ROVER WHEELS: Monitoring changes over time, NOTE: Read back through the thread to avoid repeating misconceptions |
ROVER WHEELS: Monitoring changes over time, NOTE: Read back through the thread to avoid repeating misconceptions |
May 16 2013, 08:35 AM
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#1
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Junior Member Group: Members Posts: 22 Joined: 10-August 12 From: Australia Member No.: 6530 |
[MOD NOTE: This thread follows on a post by Ed Truthan containing a MAHLI mosaic of MSL wheels taken on sol 275.]
Ed: zooming in on that marvellous underbelly MAHLI montage, there appears to be further (and previously noted) deformation of the wheel surfaces. Damage is most evident in the view of the front-left wheel inner surface. Such wear has previously been discussed and concerns allayed. Nevertheless, the front left wheel surface *appears* to have been punctured. We've only done 700 meters, and have 7000 more to get to Mt Sharp..... Given that more odometry has now accumulated, is any (re-)new(ed) concern valid? DeanM |
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May 16 2013, 10:15 AM
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#2
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Senior Member Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 |
No, I wouldn't be concerned.
Yes there is a bit of damage, yes there will be 10x as much when we get to Mt Sharp, but the wheels will still be fine to drive on, this was expected. -------------------- |
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May 16 2013, 11:12 AM
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#3
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Forum Contributor Group: Members Posts: 1374 Joined: 8-February 04 From: North East Florida, USA. Member No.: 11 |
Your going to have to regularly reassure us.....it looks bad to the layman. Of course at least the wheels can be regularly photographed as MSL roves accross this amazing landscape .
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May 16 2013, 02:05 PM
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#4
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Founder Group: Chairman Posts: 14448 Joined: 8-February 04 Member No.: 1 |
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May 16 2013, 02:56 PM
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#5
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Isn't the "puncture" merely a glint of light? Could there be anything on Mars hard enough to make a narrow puncture through that much metal?
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May 16 2013, 03:03 PM
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#6
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Senior Member Group: Members Posts: 2547 Joined: 13-September 05 Member No.: 497 |
If the rover is still roving, such reassurance is utterly redundant. That's a nice empirical observation. Somewhere in a review package I expect there's a detailed analysis of how the wheel was designed, with allowable levels of damage, predicted damage and margins. I haven't seen that package and if I had, I couldn't post the details anyway. So any assurance I could offer on this forum wouldn't really be fact-based, but I assume the designers had it under control. Over on nasaspaceflight.com someone proposed a drinking game based on how many times this comes up -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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May 16 2013, 03:06 PM
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#7
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Senior Member Group: Members Posts: 2547 Joined: 13-September 05 Member No.: 497 |
Could there be anything on Mars hard enough to make a narrow puncture through that much metal? I won't speculate on these images, but the wheels are pretty thin (I don't know what the actual number is) and the loads can be pretty high on a sharp rock. Aluminum isn't that hard. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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May 16 2013, 03:13 PM
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#8
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Senior Member Group: Members Posts: 4260 Joined: 17-January 05 Member No.: 152 |
the front left wheel surface *appears* to have been punctured. We've also discussed this before. I still see no clear sign of puncture. The dents may be reflecting bits of bright sky which makes it look like there are punctures.About reasurrances, it would be interesting to hear from someone who knows something about the engineering of the wheels. Does the thin skin covering the circumference of the wheels, which is dented, actually provide significant structural strength to the wheels? Or does the skin just prevent sand and dust from getting into the wheel mechanisms inside, and the raised, narrow, treads are actually providing the main structural strength? In this case the skin could be severely punctured and torn and we could still drive. Edit: scooped by Joe, and thanks mcaplinger for the details. |
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May 16 2013, 03:59 PM
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#9
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Senior Member Group: Members Posts: 1621 Joined: 12-February 06 From: Bergerac - FR Member No.: 678 |
QUOTE The dents may be reflecting bits of bright sky which makes it look like there are punctures. It can't be. We are seeing these things in shadow, and from where there are, impossible to have the sky in sight. Because of the wheel itself, and the rover body. I'm wondering about the material used to build theses wheels. At first, I thought they where designed in the exact same way as the MER's : a metalic monobloc. -------------------- |
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May 16 2013, 05:33 PM
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#10
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Senior Member Group: Members Posts: 4260 Joined: 17-January 05 Member No.: 152 |
Being in shadow means they couldn't reflect the Sun, but they still could see some part of the sky and reflect it. The sky is a big thing so it's hard to block all of it!
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May 16 2013, 07:56 PM
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#11
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Senior Member Group: Members Posts: 2432 Joined: 30-January 13 From: Penang, Malaysia. Member No.: 6853 |
I am sure this wheel debate will roll on for some time (pun not really intended). I have not found the specification for the material for the rover wheels, but judging from the number of dings in the rims we know the material is very ductile, but it appears to be a high performance aluminium alloy. Reassuringly aluminium remains ductile even at extremely low temperatures, but good to see that drives have occurred at mid day when the temperature ranges reduce any fatigue issues created by very low temperatures.
I would not be concerned with small punctures in the rims, after all we already have the 'Morse Code' cut outs, nor would I be concerned with a plethora of additional dings that we can expect during the remainder of its mission, but am concerned about possible 'work hardening' of the material which over time could reduce the ductility of the material that could lead to undesirably issues. I am sure the engineering team and drive planners will remind the science team from time to time that the rover wheels are not designed as rock crushers and that we would like them to last as long as the power supply |
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May 16 2013, 08:02 PM
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#12
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Senior Member Group: Members Posts: 2547 Joined: 13-September 05 Member No.: 497 |
See slide 32 in http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/12-0690.pdf
QUOTE Wheel cleats and surfaces thoroughly tested for odometry, wheel impact, functionality -- localized denting & rupture, ovalization permitted -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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May 17 2013, 09:36 PM
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#13
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Founder Group: Chairman Posts: 14448 Joined: 8-February 04 Member No.: 1 |
It can't be It is. That 'hole' is a dent, the stress of the dent has popped the anodized coating off the inside of the wheel and we have bare aluminum reflecting the sun. That dent isn't in shadow. Those that are can reflect the bright martian sky off them. Just because something is in shadow - it doesn't mean it can't 'see the sky'. Look at it - it's not even the same color as the terrain behind it. And even if it IS punctured - it doesn't matter. Once of the test-bed rovers at JPL had flight like wheels whilst dealing with 3x the effective weight of a real rover. The wheels were punctured, dent ridden, ripped, torn, dinged, bashed, smashed, crunched. You could put your finger thru the holes in places - you could see clean thru them. And they still worked absolutely fine. That testbed now has tougher wheels simply to deal with terrestrial gravity. The lightweight scarecrow rover has flightlike wheels. I'm not sure how long it's going to take until saying 'the wheels are fine' before it gets boring. Infact, I think it might already have passed. |
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May 17 2013, 10:01 PM
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#14
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Founder Group: Chairman Posts: 14448 Joined: 8-February 04 Member No.: 1 |
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May 17 2013, 10:01 PM
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#15
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Senior Member Group: Members Posts: 1621 Joined: 12-February 06 From: Bergerac - FR Member No.: 678 |
Okay Doug, thanks for this very clear explanation
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