss of jaw lock in the case of power loss. The jaws wont so much open on their own as much as they simply stop being locked closed (power keeping them forced closed) allowing the jaws to part on their own when pulled during a dead sub recovery. However in the event of a dead BR2 you will want the jaws to pull apart when the tether is pulled from the surface and just hope the ROV is not in a bad position, but this comes down to correct mission planning.
Having QGC open the jaws in certain safety scenarios is a great solution.
Being battery powered means its primary problem could be flat battery or ruptured battery. Ideally if the jaws have no power you will want them to be easily pulled apart by hand. Only engineering problem with that is that you need a design which constantly uses power to keep the jaws closed. Not great for battery operated systems.
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