who knows what about the litho model?

[Brainlord Mesomorph]

There’s lots of talk about the aerodynamics model. But who knows anything about lithodynamics model?

I’m talking about variables such as ground hardness, static friction, dynamic friction, gravity, and how they affect the wheels, and speed, and when things explode.

Specifically, I’ve had the rugged wheels pop on me at 41 m /s in one case, and another case survive at 52 m/s. (I’m assuming variables such as ground hardness and friction is the difference.)

Does anyone know anything about the "litho model?"

AHA TIA

Edited October 21, 2015 by Brainlord Mesomorph

[The_Rocketeer]

I don't think there is a lithodynamics model per se. That would suggest that the surface textural properties of the different bodies and biomes varied, and I think this is not the case. I think the different effect you've noticed will be based on the wheel's situational load, which will vary depending on gravity, the vehicle's mass, the number of wheels and the location of the wheel, as well as the vehicle's speed, whether the wheel was steering or under acceleration (i.e. pressing the gas) and whether the ground was smooth/level or sloped/cambered. AFAIK, assuming all other conditions are equal, the particular bit of ground surface of whichever planet you're driving on will make no difference to the wheel's performance.

[Brainlord Mesomorph]

I beg to differ.

Minmus flats are slippery. the mountains less so, the grass at the KSC is softer than the runway etc.

(The rugged wheels pop at a lower speed on the runway than on the grass.)

EDIT: I guess i could be imaging all of that.

EDIT II: IMHO three variables (hardness, static and dynamic friction) would seem to be a minimum for any physics model.

Edited October 21, 2015 by Brainlord Mesomorph

[Signo]

In my experience wheels popping are related to many factors, including angle of impact and extra flexibility you can give to the suspensions - you might want to try to experiment with the "vagani" suspensions (fix your wheels to an ant engine instead of fixing them to the chassis).

[Seajay]

From the title I thought this question was going to be "What's the best altitude for lithobraking". I know that one.

[Retread]

I don't think Minmus is slippery, per se, but the low gravity makes wheel contact tenuous, at best. I've noticed that my Minmus fuel transfer lander/rover (basically an orange tank with wheels and engines) works much better when loaded than when empty.

[The_Rocketeer]

I don't think Minmus is slippery, per se, but the low gravity makes wheel contact tenuous, at best. I've noticed that my Minmus fuel transfer lander/rover (basically an orange tank with wheels and engines) works much better when loaded than when empty.

Agreed. Minmus is slippery because its gravity is low. It's less noticable on the slopes because of the inclines provide parabolic resistance which improves contact and therefore friction. The flats have the opposite effect, with the direction of acceleration being 'upward' relative to the curvature of the surface. The stuff the ground is made of is basically the same, just a different shape.

Incidentally, real ice in space isn't slippery at all. Liquid water can't exist in a vacuum.

[Van Disaster]

IIRC friction is set in the wheel, or something silly ( it'll be in the Unity 4 docs ). The large stock wheels with the yellow paint on the frame didn't used to slip at all on Minmus, which was a bit awkward - I've not tried them now, but I've been driving down 60 degree slopes on Mun with them.

[Ruedii]

Wheels use the Phsyx wheel module, which is far from accurate in it's wheel handling. You can read more about it on various web sites, however, it basically treats wheels like skiis or snowmobile treads, instead of actually treating them like wheels.

Furthermore collisions use the PhysX collision model. Force is calculated nicely, but there is no lithobreaking model to speak of, specifically ground is infinately hard and doesn't give way at all. Any difference in breaking parts on landing has more to do with impact angle changing the impact force, not just the raw speed of the craft. However, landing in anything but water is no different than any other surface other than the angle of the surface.

Edited October 22, 2015 by Ruedii

[Brainlord Mesomorph]

Ah, PhysX, an answer to my question. (I was joking about a lithobreaking model.)

I googled that, there *is* a section in there about different friction for different surfaces. Granted that might not be implemented in KSP.

Because the water is clearly a different surface, I extrapolated grass was a different surface from rock. Given that assumption, I went out and found a lot of evidence for it. (Perhaps it was observational bias on my part.)

Things do seem a lot more “explodey†in the mountains than they do on the grassy flats. But that could be due to how angles change impact force. The fact that the mountains are more pointy this means is a greater chance of one polygon being more perpendicular to your direction of travel or managing to reach between your landing gear and strike the ship.

(and in retrospect: all wheels on all video games I have ever played acted like skis.)

Edited October 22, 2015 by Brainlord Mesomorph

[paul23]

I beg to differ.

Minmus flats are slippery. the mountains less so, the grass at the KSC is softer than the runway etc.

(The rugged wheels pop at a lower speed on the runway than on the grass.)

EDIT: I guess i could be imaging all of that.

EDIT II: IMHO three variables (hardness, static and dynamic friction) would seem to be a minimum for any physics model.

From my experience driving around the static and dynamic friction coefficient are equal (or at least equal, but I doubt anyone would make the dynamic friction coefficient on purpose higher than the static).

[paul23]

Incidentally, real ice in space isn't slippery at all. Liquid water can't exist in a vacuum.

What? Evaporation in space quickly reaches an equillibrium where the few atoms floating around a liquid prevent further evaporation... Even more profound once gravity starts holding everything together. Stating you can't have a liquid in vacuum is about the same as stating you can't have a solid: solids also evaporate (abblate) in vacuum..

[Van Disaster]

If you really want non-exploding wheels, use landing gear. You'll have to use alternate propulsion, but you can go as fast as you like...

[Brainlord Mesomorph]

If you really want non-exploding wheels, use landing gear. You'll have to use alternate propulsion, but you can go as fast as you like...

I have noticed the new steerable wheels. Haven't tried them yet.

[The_Rocketeer]

What? Evaporation in space quickly reaches an equillibrium where the few atoms floating around a liquid prevent further evaporation... Even more profound once gravity starts holding everything together. Stating you can't have a liquid in vacuum is about the same as stating you can't have a solid: solids also evaporate (abblate) in vacuum..

I didn't say you can't have a liquid in a vacuum, I said liquid water can't exist in a vacuum. Since water's liquid state is its most pressurised state, water depressurises into water vapour (gas) and ice (solid). To be slippery, it would have to be changing from solid -> liquid, which would be very difficult without an increase in pressure, i.e. not a vacuum.

Edit: well, I did say 'exist', but I guess it would be more accurate to say 'persist'.

Also, the atoms preventing evaporation thing is more or less the same as creating atmospheric pressure, so again, not a vacuum anymore.

Edited October 22, 2015 by The_Rocketeer

[Retread]

I wonder if the water-drop-in-freefall thing has ever been done in a vaccum. Would a glob of water released into space truly just vaporize? Or would a solid, frozen "skin" of ice form, allowing the water inside to remain liquid for a time?

[The_Rocketeer]

I wonder if the water-drop-in-freefall thing has ever been done in a vaccum. Would a glob of water released into space truly just vaporize? Or would a solid, frozen "skin" of ice form, allowing the water inside to remain liquid for a time?

Well, the ice-crust formation would mean that the water inside was no longer in a vacuum, since the crust would create a pressure membrane. From what I understand, this is how space scientists think there could be liquid oceans on Europa.