Is this a bug? Rovers get mired and sloweed in ground at craters' edges.

[Dunbaratu]

Have other people seen this effect? I'm driving a rover up out of a Mun crater onto the rim, and when I get to the top and move out onto the first flat polygon atop the rim, it behaves like it's made out of slow muck or sand. The rover gets slowed down on that top polygon a LOT such that I can only make about 0.3 m/s trying to drive it at maximum speed. I have to creep slowly off that terrain polygon onto the next one before the wheels finally break free and it starts driving normally again. I thought it was just a fluke the first time but I've done enough rover driving now to see that it tends to happen a lot on the edges of lots of different craters.

   This polygon bogs down rover.
          |
          |
          |
        .----.

        _____
crater /     \__
rim   /         \__
     /             \__________
    /  \        |        
   /    \       |     /
  /      \      |    /
 /     These polygons act correctly.
/                            

Edited October 2, 2013 by Steven Mading

[Specialist290]

I think you're running into the same problem I've run into on the Mun and have heard other people talking about: Sometimes, the terrain graphics don't quite match the actual surface polygons. Sometimes, I've noticed that my wheels don't exactly "catch" on the surface, so (since the rover design I've been using lately has a ludicrous amount of torque from reaction wheels) I'll occasionally "tweak" the forward end down just a tad, which usually helps.

[Geschosskopf]

There are 2 things that can make rovers act strange atop the rims of craters:

1. SAS Needs Resetting

As you climb the crater rim, your rover spends a long time at a fairly steep nose-up attitude. If the rover has a probe core and/or reaction wheel unit AND you have SAS turned on, you have great traction during the climb. This is because SAS tries to keep the rover at the attitude it was in when you turned SAS on. The angle SAS wants to keep changes over time but it's always going to lag a bit behind the increasing slope. Thus, as the slope gets steeper, SAS is always acting in the opposite direction, thereby increasing your traction and both your acceleration and braking power.

Then you get to the top of the rim and the ground more or less levels off. On the typical rover, the torque of a single probe core is enough to counter gravity on Mun, so now SAS is trying to keep the wheels off the ground, more like at the angle they were just at when climbing the rim. It thus often happens that each time the slope decreases noticeably as you're going uphill, you end up with only 1 or 2 wheels touching the ground, the rest held just above the ground by SAS. Hence, no traction and so no acceleration or ability to brake or even steer. The result is "bogging down." To solve this problem, turn SAS off for a couple of seconds, allowing all the wheels to make good contact with the ground, the turn SAS back on. Voila, you can now accelerate, decelerate, and turn again.

2. The Geschosskopf Effect

Where the rims of overlapping craters intersect, there's a small force exerted on wheeled objects (only, nothing else) inwards along the line connecting the intersection points of the crater rims. This force isn't very strong (brakes can resist it) and is only really noticeable on the outside of the rim, so the force acts against gravity and makes the rover roll uphill. But if you're at such a place and are trying to move slowly downhill, this force can make you think you're bogged down.

[Dunbaratu]

2. The Geschosskopf Effect

Where the rims of overlapping craters intersect, there's a small force exerted on wheeled objects (only, nothing else) inwards along the line connecting the intersection points of the crater rims. This force isn't very strong (brakes can resist it) and is only really noticeable on the outside of the rim, so the force acts against gravity and makes the rover roll uphill. But if you're at such a place and are trying to move slowly downhill, this force can make you think you're bogged down.

That sounds like what's happening.

[Galane]

I put the stock rover on the Mun, where it's stuck in a large crater inside the really huge, dark crater. I tried several times to get out onto the relatively flat terrain amongst the craters but ended up flipping backwards at the top of the rim instead of the front wheels going over.

Once I nearly managed to make it into a smaller, intersecting crater that was further down the slope but some rather coarse geometry jammed things up and it ended up tumbling back. It's a very tough rover. Nothing broke until the last time.

Then I decided to go up the high side because there's a small crescent of intersecting crater whose upper lip has a shallow transition to the "between craters" landscape. I *almost* made it before the rover flipped back. That was one loooooong tumble during which everything but the center bottom plate, the two middle wheels, the probe body and two batteries got ripped off. The rover was still drivable! (Until the batteries died.) So I Mun-schussed down the the lowest point of the crater before hitting F9. Also got in some practice fiddling with control to keep it balanced on two wheels.

Some day I'll try going out the lower side, into the next crater to see if I can get over its lip.