

Curiosity wheel damage: The problem and solutions - mholt
http://www.planetary.org/blogs/emily-lakdawalla/2014/08190630-curiosity-wheel-damage.html

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hartator
I don't get the "odometry marker". Why they are not just counting the regular
pattern of the wheels and do some approximations? And another subject,
actually the odometry markers seems pretty solid, maybe they should have made
the wheels of only odometry markers.

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mholt
My guess: the odometry markers not only measure distance, they also provide
traction. They're stronger for basically the same reasons I-beams are strong.
The shape of the cross-section is extremely durable through certain types of
stresses. In the case of the wheels, they're stronger against punctures and
bending depending on the direction of the torque.

~~~
pdkl95
There could be value in having _different_ types of surfaces on the wheel as
well. The odometry region might be able to handle some problems that the
smooth regions cannot (and vice versa).

~~~
fit2rule
The odometry region is a danger zone for exactly the same problem described in
the article: big pointy rocks that don't move - at all - can get stuck in the
holes, and suddenly rover is stuck on that big pointy rock.

Whats needed, in my humble opinion, is variant chevron patterns which
distribute the puncture load evenly across the contact surface .. seems that
the chevron itself is a big pointy thing, and when it gets close to another
big pointy thing - i.e. Mars itself - then the tearing happens. This is sort
of a 'duh', though, I have to say .. perhaps the Mars rovers should be tested
in places like the Kimberly region of North-western Australia, a wild and
hostile landscape where - essentially - massive piles of steely/iron ore rock
and associated minerals have been practically welded into place onto the
planet across the wide, hostile, Mars-like region .. I've punctured many a
wheel there myself, dang it, in that part of the world.

Anyway, the wheel design and its problems/lessons-learned is indeed
fascinating. This article was a real blast for this remotely-operated robot
fan.

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dalke
This is not a 'duh'. Curiosity is at the edge of what we can build and place
on the surface of Mars. It's very carefully designed to handle the expected
conditions on Mars. As the article points out in section 5, it's possible to
make the wheels thicker, and handle a wider amount of surface conditions, but
that comes at a cost. Not only would it be more expensive to deliver to Mars,
but

> a major constraint arose from a tricky moment in the landing sequence, at
> the moment that the wheels deployed, while the rover was suspended from the
> bridle underneath the descent stage. The wheels' sudden drop imparted
> substantial forces on the mobility system, and keeping wheel mass as light
> as possible reduced those forces to manageable ones. There were other
> factors that made it important to keep wheel mass low.

Making Curiosity handle all of the worst (dry) terrain on Earth might end up
with a machine that cannot be landed on Mars, or a reduced science capacity.

Remember also that it was designed for a two year mission. That was a success.
Now it's on an extended mission.

~~~
fit2rule
In my opinion the condition of the wheels at this point in the mission profile
_is_ a 'duh', absolutely, but not necessarily a 'dud'. The investigators
themselves admitted they were surprised to learn that the design of the
cantilever, combined with 'sharp pointy rocks on Mars that have been stuck in
place for millions of years', as well as what is a near-obvious flaw in the
chevron design, produced the current conditions. Lesson learned, but hardly a
surprise.

I'm not saying it was a failure, just that the cause of the problems is hardly
surprising, or even unpredictable given the circumstances. But, as always,
design and budget constraints produce a panoply of ways things can get -
eventually - busted in production ..

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dalke
For those following the topic, this is the article from 2014/08/19 and
previously posted here at
[https://news.ycombinator.com/item?id=8203876](https://news.ycombinator.com/item?id=8203876)
. There's nothing new.

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SchizoDuckie
This is the coolest thing i've read in a long time. What a world we live in,
where we can send software updates to Mars to fix our robot.

