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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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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Nov 30 2013, 08:55 AM
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Member Group: Members Posts: 255 Joined: 28-October 12 Member No.: 6732 |
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?
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Nov 30 2013, 01:01 PM
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#3
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Member Group: Members Posts: 153 Joined: 4-May 11 From: Pardubice, CZ Member No.: 5979 |
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. |
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Nov 30 2013, 08:13 PM
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
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? |
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Dec 1 2013, 12:13 AM
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#5
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
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. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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