ROVER WHEELS: Monitoring changes over time, NOTE: Read back through the thread to avoid repeating misconceptions Options

[anticitizen2]

The wheels have met a few rocks between Sol 34 and now...

[fredk]

Ouch

That gash hasn't changed much over the sols:
http://www.unmannedspaceflight.com/index.p...st&p=208106

[Harder]

Looking at that picture with the “ouch”, I realize all of a sudden that mentally I’ve moved on from any wheel concerns.

The cleats look fine even though a bit of tincan aluminium came off, so what. My frame of mind is “it looks sturdy, good to go for many, many more miles - all as predicted by the UMSF experts (who told me so in no uncertain terms!!) – see the thread.
After all these sols the mission is now getting tantalizingly close to the primary science objectives and that’s what I’m thinking about mostly for MSL.

[Floyd]

We had been a lot on softer terrain, but the stretch from about sol 690-703 went over some nasty sharp rocks in hard surfaces. Not surprised we did some damage over that time frame.

[monitorlizard]

I find myself confused over why MSL's wheels have suffered damage but I never heard any reports of Spirit/Opportunity wheel damage. Is it because MSL is so much heavier than the MER rovers or is it because of different wheel designs? Obviously, Opportunity was a much more benign (less rocky) environment for much of its mission, but I don't think you can say that about Spirit. It all makes me wonder if NASA should go back to the MER wheel design, appropriately scaled up for MSL weight, for the 2020 rover.

[elakdawalla]

The different wheel design is only part of the story. It's mostly because of the terrain. I've heard the caprock at the Curiosity site described as being "like sharks' teeth embedded in concrete." It's not only that the rocks are pointy, but that they don't shift at all when the rover drives over them. Loose rocks sitting on sand get pushed down into the sand as the rover drives over them, substantially mitigating the force they apply to the wheels. Neither of the MERs ever drove over bedrock like this for any substantial amount of time.

[mcaplinger]

It all makes me wonder if NASA should go back to the MER wheel design, appropriately scaled up for MSL weight, for the 2020 rover.

If this had been an option for MSL, it would have been done that way. Simple scaling makes wheel mass go up too much and then there are ripple effects throughout the whole system.

Clearly MSL went a little too far in the lightweighting direction, and I'm sure this will be addressed for 2020, but the problem is more involved than might be immediately thought.

[Gerald]

With the MSL wheel design the rover can drive on, even if a wheel gets hooked in sharp rocks, by sacrificing part of her beauty. The actuators and structural components are strong enough.
With more robust wheels the probability, that a wheel gets stuck in sharp rocks may be reduced, but likely not to zero. So if a wheel of a potential more robust design gets stuck, nevertheless, how does it get disentangled?
A better design may be possible, but it's better to think twice, before changing a design, which is doing its job, although maybe not perfectly in every aspect.

[jmknapp]

I was wondering what happens if cracks propagate all the way across, particularly at several points around the circumference. Does it still hold together?

[Gerald]

Yes, it holds together unless the crack propagates across the cleats along almost all the circumference.
A few posts earlier (Post #217) I've added a link to a video showing were the limits are.

[PDP8E]

Here is an image from SOL-696 that caught my eye.

At first I thought the rover was shedding something, but after looking at the thing's DN numbers, it was about the same as the soil/rocks out in front of the wheel shadow

I am pretty sure it is sunlight from the top right of the wheel (between the rover body or the big holes at the top of the wheel) shining through a rip that is out of our view.

[blake]

I've followed this thread since it first started, when the first holes started appearing in the wheels. And I've had a question from the beginning that I hoped would have been mentioned or answered by now. Now that we have gotten to the Hidden Valley, I am just going to ask it:

Do the holes in the surface of the wheel affect mobility on a sandy surface like Hidden Valley? At what point do holes in the thin aluminum surface start to affect driving over 'dune-like' conditions? I know JPL is spelled out in holes, but if the whole wheel surface was like that, would Curiosity have a harder time in the sand? Clearly the JPL holes interact differently with the sand than the rest of the wheel judging by the tracks left in the sand.

There has been many posts (see below for a small selection) about how the wheels will keep on driving despite the damage. I even remember reading that if a wheel was just spokes, or squared off, it would still drive. But it seems to me that the aluminum 'webbing' between the cleats probably help to float the wheel over the sand. I'm not asking to prove anybody wrong or fear-monger, obviously the wheel isn't just going to fall off, stop turning, etc.; just wondering if there's any information on webbing/sand interactions. I just looked through the thread again and didn't see anybody discuss it (is that enough disclaimers?).

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.

Remember - the wheels were built with several large holes in them....that spell JPL in morse code.
They make little to no difference to traction or surface pressure. Remember - it's 899kg across 6 wheels each with basically the same surface contact patch. It wont change significantly with a few dings and dents in it.

One way to look at this is that the cleats really do most of the work, and they are a lot more robust.

Thanks.

[mcaplinger]

Do the holes in the surface of the wheel affect mobility on a sandy surface like Hidden Valley?

I doubt that the holes at this point affect mobility. But despite many of the historical comments in this thread, it's now obvious that the magnitude of wheel damage was not anticipated, and given the retreat from driving on sand, there is probably something unexpected about that as well. Clearly soil properties and their effect on mobility are very complicated, analysis and testing under Earth conditions can only go so far, and the system is very highly constrained for mass, power, etc.

We'll just have to wait and see how this plays out.

[Don1]

Emily has written an excellent blog post here with a lot of new information about this topic.

My reaction to the article is that the wheel issue seems like a manageable problem as long as the terrain doesn't get worse when we start climbing Mt Sharp. It probably means that Curiosity won't ever drive as far or last as long as Opportunity has, but it doesn't really need to given the proximity of Mt Sharp. And the lab instruments and the drill won't last for ever either.

Fortunately by 2020 there will be a new rover to replace Curiosity.

[Explorer1]

There are several drill bits, I recall. And given the paucity of uses for both it and the sample collecting instruments so far, they might well last as long as Oppy's RAT.