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

[fredk]

Here's a worrying photo from S564.

Nothing new there - that tear has been there for months.

[Zeke4ther]

These are not the 'droids you are looking for, move along...

[Gerald]

Here's a worrying photo from S564.

One of the fissures seems to have propagated a little bit since Sol 513, but not much (distorted Sol 564 inset in Sol 513 subimage):

[neo56]

Curiosity posing in front of Mount Sharp on sol 564:

[atomoid]

SOL 631 lodged rock (another view).. didnt see any mention of this elsewhere or i wasnt paying attention..., perhaps it has dropped off by now ...unless its lodged in there whreel well!
EDIT: fell out sometime before sol635

[Gerald]

Hole opened in the left middle wheel between Sol 660 and Sol 667:

[elakdawalla]

Ouch. I noticed the last time I mapped wheel wear that the middle wheels appeared to be accumulating new tears more rapidly than the front ones.

[Gerald]

That has been a drive of about 500 meters; thus roughly extrapolated, we should be prepared to about 5 to 10 additional similar tears or holes till Murray Buttes - although we've always to look with precaution on extrapolations.
Not really frightening under normal circumstances; we'll have to get accustomed to it ... and keep the eyes open.

[climber]

In this case we can see that the place was already damaged so, I guess, it was "easily" removed. Actually, we can't see yet whether the missing part is torn inside the weel or has been lost. Do you think there is any change of loosing a torn part of a weel? If yes, we'll have to look closely in the rear direction to see if we can see it.

[Gerald]

The upper left fragment (in the image) is evidently torn inside. I didn't find immediate evidence yet, that this does hold for the lower right fragment, too. But the aluminium alloy should be sufficiently ductile to make it more likely, that no large fragment is lost.
A potentially lost fragment should behave similar to a pebble, cause some minor loss of weight of the rover, but without obvious implications to functionality.

[jmknapp]

I noticed the last time I mapped wheel wear that the middle wheels appeared to be accumulating new tears more rapidly than the front ones.

A paper Performance comparison of rough-terrain robots—simulation and hardware has these diagrams of force on the wheels of a MER-type rocker-bogie design going over a step obstacle:




At least in that case it looks like the middle wheel experiences the greatest forces & the front wheel has it the easiest. The peak force on the middle wheel is when the rear wheel climbs the step.

[elakdawalla]

I don't have access to that journal, unfortunately. That's a cool graph. Are the "front" wheels in this journal article on the bogie, or the rocker? I know that the rocker-bogie suspension system performs better bogie-first -- the JPL rovers are all built "backwards" so that if they get into trouble they're better-positioned to extricate themselves. But the graph is labeled "MER" so maybe it is rocker-first.

[fredk]

That paper states

Note that, contrary to the real MER, the front side of the simulation model was chosen at the bogie side

[jmknapp]

Weird drive on sol 667--only 1.2m spread out over almost 2 hours. The speed plot shows it was in four equally-spaced bumps, and MASTCAM L and MAHLI took images of the wheels along the way. Worrying about the wheels has been officially deregulated.

It'd be interesting to see 4 images of a particular wheel combined to "unroll" it into a continuous ribbon showing the wear pattern.

[elakdawalla]

That's not weird, that's a standard wheel-imaging drive -- they do those every few hundred meters in order to monitor damage. They seem to be performing them on weekends for the most part. They recently made a tweak to their wheel-imaging routine: It used to be they took MAHLI images centered on each wheel (6 images), in 4 different positions. Now they are taking images of middle and rear wheels together (so only 4 images total), in 5 different positions, which gives them a more complete survey. They've also added Mastcam and MARDI documentation.

Also, note this talk planned for the 8th Mars conference in Pasadena:

CURIOSITY'S FLAT TIRE ON MARS AND WHAT WE DID ABOUT IT
This event is presented in conjunction with the Eighth International Conference on Mars.
The speakers for this event are, John Grotzinger, Mars Science Laboratory project scientist, and Matt Heverley, Curiosity Rover driver
The lecture is free and open to the public. No tickets or reservations are required.
Wednesday, July 16, 7:30 p.m., Beckman Auditorium

I'm not sure I'm going to be able to go, sadly.