Why are rovers so hard?

[Ol’ Musky Boi]

As an addition to my Mun base I attempted to design a fuel transportation  and long range exploration rover. I tested all my designs with hacked gravity to simulate a Munar environment, and all of my designs, regardless of centre of mass or wheel base would flip over when they turned, I had no reaction wheels on board to prevent the WASD keys from changing the attitude. Was this a mistake? Should I have SAS enabled? Please send help 

[KerikBalm]

Pics would help.... 

The key to any rover is a low CoM and wide wheel base. The lower the gravity, the more important that this is (or in 1/3 gravity, your rate of turn for a given velocity must be increased by 3x)

[G'th]

^ This is the basics of it.

But another thing to consider is changing the settings on your wheels. By default the stock wheels are not really configured for the low gravity on the Mun, nor even on Kerbin for that matter (unless you have a sufficiently heavy rover). 

Try playing with the traction tweakables to make them less powerful so you don't get too much speed too fast.

How you control the rover is also important. Either make wide, gentle turns or slow yourself (by pressing S to go reverse. Brakes even when you're rover is perfect tend to flip you) and then turn. Should also control your speed. At a maximum you should only be going 20 m/s. And thats on flat terrain for a long distance. In general you want to keep it around 10m/s.

[MiniMatt]

Reaction wheels + SAS modes are another thing to try playing with - the default setting, as you note can cause the A/D keys to roll, but you can click through SAS modes and one of them (think "Pilot", can't remember) helps to maintain some stability without inducing roll or pitch.

edit: some other tips - disable steering on the rear wheels as a way of restricting turning, and setting much lower braking force on the front wheels than the rear to ensure your rover tends to lock up and drag under braking rather than flip. And yeah, much lower speed - unfortunately to the point where roving any distance becomes more a chore than a joy, but yeah, 10m/s is ~22mph and already double that tried on the Moon.

Edited April 16, 2018 by MiniMatt

[TheFlyingKerman]

2 hours ago, Ol’ Musky Boi said:

I had no reaction wheels on board to prevent the WASD keys from changing the attitude.

You mean you use the WSAD keys to steer the rover? Map those to other keys to separate steering and rotation.

[Gargamel]

1 hour ago, G'th said:

Brakes even when you're rover is perfect tend to flip you

This can be helped by redistributing the braking forces.  If your rover tends to nose wheely when braking, reduce the braking force in the front, and increase it in the back.   I usually prefer to run with at least 20/80 Front/Rear braking.    Also, I've found that turning off steering in the rear wheels helps increase your turn radius, reducing flipping.    But if you have long trains of wheels, you almost require rear steering, so this can become moot. 

[blakemw]

Another factor is center of mass, while not perfectly relevant to KSP rovers, it's instructive to watch this really short video about center of mass: 

 

 

If your rover is nose-heavy it'll basically want to keep going nose-first, this means it tends to understeer (you try to steer, and it wants to keep going in the same direction as its already going)

But if your rover is tail-heavy, it'll basically want to go tail-first, this means that it'll take any excuse (such as loss of traction) to try and spin around and go backwards, which will usually result in flipping as the wheels on one side dig in and try to resist the rotation. If it's otherwise stable it'll tend to oversteer (when you start steering, it'll be over-enthusiastic about turning).

Obviously being mildly nose-heavy is a big stability advantage for a rover in a low-friction environment like a world with low gravity (though being too nose-heavy might encourage doing a nose-dive style of flip).

 

Moving away from the real world, in KSP you can tweak numerous properties of wheels (if Advanced Tweakables is enabled). The most useful for stability is "friction control" which determines how much wheels "bite". Leaving friction control at auto is a bad idea! Auto is like "stupid" or something. Setting friction control to 0 makes wheels frictionless which is great for sliding around and not flipping, but you can't accelerate, brake or steer... Setting friction control to 5 will make the wheels toss the rover around, any loss of traction will cause severe forces on the rover. Usually, the best handling is found with a friction control of 0.5-0.8. Happily you can even adjust friction control on the fly, the main thing you lose with a low friction control is braking power (it's not such a problem in terms of acceleration), so if you've set friction control to a low value for improved stability, you can just crank it up for improved braking, like to make the rover stay still on a slope. It also tends to be helpful to have a lower friction control on front wheels than rear wheels, because the front wheels are more prone to cause flipping.

Edited April 16, 2018 by blakemw

[Gargamel]

14 minutes ago, blakemw said:

t's instructive to watch this really short video about center of mass: 

Not only will this help you in game, but it's a very pertinent life skill.  The vast majority of people will end up loading a moving truck or trailer at some time in their life, and it's good to understand how to load one.  As a medic, I have responded to quite a number of trailers that got loose due to poor loading. 

[LordFerret]

We can take this a step further...

I had similar problems with my Mun rover. I made all of the above suggested adjustment - brakes, traction, steering enabled/disabled, etc. Still, I found myself with many a time where I'd be flipping my rover. Reducing your speed prior to attempting to make a turn is a big help, but there are moments when this has no bearing or help what-so-ever, like when your rover makes a hop (takes air) over a bump or crater rim. When that happens, the slightest change of direction due to the landing can end your ride quick.

My solution was to carry some liquid fuel and place LV-1R Spider engines at strategic points on my rover... fore / aft / port / starboard... and map the engine toggle to action keys (in my case: 5, 6, 7, and 8 respectively). With thrust pre-set prior to starting off on my cruise, if I did find myself in the midst of a flip, I could tap in some thrust from an opposing engine to prevent the flip. Didn't always work, but it saved me more times than not. It also came in handy when trying to ascend / descend a steep crater wall, adding a little extra 'oomph'.

If you look at the image below, you'll see how I placed the Spiders, up top on the Science Jr...

 

Good luck with your venture!
 

[Ixamus]

I have spent lot of time rovering around Mun and Duna so I think that there are things I can say about it. Successful rover mission (while I'm driving) rely on lots of f5 and f9. I recommend you to do so, since even the best vehicles can sometimes flip and blow up. What I do not recommend is to limit yourself to driving only 10 or 15 m/s since that is boring and getting anywhere takes forever. All rover missions are quite lengthy but I see no reason for them to be excessively so.

In addition to saves and load I believe that the key is wide wheelbase and ability switch reaction wheels on and off with command group. While you are using your wheels to accelerate or turn you should have your reaction wheels off, but otherwise they should be used to keep your rover straight and not flipping. Personally I use excessive amounts of sas units to overcome other forces and force my rover not flip, should there be close call.

I also think that bigger rovers are better at this. You can drive lot faster "safely" since they are very hard to flip. I embedded an image of my latest rover/mobile base design below. I can drive relatively "safe" on hilly terrain 50 m/s. I do admit that it's somewhat difficult and resource intensive to deliver anywhere.

Driving rovers in KSP is also skill to learn. I have managed to reduce my crashes and quick loads quite a lot simply by becoming a better driver and learning to find the safest path across the terrain.

[storm6436]

I guess I'm the only one who includes attitude correction devices (DMagic's magnetic science booms) on my roving type vehicles for when I inevitably roll it. 

 

 Just activate SAS, extend the correct boom, and pitch/roll correctly till you're upright. 

[Azimech]

What @blakemw said and this is absolutely 100% true and the best way to prevent flipping: set Automatic Friction Control to "override". For low grav worlds I might set the friction to as low as 0.1 or 0.3.

This automatic system seems like some kind of weird "AI" that tries to understand what the player wants. In the meantime the player expects a certain behaviour but gets ridiculous results.

 

[SchwinnTropius]

I like the option of SAS on any rover I drive, so to avoid unwanted movements while driving, I set the reaction wheels to SAS-only.

[Vanamonde]

This sharing of craft (for such it has turned into) has been moved to the craft sharing subforum. 

[FleshJeb]

In addition to the other techniques mentioned here, I build my long-range rovers with roll cages and skid-plates. Nothing fragile can touch the ground until a whole lot of steel gets ripped off. In addition, I usually add enough reaction wheels and Vernors that they can self-recover on Kerbin. (I find about 4kN/ton works well).

Just for fun, I spent 30 minutes building this example rover and took it to the Mun. It survived multiple 35 m/s uncontrolled rollovers with minor loss of parts. Fully-loaded, it weighs 65 tons. It can certainly be improved, as it's just a concept demonstration.

If you want to have fun roving, armor and redundancy are key.

Edited April 17, 2018 by FleshJeb

[Lego_Prodigy]

I have found that if you turn too fast, thats a HUGE cause of flipping, so when turning keep it gentle, and under about 10 m/s for good measure.

[FinalFan]

New player here.  As it happens, I recently created my first real rover, not counting my "For Science!" KSC exploration abomination, in order to fulfill Mun surface contracts I accepted without a real concept of how to complete them. 

I quickly learned that the two main choices (aside from hopping to all the places in a lander) are to build a very low slung vehicle and drive it conservatively enough that you just don't flip over, or build a vehicle that can reliably recover from inevitable hilariously long-lived wipeouts at top speed.  A compromise solution exists with the "RCS to stop flips in progress" as with LordFerret. 

I went with the Suvivability option: 
[edit:  TinyPic is dead; long live Flickr.  Original link for insanity posterity:  http://i65.tinypic.com/289kjg2.jpg ]

I'm really pleased with the end result.  It cruises from 20 to 30 m/s, and is surprisingly stable (I was able to recover from tilts I thought were sure wipeouts).  And when it does flip over, after bouncing around for a hilariously long time on its many wheels, it tends to land upright!  The topside LT-2s work like a charm when it lands on its head.  The LT-1s on the side aren't as reliable in the rare event that it ends up on its side (I had to deliberately try to come to rest this way in my test run) so I may tweak the design.  But I'm pleasantly surprised at how well this worked out.  I wanted it to be great at surviving wipeouts, which it is, but its actual driving performance is everything I could have hoped for—way better than I was expecting! 

If I had to name the biggest flaw to this design, it's that when it does wipe out it takes forever to stop bouncing, at least on the Mun. 

Edited September 22, 2019 by FinalFan
TinyPic is dead; long live Flickr.

[Ol’ Musky Boi]

Thanks for the advice, I’ve got no WiFi right now (I’m writing this in a Thai restaurant) so I can’t show any photos, but I’ve decided ISRU suborbital “hoppers” are the way to go. They’re quicker and easier, with an infinite range. I call em’ my ballistic Imps.  

[justmeman117]

There’s a ton of stuff you can do, I already see a bunch of people talking about tweaking wheel traction and wheel bases.

 

Personally, I set the rear wheels to toggle on an action group. If you turn off rear wheel steering at high speeds, you get more stable turns at the expense of turn radius... Who needs to make sharp turns at high speed anyway?

 

And if you want to get cheaty about it, the COG of jet engines are outside the physical dimensions of the part... This means you can put a bunch of them on a rover facing downwards, and move the rover’s COG below the ground. Doing this makes the rover rotate into the turn instead of away from it. It also allows it to scale 90 degree inclines, which is pretty cool.