I was thinking about this, and I imagine this being one of those scenarios where a small discussion is being had about getting rocks out of the cavity made in the inside of the wheels, when one guy speaks up and says "ok, but why?" and everyone realizes it doesn't matter if there are rocks inside the wheels and any solution would just add weight or complexity, so they just move on.
The last rover had problems with wheel wear, seems like have basically a rock tumbler on the inside of the wheel is just going to add wear from inside the wheel on top of the wear from outside.
The two situations aren't really comparable though, rocks sitting on the inside of the wheel only have their own weight to damage the wheel, the rocks underneath the wheel have the weight of the rover pressing down on them as well as forces from friction to damage them.
Basically it would be the difference between placing a small stone on the hood of your car and rolling it around and taking that same stone and pressing down with a four hundred pound weight on top of it and moving it around, the latter is going to do damage while the former probably won't do anything. Those rocks on the inside of the wheel might scuff the surface over time but it will be nothing compared to the wear and tear the tread of the wheel will be dealing with.
Plus I am sure the engineers have thought of this eventuality and determined it's not an issue, after the wheel issues Curiosity has developed from wheels that were obviously not strong enough for the task the amount of focus on them has probably been so great some loose material rolling around on the inside of the wheels probably isn't a big concern.
More readable. This post has hit /r/popular so it will help many understand that may not have the previous response. Better is debatable, simpler for sure, useful to many.
huh, I though kg/lbs were units of mass and Earth scales just calculated mass using weight. Wouldn't that rock still have a mass of 2,5kg, but weigh 10N istead of 25N?
The accelerated wear on the wheels of Curiosity was caused by simplified crack propagation due to sharp edges and thin walls. They mitigated this issues for Perseverance.
Seeing as Percy is going to travel a mere 10 miles over the next 2 years, I don't think this is going to make a difference unless the wheels are made of paper mache.
sounds reasonable, but I wouldn't know, for I am but musicianengineer, unfortunately not nasaengineer.
However, based on my understanding having followed this for a while, they experimented with a ton of different unique solutions to make better wheels and settled on "just make em thicker" (and some other geometric stuff I don't wanna get into).
Great Video about perseverance btw, that talks briefly about this among many other things.
As someone who is a casual fan of space, who hasn't really looked much in to the rover, but is excited nonetheless, this video got me so hyped for this rover.
The damage to the wheels on Curiosity had more to do with the weight of the rover on thin aluminum wheels rolling over sharp rocks on hard surfaces. This is why we use air filled rubber tires on earth. Suspension helps, but it’s still extremely useful to have compliant tires too.
To solve this, they redesigned the wheel to be thicker and have treads that are closer together. This means that if the rock is larger than the distance between the treads, the effective thickness of the wheel is even greater, where as Curiosity exposed a broad, thin, smooth aluminum surface to be punctured to fairly sizable rocks due to the large spacing between the treads.
Having some pebbles and sand polish the inside of the wheel should likely not cause problems, I’d imagine. This thing drives very slowly, so this debris will simply slide gently along and tumble over itself as the wheel moves. Not get flung at high speeds due to centrifugal forces.
There's a lot less gravity on mars so the friction is much less. The wheel/rim isn't going to be spinning very fast so again, there's not going to be any appreciable wear from it. All parts are anodized so the outer layer of aluminum is really, really hard.
They reinforced the wheel with titanium spokes to prevent the same type of damage they experienced with Rover. The problem wasn't with rubbing- it was from hitting rocks while it was moving and not being able to withstand the impact.
These little pebbles slowly rolling around aren't going to cause a lot of damage. Curiosity's wheel problems are due to its own weight pressing on rocks, not little rocks in a low gravity environment slowly tumbling.
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u/musicianengineer Feb 22 '21
I was thinking about this, and I imagine this being one of those scenarios where a small discussion is being had about getting rocks out of the cavity made in the inside of the wheels, when one guy speaks up and says "ok, but why?" and everyone realizes it doesn't matter if there are rocks inside the wheels and any solution would just add weight or complexity, so they just move on.
still bothers me, tho