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Wheel Damage Adding Up Quickly For Mars Rover Curiosity
An anonymous reader writes: The folks in charge of the Mars rover Curiosity have been trying to solve an increasingly urgent problem: what to do about unexpected wheel damage. The team knew from the start that wear and tear on the wheels would slowly accumulate, but they've been surprised at how quickly the wheels have degraded over the past year. Emily Lakdawalla at the Planetary Society blog has posted a detailed report on the team's conclusions as to what's causing the damage and how they can mitigate it going forward. Quoting: "The tears result from fatigue. You know how if you bend a metal paper clip back and forth repeatedly, it eventually snaps? Well, when the wheels are driving over a very hard rock surface — one with no sand — the thin skin of the wheels repeatedly bends. The wheels were designed to bend quite a lot, and return to their original shape. But the repeated bending and straightening is fatiguing the skin, causing it to fracture in a brittle way. The bending doesn't happen (or doesn't happen as much) if the ground gives way under the rover's weight, as it does if it's got the slightest coating of sand on top of rock. It only happens when the ground is utterly impervious to the rover's weight — hard bedrock. The stresses from metal fatigue are highest near the tips of the chevron features, and indeed a lot of tears seem to initiate close to the chevron features."
The things are the thinnest element in the entire lander. When I first saw those wheels, I just shrugged and figured they knew what they were doing. But the reality seems to be that they stuck with some sort of legacy design and somehow nobody ever asked the obvious question about those miserably thin wheels.
Though maybe I should instead be celebrating the fact that they didn't get their metric crossed with their imperial.
For a three month mission, this rover is performing fantastically beyond expectations. That is is breaking down now, two years after first landing, is not exactly unsurprising.
Sure, we should do whatever we can to continue its mission -- the knowledge being learned is still impressive but let's not expect it to perform more than eight times its original mission....
Still unsure as to why they didn't go with polyurethane or hard plastic wheels or similar. Probably about the same weight as the alloy ones, much less susceptible to fatigue.
Might be hard to find something that's good for those temperatures, but surely not that hard. Or were they expecting more sandy areas?
You are in a twisty maze of processor lines, all alike.
There is a lot of hype here.
Solarpanels ? Curiosity is powered by an RTG not solarpanels.
http://en.wikipedia.org/wiki/Curiosity_%28rover%29
You are thinking about Spirit and Opportunity, whom both have solarpanels.
Spirit
Obligatory, because it's beautiful.
polyurethane or hard plastic
Worried about UV damage?
is somehow involved.
Seriously, Spare Tires? Or spare belts for tires so that the rover can re-tread itself.
Simply build a wheel changing robot and launch it to Mars.
If it's too difficult, I can't understand it !
Pic of the wheel ...
http://www.garrettbelmont.com/...
The first time when I saw the wheels I was wondering why the hell they spend so much money to send up a robot to Mars and then equip that thing with such flimsy wheels
And I did post question here on /, and there were people (NASA fanbois, perhaps) defending those flimsy wheels
Muchas Gracias, Señor Edward Snowden !
I am guessing that part of the reason for an all-metal milled wheel is because of the (largely) unshielded RTG power source which Curiosity uses may seriously degrade organic-based materials.
Could someone with more knowledge of materials near RTG sources comment?
No sig. Move along - nothing to see here.
"...how they can mitigate it going forward", and presumably backwards too!
The thousands of microscopic missiles launched at the rover to stop it anhialating more of their tiny cities is finally paying off. If one of them only had an old macbook and some way of getting to its core....
Aluminum does not have a fatigue limit. That is, no matter how beefy you make an aluminum part, after enough cyclic stresses it will suffer fatigue failure. This is why airframes are retired after about 100,000 pressurization cycles - to avoid the fate which befell the de Havilland Comet.
Other materials like steel or titanium can be designed so it can withstand an infinite number of stress cycles and not fatigue. Given the nature of the mission and power source (multi-year if not multi-decade operation on another planet with no hope of human intervention if something should go wrong), they really should have allocated sufficient weight budget for non-aluminum wheels. This is basic materials science that every undergrad mechanical engineer learns. I was very surprised when I heard they were going with thin aluminum wheels on this rover.
I wish I had the time to analyze wheel design. Why don't some of you submit to Nasa? Like those Apple analysts (but who actually get paid) reality differs from theory...
I should have gone with the Michelins
My thought exactly ...
"Oh, no! The item we built is starting to fail after it's had 40 times the planned usage!"
That's not a poor design choice ... that's a *fantastic* problem to be having.
Build it, and they will come^Hplain.
To all you idiots who think you could have done do a better job, read Emily's article. There were serious weight constraints for the wheels that effected everything from EDL to operations. Any huge engineering project is full of tradeoffs. Hindsight is 20/20.
Launch and land a "pep boys" on mars...
Do not look at laser with remaining good eye.
The biggest problem is the curvature of the wheels is concentrating all of the weight of the vehicle on the center of the wheel, and not only that, but with the tread design, all the force is concentrated on a spot about 2 square millimeters. They just need to add a rib going down the middle like bicycle tires.
I love how the retards are bitching because the probe that got launched to Mars is starting to have problems after exceeding the design life.
As an embedded systems (electronics/firmware) engineer, I was going to half-jokingly, half-seriously say, "Well, we'll just send a new firmware update to Curiosity to help with the problem." And then of course as I read the article, that was one of the proposed mitigations:
I've been developing embedded systems for more than half my life, and I never get bored...
FTFA:
[...] It turns out that there are mechanical aspects of the mobility system that actively shove the wheels into pointy rocks. A wheel can resist the force of one-sixth of the rover's weight pressing down on a pointy rock, but it can't resist the rover's weight plus the force imparted by five other wheels shoving the sixth wheel into a pointy rock. The forces are worse for the middle and front wheels than they are for the rear wheels
[...] If the pointy rock can move, all that pushing force behind it will just shift the pointy rock to one side or another, or it can roll beneath the wheel, and the wheel will get over it without damage. The key to wheel punctures is immobile pointy rocks. If the pointy rock is stuck in place, partially buried, or if it is a pointy bit of intact bedrock, then there's nowhere for it to go
[...] the software requires all six wheels to rotate at a constant rate, even though a wheel climbing an obstacle has a longer path to travel than one traversing flat ground. By implementing a "smart controller" on the wheel current and allowing wheel rotation rates to vary intelligently in response to sensed conditions, they might be able to mitigate the damage.
How much more of the same do they have to search for any way? Spend the next zillion dollars in resources discovering new energy sources for our dying planet. Please.
Rubbers of vulcan perhaps matrixed with metallics or silicone nodules might last for many moons, however.
I don't get what's so hard. Just have Jebidiah Kerman exit the rover and fix the wheel.
Beryllium Copper
http://en.wikipedia.org/wiki/A... I wonder why none thought of those...they look much sturdier and if that mesh fails it will be in spots only... plus with 50years later materials.... look to me they could have done a maybe better job....
What is being done to improve future wheels on rovers and others?
Ant(Dude) @ Quality Foraged Links (AQFL.net) & The Ant Farm (antfarm.ma.cx / antfarm.home.dhs.org).
It's not "bad luck", it's why you explore. If you send out a scout to the east, and he comes back with an arrow in his back, bummer for the scout, but at least you now know the east is dangerous before sending the rest of the troops to the east.
Better we find out about stiff rocks now instead of when humans are driving a rover there, without AAA.
Note this rover is better able to handle sand based on lessons from the last rovers.
Table-ized A.I.