Author Topic: SpaceX 'Octagrabber' (Rocket Grabbing Robot) - Updates and Discussion  (Read 328075 times)

Offline JamesH65

  • Full Member
  • ****
  • Posts: 1559
  • Liked: 1739
  • Likes Given: 10
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?

It won't get 'lighter' as the barge drops, because they are both falling under the same force of gravity. It will get 'heavier' when starting upwards as the barge will be pushing against it as it accelerates up due to wave action. There will also be a side to side force from rocking, the torque on the base would be considerable, but that's not a grip problem, that's a hold down problem.

To me, simple rubber on the underside would increase fraction dramatically, but TBH, that thing must weigh at least 10000kg and won't be any easy thing to move even when holding the stage, even with just steel on steel.

I'd like to apologise for this post, having re-read it, it's somewhat bollocks - not sure what I was thinking. The roomba and barge are in freefall as the barge drops off a wave, so the friction does drop off dramatically.

Offline fake_name

  • Member
  • Posts: 12
  • Liked: 7
  • Likes Given: 1
I got boared and found a pic the shows the lugs welded to the deck.

They are using an L bracket design by the looks,

I found the image here: https://i.stack.imgur.com/RNi81.jpg via google.

Offline vanoord

  • Full Member
  • ****
  • Posts: 693
  • Liked: 450
  • Likes Given: 106
To me, simple rubber on the underside would increase fraction dramatically, but TBH, that thing must weigh at least 10000kg and won't be any easy thing to move even when holding the stage, even with just steel on steel.

Steel on steel, particularly when wet is a bit slippy.

The simplest answer is to leave the tracks in contact with the deck - that would probably be enough to prevent it moving.

The alternative would be dense rubber pads on the underside of the octagrabber, but all they would do is act as a substitute for the tracks if the tracks were lifted, so why bother lifting the tracks?

The slight issue about rubber pads on the underside of the octagrabber would be that if the tracks were partially retracted and it tries to move, the pads would be ripped off.

Similarly, the fitting of pads would increase the maximum height of the octagrabber - for example, 1" thick pads would increase the height accordingly, which could create an issue trying to get under a stage with fully-collapsed crush cans.

Simplest answer is to rely on the tracks for friction, which has the additional benefit of keeping the overall height lower.
« Last Edit: 07/04/2017 11:38 am by vanoord »

Offline Jcc

  • Full Member
  • ****
  • Posts: 1196
  • Liked: 404
  • Likes Given: 203
To me, simple rubber on the underside would increase fraction dramatically, but TBH, that thing must weigh at least 10000kg and won't be any easy thing to move even when holding the stage, even with just steel on steel.

Steel on steel, particularly when wet is a bit slippy.

The simplest answer is to leave the tracks in contact with the deck - that would probably be enough to prevent it moving.

The alternative would be dense rubber pads on the underside of the octagrabber, but all they would do is act as a substitute for the tracks if the tracks were lifted, so why bother lifting the tracks?

The slight issue about rubber pads on the underside of the octagrabber would be that if the tracks were partially retracted and it tries to move, the pads would be ripped off.

Similarly, the fitting of pads would increase the maximum height of the octagrabber - for example, 1" thick pads would increase the height accordingly, which could create an issue trying to get under a stage with fully-collapsed crush cans.

Simplest answer is to rely on the tracks for friction, which has the additional benefit of keeping the overall height lower.

My thinking is they rely on gravity and friction, but they do need to bring the frame into contact with the deck, because the tracks alone are not stable enough, but in so doing some of the weight is removed from the tracks, so friction becomes less effective, unless there is high friction material on the bottom of the frame.

Alternatively, they could attach a robotic welding arm to each side and have steel plates which are bolted on to the frame be welded to the deck. Probably unnecessary.

Offline gospacex

  • Senior Member
  • *****
  • Posts: 3024
  • Liked: 543
  • Likes Given: 604
Just glue sandpaper to the bottom surface of the Grabber.

Offline JamesH65

  • Full Member
  • ****
  • Posts: 1559
  • Liked: 1739
  • Likes Given: 10
To me, simple rubber on the underside would increase fraction dramatically, but TBH, that thing must weigh at least 10000kg and won't be any easy thing to move even when holding the stage, even with just steel on steel.

Steel on steel, particularly when wet is a bit slippy.

The simplest answer is to leave the tracks in contact with the deck - that would probably be enough to prevent it moving.

The alternative would be dense rubber pads on the underside of the octagrabber, but all they would do is act as a substitute for the tracks if the tracks were lifted, so why bother lifting the tracks?

The slight issue about rubber pads on the underside of the octagrabber would be that if the tracks were partially retracted and it tries to move, the pads would be ripped off.

Similarly, the fitting of pads would increase the maximum height of the octagrabber - for example, 1" thick pads would increase the height accordingly, which could create an issue trying to get under a stage with fully-collapsed crush cans.

Simplest answer is to rely on the tracks for friction, which has the additional benefit of keeping the overall height lower.

My thinking is they rely on gravity and friction, but they do need to bring the frame into contact with the deck, because the tracks alone are not stable enough, but in so doing some of the weight is removed from the tracks, so friction becomes less effective, unless there is high friction material on the bottom of the frame.

Alternatively, they could attach a robotic welding arm to each side and have steel plates which are bolted on to the frame be welded to the deck. Probably unnecessary.

I suspect that the surface areas of the tracks is less than that of the steel plate, so rubber on the underside and lifting the tracks would be a win. However,without a diagram, who really knows.

Online FutureSpaceTourist

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 48176
  • UK
    • Plan 28
  • Liked: 81677
  • Likes Given: 36941
Quote
I went to @PortCanaveral to visit @SpaceX #OCISLY since it's been a while. I was greeted with autonomous open arms. Yes, we miss you too!

https://twitter.com/julia_bergeron/status/911311757947412481

Online FutureSpaceTourist

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 48176
  • UK
    • Plan 28
  • Liked: 81677
  • Likes Given: 36941
Quote
I do believe that is Rhoomba sitting on the dock. I guess it is still in repair status.

https://twitter.com/julia_bergeron/status/961269841456979969

Online FutureSpaceTourist

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 48176
  • UK
    • Plan 28
  • Liked: 81677
  • Likes Given: 36941
Apparently picture was taken yesterday

https://twitter.com/octagrabber/status/975699747477557248

Online FutureSpaceTourist

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 48176
  • UK
    • Plan 28
  • Liked: 81677
  • Likes Given: 36941
Some aerial views of OCISLY taken a couple of days ago with octagrabber on deck. From about 1:50 in the video:



Hopefully getting an outing with TESS launch?

Offline whitelancer64

Should we expect to see TESS's booster secured with the octograbber?
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline vanoord

  • Full Member
  • ****
  • Posts: 693
  • Liked: 450
  • Likes Given: 106
Presumably if they have the OctaGrabber on board and functional they'll use it.

Given it got set alight after they'd used it once, it seems likely that the fact they did rebuild it suggests it's a concept thought to be worth persisting with.

Offline chalz

  • Full Member
  • **
  • Posts: 201
  • Austrangia
  • Liked: 104
  • Likes Given: 1668
Yep they used it. The rocket was standing on the barge on Saturday without a crane hooked up with Octo jacked up underneath.



Also it looks like they got both fairing halves.

Offline AncientU

  • Senior Member
  • *****
  • Posts: 6257
  • Liked: 4164
  • Likes Given: 6078
Good shots to check stability in the wind.  Almost no motion can be seen relative to stable background structures when looking near top of stage (grid fins shot particularly).
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Joffan

I see the Octocrab's frame sits on the deck when it's holding the booster. I wonder if that is lowered first when the Octocrab gets in position or is part of the process of taking some weight of the booster - as the weight comes on the struts, the frame goes down against springs.
« Last Edit: 04/22/2018 04:00 pm by Joffan »
Getting through max-Q for humanity becoming fully spacefaring

Offline vanoord

  • Full Member
  • ****
  • Posts: 693
  • Liked: 450
  • Likes Given: 106
Interesting to compare how high off the deck this core is compared to the first time OctaGrabber was used:

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

Offline deruch

  • Senior Member
  • *****
  • Posts: 2422
  • California
  • Liked: 2006
  • Likes Given: 5634
Over the last couple of launches, I've been trying to remember to check when the boosters return on OCISLY.  And I may have missed one, but so far I don't remember ever seeing the grabber bot using all 4 arms to hold a booster.  Each time I've been able to see it in use, it's always been with just 3 of the 4 arms engaged.  Have others noticed this as well?  Or have I just not seen the best pictures? 
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 13463
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 11864
  • Likes Given: 11086
Over the last couple of launches, I've been trying to remember to check when the boosters return on OCISLY.  And I may have missed one, but so far I don't remember ever seeing the grabber bot using all 4 arms to hold a booster.  Each time I've been able to see it in use, it's always been with just 3 of the 4 arms engaged.  Have others noticed this as well?  Or have I just not seen the best pictures? 
It almost looked like only 2 this time? This got some discussion in the Facebook SpaceX group but I didn't see any firm theories why. Are they testing how secure it is with less than 4 arms? That's a good thing to know because there will be mechanical failures from time to time
"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 mme

  • Full Member
  • ****
  • Posts: 1510
  • Santa Barbara, CA, USA, Earth, Solar System, Milky Way Galaxy, Virgo Supercluster
  • Liked: 2034
  • Likes Given: 5381
Over the last couple of launches, I've been trying to remember to check when the boosters return on OCISLY.  And I may have missed one, but so far I don't remember ever seeing the grabber bot using all 4 arms to hold a booster.  Each time I've been able to see it in use, it's always been with just 3 of the 4 arms engaged.  Have others noticed this as well?  Or have I just not seen the best pictures? 
It almost looked like only 2 this time? This got some discussion in the Facebook SpaceX group but I didn't see any firm theories why. Are they testing how secure it is with less than 4 arms? That's a good thing to know because there will be mechanical failures from time to time
Looks like 3 to me: https://twitter.com/ken_kremer/status/1040025868544946176
Space is not Highlander.  There can, and will, be more than one.

Offline deruch

  • Senior Member
  • *****
  • Posts: 2422
  • California
  • Liked: 2006
  • Likes Given: 5634
Over the last couple of launches, I've been trying to remember to check when the boosters return on OCISLY.  And I may have missed one, but so far I don't remember ever seeing the grabber bot using all 4 arms to hold a booster.  Each time I've been able to see it in use, it's always been with just 3 of the 4 arms engaged.  Have others noticed this as well?  Or have I just not seen the best pictures? 
It almost looked like only 2 this time? This got some discussion in the Facebook SpaceX group but I didn't see any firm theories why. Are they testing how secure it is with less than 4 arms? That's a good thing to know because there will be mechanical failures from time to time
Looks like 3 to me: https://twitter.com/ken_kremer/status/1040025868544946176

So, it looks like they finally used all 4 arms on the octagrabber to secure a booster on the ASDS!  I'm not positive this is the absolute first time, but I believe it is.  Also it looks like some of the arm hardware has changed a bit since the original debut.  These pics are from Tom McCool's coverage of the Es'Hail 2 booster return via Twitter. 

https://twitter.com/cygnusx112/status/1064590202470100994

https://twitter.com/cygnusx112/status/1064602746664423425
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1