Hey, when Two Guys from Canada both suggest the same thing, they've got to start thinking it might be a good idea.

That's right, eh, you hosers!

Phil

I agree. In this type of terrain we need as much heading control as we can. Once on the parking lot maybe we can relax a bit. If the issue is the number of thermal cycles, not the number of wheel revolutions, then the answer is pretty clear (use it while you can!).

Paolo

Take off!

(With apologies to non-canucks...)

Any thoughts on why the right front wheel seems to be more vulnerable than the other wheels?

1:6 says that the first wheel to get trouble will be the same on both rovers.

I think the odds are actually lower than that - the front two wheels are likely to be a bit more stressed in general so I'd have thought it was closer to a 50:50 chance. But you are right - it's 1 in 6 assuming all wheels are equal which means we can't read anything into it with just two data points.

Maybe even shorter odds. The corners could be be more vulnerable than the middle wheels.

EDIT Nice one helvick, you beat me to it there.

Assuming there are no dependent variables between the wheels. But I think the front wheels had to do more "unfolding" out of the stowed position versus the middle or rear wheels. Maybe that is a factor? Plus, the weight distribution might not be symmetrical, with one side heavier than the other due to the robotic arm (it comes out from the right, correct?) and the pancam mast (front vs back). If MSL's first wheel failure is the right front, then we know there's a conspiracy.

... so how many wheels need to fail before the rover can't rove ?
Would a Left Rear freeze do that?

I actually went to the ISIL to do some testing to answer this question a couple of years ago. For sure this depends a lot on soil type, but in the testing I have done, if you lose two driving actuators you immediately become a lander. Of all the wheels to lose, the front wheels are the one that cause less trouble (the rocker is longer than the bogie) and they can be seen in the FHAZ (the RR can't be seen very well in the RHAZ). Between the rear and middle, losing one of the middle wheels has the advantage of having the same difficulties in driving forwards vs backward and causes less heading change when trying to drive straight. The loss of one of the rear wheels would probably be worst, less visibility in the RHAZ and driving backwards would probably be a mess since you would immediately pop a wheelie effectively driving only with four active wheels.

As a side note, I also tried to drive the testbed on pavement Spirit-like and do typical Opportunity-like turn-in-place and neither of these activities are look pretty to the eye or to the ear: the grinding noise and the amount of deflection on the rocker is amazing!

Paolo

Thanks for taking the time to answer..
.. so wonderfully informative!
Best of luck MER team..,
Eoin

*Sigh* Youtube was just a little bit too late...

I still have nightmares after seeing the engineering model (or maybe it was a simulation, I don't recall) driving with 5 wheels in the "Five Years on Mars" special. Okay, not literally, but ouch... that was painful to see.

Assuming randomness, though, we would expect to see increased signs of wear, such as occasional elevated currents, on the other wheels before too long after the first, right? Is it reasonable to invoke randomness when one wheel has serious trouble long before the others show the slightest sign of trouble?