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In this answer to What are the lines on the wheels of the Perseverance rover called? Are they different than Curiosity's? and in sources linked therein we've learned that the lines across the business faces of NASA rovers' wheels along the axial direction are called grousers and that the shapes on Perseverance's wheels are indeed "wavy" rather than chevron-like on Curiosity's wheels.

Said waviness is shown in the linked question.

Question: Why exactly are Perseverance's wheel's grousers wavy? What insight was gained through experience with Curiosity and simulations on Earth that led to this new and insightfully wavy shape?


Obligatory edit:

The first line of this question already links to the proposed and rejected duplicate, and comments there acknowledge that an actual reason is not known. Thus I've split this aspect off as a new question. Luckily, this question here is now in the process of being answered here and no trace of this answer can be found there.

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The answer, I think, is almost certainly to reduce stresses associated with the sharp ends of the chevrons in the grousers, although the wheel designs differ in other details as well (see below).

As is well known, Curiosity has suffered a significant amount of damage to its wheels. Quoting from the reference above:

The tears result from fatigue. [...] The stresses from metal fatigue are highest near the tips of the chevron features, and indeed a lot of tears seem to initiate close to the chevron features.

(Note that there are punctures in the skin as well, which are I believe not fatigue-related).

It's well-understood that stresses are high around sharp corners in structures, and thus avoiding them can reduce stresses, and that this can result in fatigue failures. Famously the de Havilland Comet suffered from fatigue failures which caused a number of accidents: an extensive document on this is here (PDF link). These fatigue failures were caused by high stresses around the corners of the windows in the aircraft, which were square. The aircraft was then redesigned with round windows, which solved the fatigue problem. None of this was helped by fatigue not being well-understood at all at the time. (Amazingly, Nevil Shute's novel No Highway describes fatigue failures in aircraft, and predated the Comet disasters. Shute was an aircraft designer.)

So I believe that avoiding the chevron pattern avoids the sharp corners with associated high stresses which have caused trouble with Curiosity's wheels, although they have not been the only source of trouble. However I have not been able to find direct confirmation of this, and there are other design changes as well: this page describes some of the changes, which include the tire being thicker, presumably to reduce puncture damage.


A couple of entirely unsourced notes: one feature that is noticable (and is documented) is that there are more grousers on the new wheels than on the old ones: the spacing is smaller. This will do at least two things: it will mean that the load on the wheel will be spread over more grousers, thus reducing the stress around each grouser, and it will also mean that any stone which can get between the grousers in order to puncture the wheel structure needs to be smaller, as the spacing is smaller. Both of those factors are clearly a good thing, although they must have cost mass.

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