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

[MahFL]

Well there you go, if the team were concerned about the wheels, then all of our concerns were validated.
Happy Thanksgiving by the way, to those that are celebrating it.

[mcaplinger]

if the team were concerned about the wheels, then all of our concerns were validated.

In my experience, science teams are no more immune to having concerns about things outside their area of expertise than any other group.

[djellison]

Well there you go, if the team were concerned about the wheels, then all of our concerns were validated.

Sharing a concern doesn't in any way validate it.

And just to repeat ( because seemingly it does bear repeating ) there is nothing to be concerned about. This is expected. It doesn't damage the rovers mobility.

Concerns about wheel damage are not..repeat NOT valid.

[bobik]

Are there any papers on MSL wheel design trade-offs?

[mcaplinger]

Are there any papers on MSL wheel design trade-offs?

Did you read the viewgraph package referenced in http://www.unmannedspaceflight.com/index.p...st&p=200198 ?

Other than that, I don't know of anything. There are some useful quotes in http://news.discovery.com/space/rough-rovi...tear-130522.htm (from May 2013)

“The wear in the wheels is expected,” Matt Heverly, lead rover driver for the MSL mission at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., told Discovery News via email. “The ‘skin’ of the wheel is only 0.75mm thick and we expect dents, dings, and even a few holes due to the wheels interacting with the rocks.”

[Phil Stooke]

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

Phil

[serpens]

So one can posit a scenario where rather than picking up a rock in the wheel as did Spirit, as the skin of the wheel deteriorates Curiosity could pick up a rock jammed between cleats. Wouldn't stop operation but would make for amusing comments.

[Explorer1]

Who says MSL has no sample cache...

[bobik]

It would be interesting to know what other wheel options and materials they considered. What role has the function as the landing gear pads played in the wheel design?

[pospa]

It would be interesting to know what other wheel options and materials they considered.

I'm wondering what is the weight penalty by 2nd set of VSTB wheels with doubled skin thickness.
I guess that using 1,5 mm thick skin instead of 0,75 mm actually used on Mars would eliminate most of wear we see, stop all timorous comments around and would not hurt total rover mass budget significantly.
... maybe for Mars rover 2020.

[djellison]

and would not hurt total rover mass budget significantly.

Well - the wheel rim itself would way about twice as much. I've held one. They're not 'heavy' but there's certainly a few KG's in there.

And you're forgetting - compliance in the wheel is one of the design requirements to take the edge of impacts as wheels drop off rocks etc. Making it 'stronger' just so it doesn't get holes in it ( holes that don't matter ) could very well be counter productive.

Why would you change the design for 2020. They work. They work great. There's nothing whatsoever to suggest they're going to stop working. Why would you invest a second of time, energy, or money - or mass budget - in making them unnecessarily heavier?

[pospa]

Why would you invest ....

If she's gonna work 14+ years and 2020 rover is equiped with the same wheels we'll go nuts from reading endless comments about 'weak torn wheels'.

PS: I talked about doubled 'skin' thickness only (0,75 -> 1,0~1,5 mm), not to strenghten all design elements as radial and axial ribs => for sure not doubled rim weight and less elastic 'wheel-bumper'
PS2: I fully trust engineers that they've made the best optimal design in compliance to all spec and that mobility won't be limited by wheels anytime during prime or future mission extensions.

[djellison]

we'll go nuts from reading endless comments about 'weak torn wheels'.

That could be solved by not posting endless comments about 'weak torn wheels'.

Not by pointlessly changing a vehicle design.

[mcaplinger]

Why would you invest a second of time, energy, or money - or mass budget - in making them unnecessarily heavier?

I'll confess that I've made minor engineering changes just to stop baseless concerns, so let's look at the details. If the wheels are 0.5m in diameter and 0.4m wide, then roughly speaking the outer surface volume is pi*0.5**2*0.4*0.75e-3 = 235 cm3 and its mass (aluminum density is about 2.7 gm/cm3) would be about 600 grams. Doubling the thickness would increase the mass to about 1.2 kg per wheel (times six of course) so the overall mass increase would be about 3.6 kg -- nearly twice the mass (for example) of two Mastcam camera heads. [edit: of course each wheel's mass is greater than 600 gm, this is just a rough cylindrical approximation of the mass of the 0.75mm "skin" of the wheel. For reference, 0.75mm is about 7x thicker than a typical Coke can.]

However, I don't see much evidence that anyone actually read the viewgraphs I linked to. It's worth remembering that unlike MER, MSL relies on the wheels to absorb not only driving loads but landing shock, and the wheels may have to elastically deform a fair bit in the process. Making the wheels thicker would reduce their ability to do so; I'm not sure by how much, but it could be a concern.

[djellison]

And you're forgetting - compliance in the wheel is one of the design requirements to take the edge of impacts as wheels drop off rocks etc. Making it 'stronger' just so it doesn't get holes in it ( holes that don't matter ) could very well be counter productive.

I don't see much evidence that anyone actually read the viewgraphs I linked to. It's worth remembering that unlike MER, MSL relies on the wheels to absorb not only driving loads but landing shock, and the wheels may have to elastically deform a fair bit in the process. Making the wheels thicker would reduce their ability to do so; I'm not sure by how much, but it could be a concern.

Well - I did ;-)