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

[dr_rick]

thank you for this discussion and for the images posted, and in particular that posted by Astro0 9 posts back.

When I was looking at this, I was concerned that, at the end of what appears to be a crack or break in the wheel surface material (unless I have completely misunderstood the image - in which case, please forgive me - this is my first post here), there looked to be a distortion of the wheel surface continuing in the direction of the break, suggesting that a crack continues in that direction. I downloaded the image and fiddled with the contrast (attached) and believe that my initial observation is correct. In terms of monitoring the progress of the damage to the wheel, it will be interesting to see whether the cracking continues in that direction.

modified to make image clearer

Attached thumbnail(s)

 

[fredk]

These two MH wheel views happen to show almost identical faces of the LF wheel - load them up in different windows and flip between them to see the changes between sols 488 and 506 (three shortish drives between them):
http://mars.jpl.nasa.gov/msl-raw-images/ms...0001E1_DXXX.jpg
http://mars.jpl.nasa.gov/msl-raw-images/ms...0000E1_DXXX.jpg
Apart from some new small scratches, there seems to be a new hole near the bottom of the wheel.

(Mods - sorry, I meant to post this in the wheel thread.)
Mod: Done.

[Phil Stooke]

To me it looks like the hole was there before, but with shaded ground behind it instead of illuminated ground.

Phil

[dilo]

Phil, I think fredk is referring to the red-arrow highlighted feature:

The opaque appareance and the straight borders suggests it is a simple light-spot projected from squared opening (windows) on top of the wheel (you can see another spot above it...).

[fredk]

You may be right, Dilo - at first I thought that couldn't be sunlight shining through a hole because the inner wheel surface is quite dark grey, as you can see from the other light spot. But if there are patches of soil sitting on the bottom of the wheel, they would look bright orange when sunlit of course. Once we get a rotated view of the wheel we'll know for sure.

[elakdawalla]

Yeah, I stared at that for a while this morning and couldn't decide either whether it was a new hole or a sunlight patch. I was leaning toward sunlight patch but don't see strong enough evidence to overturn anybody's call either way.

[Greenish]

Looks like the ~1-meter drive on sol 513 was equal to a half-turn of the wheels, with MAHLI imaging of all wheels at 4 positions - I suppose the repeatability test for arm position the other day was with this in mind, though I don't know if we could tell other than from SPICE files if the arm was stowed for each step, or if they found a spot smooth enough to leave it deployed for these small steps. Wonder if they will do the other half-turn next sol, or if those positions are covered by other recent imaging? They downlinked and posted the images quickly, too - about 6 hours after taking them.

The good news is that there's not much discernable difference between sol 490 (right image) and sol 513 (left) on the worst spot on the front left wheel.

[Greenish]

Should have read the news first. From Ken Herkenhoff (full text here):

...Sol 513, which will be dominated by a full set of MAHLI images of wheels. The images will be taken between short drives, to turn the wheels a bit and allow the entire surfaces of the wheels to be imaged....

[Olivier]

Are all the wheels "in sync" ??? i.e. do they all show the same exact number of rotation on a given drive?

Olivier

[charborob]

They would if you were driving in a perfectly straight line on a smooth surface. But on a rugged surface, and with turns, you obviously have different numbers of rotations. For example, during a turn, the outer wheels make more rotations than the inner wheels.

[fredk]

Plus there will always be some wheel slippage, which will be different for each wheel.

[nprev]

I believe that each wheel is independently controlled as well if they emulated the MER design philosophy. Therefore any rotational synchronization in term of identical RPMs (often over several Ms, frankly) would indeed have to be straight-line and frankly coincidental given external factors like slippage.

[elakdawalla]

With all this recent wheel imaging, it really seems like it should be possible to produce a systematic survey of the current condition of the entire circumference of all the wheels. Just throwing that out there in case someone has the time to organize images into such a survey....

[Gerald]

I've ideas for a 0th and 1st approximation of an "undistortion" algorithm for the wheel images. For the 0th approximation three points should be sufficent to retrieve the mantle of an assumed cylindric wheel. A fourth point as parameter may already be sufficient to take account of the perpendicular curvature.

This shouldn't be too difficult to program. May be I'll dare a try on Sunday.

[Astro0]

Yes please Gerald.....'Dare Mighty Things'!