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A comment on Breaks Observed in Rover Wheel Treads.

Re:Breaks Observed in Rover Wheel Treads by JetDogRush on Wednesday March 22, 2017 @09:17AM (#13930625)
This seems dramatic, but there is a ton of life left in the wheels. Some of my colleagues performed life testing on the wheels after we first discovered the cracks and found the rover is capable of driving around on the titanium support struts even after the aluminum wheels have completely disintegrated. We've got a long way to go yet!
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Re:Breaks Observed in Rover Wheel Treads by kahnpro on Wednesday March 22, 2017 @09:35AM (#13930733)
If Kerbal Space Program taught be anything about space, it's that most problems can be solved with struts.
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Re:Breaks Observed in Rover Wheel Treads by marcosdumay on Wednesday March 22, 2017 @09:47AM (#13930822)
It's a completely non-realistic game. It's lacking of duct tape is inexcusable.
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Re:Breaks Observed in Rover Wheel Treads by andygates on Thursday March 23, 2017 @09:46AM (#13939651)
There's not a duct tape mod?
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Re:Breaks Observed in Rover Wheel Treads by zurp on Wednesday March 22, 2017 @11:48AM (#13931854)
Darth Bubba: "I find your lack of duct tape disturbing."
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Re:Breaks Observed in Rover Wheel Treads by JetDogRush on Wednesday March 22, 2017 @09:38AM (#13930757)
If only Curiosity were as fast as the KSP rovers... top speed is somewhere around 100 meters/hour, and usually more like 40!
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Re:Breaks Observed in Rover Wheel Treads by pavel_lishin on Wednesday March 22, 2017 @10:59AM (#13931439)
The flip side is that Curiosity has never, to my knowledge, flipped over and tumbled at near-escape-velocity, shedding solar panels and scientific instruments as it goes.
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Re:Breaks Observed in Rover Wheel Treads by TeMPOraL on Wednesday March 22, 2017 @09:55AM (#13930881)
Should have strapped an SRB on the rover.

Reminds me; I wonder just how much ion engines are overpowered in KSP compared to their real-life equivalents. Or, put differently, if one could replicate a hovering Minmus rover I made in KSP (which used ion engines to stay afloat for a long time).

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Re:Breaks Observed in Rover Wheel Treads by creshal on Wednesday March 22, 2017 @11:05AM (#13931487)
KSP: 4200s Isp, 2000 N thrust

Real life: 2000-20000s Isp, 0.01-2.5 N thrust

KSP's ion engines are hilariously overpowered in terms of thrust (and thrust-to-weight ratio) and power efficiency. It's a necessary change, however, since KSP is ill-suited for transfer burns several months long.

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Re:Breaks Observed in Rover Wheel Treads by jerf on Wednesday March 22, 2017 @10:59AM (#13931444)
Minmus surface gravity is 0.491 m/s^2; current ion drives thrust with a couple hundred millinewtons, so I don't think a drive could even support itself against that level of gravity let alone with power and a ship attached.

However, we currently design our ion drives for power-to-thrust efficiency and long-term effectiveness. I'm not sure what we could get if we designed them for maximal thrust. Especially since in real life, right now the answer to "Do you want a 'maximal thrust' ion drive?" is pretty much "Well, have you considered using... not an ion drive?", so I'm not sure I've ever seen a treatment of that question based on current tech.

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Re:Breaks Observed in Rover Wheel Treads by creshal on Wednesday March 22, 2017 @11:06AM (#13931498)
> I'm not sure what we could get if we designed them for maximal thrust.

Probably something with a worse specific impulse than a chemical engine.

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Re:Breaks Observed in Rover Wheel Treads by Symmetry on Wednesday March 22, 2017 @01:44PM (#13933047)
The problem is less our ability to make the drives themselves have a high TWR (thrust to weight ratio) so much as that the power generation necessarily required to run them is very heavy. See here:

http://hopefullyintersting.blogspot.com/2015/03/rockets-elec...

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Re:Breaks Observed in Rover Wheel Treads by skykooler on Wednesday March 22, 2017 @02:50PM (#13933612)
The VASIMR engine is sort of that - an ion engine designed to be able to increase thrust when needed.
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Re:Breaks Observed in Rover Wheel Treads by Declanomous on Wednesday March 22, 2017 @12:07PM (#13932036)
That really is slow. My brain interpreted that as 100 m/s, and then 40 m/s, and I read the sentence a few times trying to figure out if you meant that rovers go that fast in KSP before I figured out it said 100 m/hour.
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Re:Breaks Observed in Rover Wheel Treads by oconnor663 on Wednesday March 22, 2017 @03:28PM (#13933970)
The KSP subthread makes every space article twice as much fun :)
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Re:Breaks Observed in Rover Wheel Treads by jschwartzi on Wednesday March 22, 2017 @05:27PM (#13935142)
That's funny. It's taught me that if you make a rocket long enough, no amount of struts will prevent it from wobbling itself completely apart within 60 seconds of blast off.
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Re:Breaks Observed in Rover Wheel Treads by vkou on Wednesday March 22, 2017 @06:52PM (#13935793)
Struts won't, but turning off automatic stability 'assistance' will!
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Re:Breaks Observed in Rover Wheel Treads by valuearb on Wednesday March 22, 2017 @11:26AM (#13931662)
They don't build 'em like they used to!

They used to break within days or hours.

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Re:Breaks Observed in Rover Wheel Treads by londons_explore on Wednesday March 22, 2017 @10:41AM (#13931288)
When they break though, I could imagine them getting tangled around things immobilizing the robot.
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Re:Breaks Observed in Rover Wheel Treads by JetDogRush on Wednesday March 22, 2017 @10:50AM (#13931376)
You're right - you can see the cable harnesses to the drive actuators in the original article. A major concern would be if a big flake bends inward and manages to sever those wires.
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Re:Breaks Observed in Rover Wheel Treads by cr0sh on Wednesday March 22, 2017 @01:33PM (#13932934)
> found the rover is capable of driving around on the titanium support struts

Anyone who has watched enough of the COPS television show could have told ya that you can go quite far on just the rims.

Heck, check out what some normal people do on /r/justrolledintotheshop...

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Re:Breaks Observed in Rover Wheel Treads by tropo on Wednesday March 22, 2017 @07:05PM (#13935895)
So, I don't get it. There are obvious issues here:

Angular ribs cause stress points. Good CAD software should tell you this.

Some metals are able to flex a small amount repeatedly, forever, without cracks. For other metals, "small" is just zero. Any flexing will eventually create cracks. Aluminum is a bad metal. Titanium is a good metal. Steel varies; unfortunately the good types tend to corrode.

You have aluminum over titanium. Putting dissimilar metals in contact encourages corrosion.

Mars is known to contain perchlorate salts. This is horrible for corrosion. Note that corrosion encourages crack propagation. Oh, and Mars has other stuff to not mix with aluminum: iron oxide and chlorides.

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Re:Breaks Observed in Rover Wheel Treads by anotheryou on Thursday March 23, 2017 @06:50AM (#13938691)
They didn't test against pointy embedded rocks, because there where few of those where the small rovers had been.

The main problem was the angle of the front and legs: if you drag a rolling suitcase up a curb it's all good, but when you try to push it up, you can generate forces much higher than the weight of the suitecase. Same happened to the rover.

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Re:Breaks Observed in Rover Wheel Treads by anotheryou on Thursday March 23, 2017 @06:47AM (#13938678)
I read the biggest danger is something pointing up and cutting the exposed cable running to the central motor controller, potentially shorting it. That would stop all motors on the rover (wheels and a few more).
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