Author Topic: SpaceX 'Octagrabber' (Rocket Grabbing Robot) - Updates and Discussion  (Read 328019 times)

Offline Lar

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I posted my quip to the party thread... don't make the mods crabby by getting TOO attached to your standup jokes.
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline ChrisC

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FYI, this morning the Roomba / Octagrabber / Octacrab has been seen to have been deployed for the first time.  See Canaveral return thread starting here:

http://forum.nasaspaceflight.com/index.php?topic=43222.msg1696595#msg1696595
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Offline Req

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Crossposting from the return coverage thread - this thread really should be in the "SpaceX Reusable Rockets Section."

Late edit - Pics from https://twitter.com/Mike_Seeley/status/880420558386733058

Notice that the octagrabber's "arm" that goes under the most crushed leg junction isn't deployed.  I wonder if the nominal plan is to actually correct the lean, but in this case one leg was crushed so far that they couldn't deploy that arm.

In somewhat recent pictures, one of the arms wasn't deployed and looked as if it was missing hardware(which one person disputed).  Maybe that arm just isn't ready(maybe because they want it to handle an umbilical for those cables under the ladders which were obviously installed by crew this time) and the most-crushed alignment is a coincidence.

I also remember somebody saying that the octagrabber wasn't ready to be used on this landing, maybe the arm is what wasn't ready but they decided to use it anyway.

During Alicia's periscope, a SpaceX employee verbally referred to the roomba as an octagrabber, which is now the second time that I have seen a SpaceX employee use the term.
« Last Edit: 06/30/2017 01:21 am by Req »

Offline matthewkantar

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Notice that the octagrabber's "arm" that goes under the most crushed leg junction isn't deployed.  I wonder if the nominal plan is to actually correct the lean, but in this case one leg was crushed so far that they couldn't deploy that arm.

The grabber you are speaking of would be further around the rocket to the right in the picture. That bundle of plumbing or whatever is between the two attach points of one leg, the stage is grabbed between adjacent legs. The grabber in question may actually be grabbing.

Matthew

Offline Req

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Notice that the octagrabber's "arm" that goes under the most crushed leg junction isn't deployed.  I wonder if the nominal plan is to actually correct the lean, but in this case one leg was crushed so far that they couldn't deploy that arm.

The grabber you are speaking of would be further around the rocket to the right in the picture. That bundle of plumbing or whatever is between the two attach points of one leg, the stage is grabbed between adjacent legs. The grabber in question may actually be grabbing.

Matthew
« Last Edit: 06/29/2017 07:25 pm by Req »

Offline Lar

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Moving a bunch of posts to the party thread.

We're not actually in grammar school. It just seems like it.

"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Jim

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Those pics confirm that the octagrabber is holding the stage and not pulling down against the leg as some have wrongly stated

Offline GWH

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Those pics confirm that the octagrabber is holding the stage and not pulling down against the leg as some have wrongly stated
Looks like the engines are just fine and landing was within crush core margin.

Offline Chris Bergin

Remember to accredit pics even if you copy from a thread where they are accredited. Edit them in if you missed them.
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Offline CameronD

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Whilst marvelling at this pic in the Return thread showing a landed booster from sea level, it occurred to me that a deployed 'Octograbber' will most likely come off second best if the booster (being the tallest object for miles around) got hit by lightning on the tow back to shore. ..but maybe that's a better outcome than losing structural rigidity in the legs and potentially losing the stage overboard?



EDIT:  https://twitter.com/Mike_Seeley/status/880407593042182144
« Last Edit: 06/30/2017 12:09 am by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Lar

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Um?

Carping got grabbed and crushed.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline woods170

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Those pics confirm that the octagrabber is holding the stage and not pulling down against the leg as some have wrongly stated
Correct. In the original set-up (pre-Octograbber) hight-adjustable steel posts were placed underneath the stage to support it. Additionally chains were tightened between the deck and the stage to pull the stage against the posts. But once firmly secured to the posts the legs no longer carried all the weight of the stage; the load was shared between the posts (majority) and the legs (minority).

Octograbber basiscally automates the posts. It rolls in underneath the landed stage, grabs the stage and pushes against it until Octograbber supports most of the weight of the stage. Octograbber also holds the stage firmly in place by attaching itself to the deck.

Offline Semmel

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Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

Offline Jcc

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Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.

Offline xanmarus

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I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.
It's have tracks not wheels.

Offline rsdavis9

Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.

Also it was suggested that the shear mass of the roomba provides the support that attachment would.
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Offline fake_name

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Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.

Speculation, magnets.

Offline rsdavis9


Speculation, magnets.

I suggested that a long while ago.
Have we seen electric cables going to the roomba?
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Offline Semmel

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Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.

Speculation, magnets.

If speculation is all we have and unless woods170 has direct information, we dont know if or how the Octograbber is attaching it self to the ground. Just holding the stage by its mass is a viable concept but not attaching. So lets not get ahead of our self and stay true to the facts.

Offline fake_name

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Octograbber also holds the stage firmly in place by attaching itself to the deck.

Maybe I missed it, but I have seen no evidence of that.

I assume it is "attached" by friction, by lowering the chassis until it contacts the deck, instead of being supported by wheels. The only evidence appears to be the low profile of the octagrabber, but we can't see the actual contact with the deck.

Speculation, magnets.

If speculation is all we have and unless woods170 has direct information, we dont know if or how the Octograbber is attaching it self to the ground. Just holding the stage by its mass is a viable concept but not attaching. So lets not get ahead of our self and stay true to the facts.

I think it's quite easy to rule out friction alone, \mu = F_r/F_n

If the barge is moving up and down in the swell, F_n is changing, it will increase as the barge rises (accelerates up) and then decrease as the barge falls (accelerates down).

Wouldn't take much more to find the coefficient of steel on steel or steel on painted steel, work out what the swell size is, figure out the reduction in the normal force then find the force that would overcome friction in that situation.

My gut feel, friction is no where near enough, not with the surface area of the roomba, the contact patch is only the underside of the outside steel beams? If there are any fasteners or such sticking out on the bottom, would make it worse.

The other options off hand are:

- some type of fastener (drill and tap a hole in the deck and drop a bolt in? or a rivet?)
- weld some lugs to the deck then chain block the roomba to the lugs (what happened previously, I saw some welded lugs in early barge photos)
- ?

Maybe the roomba is full of lead ballast?

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