How can I know the maximum slope my lander can land on without flipping?

[goldenpeach]

Like the title suggest, I would want to know the highest slope angle a lander can land on without flipping(and without using RSC/reaction wheel to make it stand still.

So, how do I calculate that?

Is there any mod that can help me do the calculation(even by saying some parameter I need to know)?

[Tex_NL]

Testing it in the VAB/SPH would be a lot easier than calculating.

Load your lander in the VAB/SPH.

Extend all landing legs.

Call up the Centre of Mass indicator.

Now slowly tilt your craft until the CoM indicator moves outside the landing legs. This angle is where your craft will tip over.

The rover on the left can handle a 45 degree bank. The one on the right can not and will roll over.

Edited June 3, 2014 by Tex_NL

[sal_vager]

Though I don't know how to calculate this it is possible to judge by eye.

Enable the center of mass indicator and see where the CoM of your lander (and just the lander) is in relation to your landing legs, you will want to keep that CoM inside the footprint of your craft.

Rotating your lander before you touch down so one leg is pointing down the slope will help a great deal, as with most 4 or 3 leg designs there's less support between the lander legs, the footprint is narrower at those points.

Keeping your CoM low will make things easier, don't forget to take fuel mass into account, it can greatly affect your CoM, also having your landing legs further out greatly increases your landers footprint.

Ninja'd!

[Pecan]

No mod I know of but the critical rule is that if a line drawn vertically from the CoM is within the area of the base it should stay up - the Leaning Tower of Pisa being the classic example, although it's always trying to fall over!

Display the CoM marker in the VAB/SPH and extend whatever landing-gear you have. Measure the angle between the CoM and the 'feet' - that's the angle you 'should' be able to land on. A lower CoM helps by making the angle wider, as does a wider base (of legs) for the same reason. This is the best explanation I could find with a quick search: http://www.angelfire.com/nc3/pweb/lessons/stable.htm

Double ninja'd - nice diagram Tex_NL :-)

LOL - and we all added the 'ninja' tag!

ETA: 'Fat Sally' (post #5 in the tutorial in my signature) is a small lander specifically designed to cope with slopes, and so illustrate the difference between that and a tall, thin one. In the illustration it is sat on a 30-degree slope (according to MJ) but I have, accidentally, landed it on 48-degrees without a problem while visiting a Mun arch.

Edited June 4, 2014 by Pecan

[Pondafarr]

You can eyeball it in the VAB. Enable the CoM cursor. Draw an imaginary line from the CoM to the outside edge of the narrowest footprint of your landing gear/wheels, like drawing a triangle. Now imagine that line is vertical (you can rotate the craft in the VAB to envision this more easily) This is the maximum tilt before you will topple over (assuming you are not moving, zero side motion)

Lateral motion will complicate things, but you *should* be ok if you keep your craft between vertical and your maximum tilt.

FYI, a wider base increases the maximum tilt your craft can accommodate, as well as keeping your CoM as low as you can (closer to the "ground")

Dang, got triple ninja'd

[Tex_NL]

I have ninja'd people before in the past but as far as I know never a triple.

And that diagram. It's not my own, I merely found it with some clever Google-Fu.

[michaelhester07]

Don't care about Ninjaing when answers need repeating!

Let the end points of each lander leg form the points of a polygon. Triangular is best. Your ship's center of mass cannot pass outside this polygon as projected on the ground or it will tip over.

Let two vectors:

->A = from the center of one of the edges of the leg polygon to your ship's center of mass

->B = from that same center to the point perpendicular to that edge

The 90 degrees - (angle between A and is the maximum slope you can land on. Since you can't get these positions exactly you'll have to eyeball it in the VAB. Make sure you eyeball along the edge of the leg "triangle" and not the points.

You can increase the footprint of this polygon (and thus the amount of slope you can land on) by attaching the lander legs to the ends of girders or Ibeams.

I should also note that there will be a maximum slope that you can land on regardless of leg footprint due to the friction between your lander's legs and the ground. This slope is shallower for the more gravity the thing you're landing on has. If your lander slides down the slope you land on you'll reenact a proper Kerbal landing (where everything blows up).

Edited June 3, 2014 by michaelhester07
fixed the triangle math

[goldenpeach]

Thank you for the answers!

I was going to use inertial momentum(trying to find it with KOS(I think it can do that).

I *think* it possible to use that to calculate the maximum slope but it's quite complex(furthermore, I don't know how to do that )

Also, thank for saying me how to make a better lander(in term of slope capacity);however, I was asking that because I recently discovered that my space shuttle I used for LKO mission(changing crew to my space station; although the plane can only transport one kerbal) or HKO(high kerbin orbit) missions(fixing geostationary sat when I deliberately forgot to deploy the solar panels).

(yes, I might have put too much fuel on that space plane.

I made some test and basic calculation and discovered that it have enough fuel to land anywhere on the mun: the only problem is that the plane is long and has (very) short landing legs(I put the bigs landing legs around the FL-T800 fuel tank).

TL;DR: thank you, the craft I use as a lander don't have can't cope with a decent slope but I don't care because it was never intended do land anywhere but the runway after being in space.

[EdFred]

Keep in mind that the above posts are only true when you have no movement. When you touch down, there will always be some movement - especially with slopes. If you cut your engines when the higher legs touch, there will be some rotation as the lower legs settle - and this assumes you have 0 horizontal movement when touching down. And if you keep a little bit of thrust in as you set down the lower legs, that thrust will translate into horizontal movement - and then rotational as well. So what looks workable in the VAB my not be workable in action.

Calculating it isn't that hard if you know your horizontal vector, COM, and frictional coefficient of the surface.

[SpeedDaemon]

As EdFred said, being stable on a slope, and actually getting landed on one aren't the same thing. Landing will generate some angular momentum, which can tip you over even if your CoM is inside your footprint.

You can try designing your lander with slopes in mind, so that you can raise some of the legs on the uphill side and be a little more level. Or use Infernal Robotics hinges to angle your landing legs so your engine is still thrusting straight down as you land.

[SpenSpaceCorp]

Though I don't know how to calculate this it is possible to judge by eye.

A way to "judge by eye" would be to associate each small rotation (each shift click) with a certain degree. (I don't know it, i'd have to calculate it). But, for example, if each SHIFT + wsadqe key rotated it by 10 degrees, add those up with each rotation until desired.

EDIT:

I tested it, and it takes 72 "shift clicks" to rotate an object 360 degrees. So, 360/72 = 5, meaning each shift click rotation is equal to 5 degrees. So, to calculate the slope it can handle, simply count how many shift click rotations it takes you to acheive the desired angle, and multiply that by 5. That gives you your slope.

Hope that helps!

Edited June 3, 2014 by SpenSpaceCorp

[problemecium]

One thing I've learned from my zillions of landings: no lander can handle any slope more than one degree. No matter how ridiculously wide and pancakey you make it or how carefully you land, KSP will wrench it away from vertical and smash it.

[MarvinKitFox]

One thing I've learned from my zillions of landings: no lander can handle any slope more than one degree. No matter how ridiculously wide and pancakey you make it or how carefully you land, KSP will wrench it away from vertical and smash it.

o rilly?

wow, i must be dumb then, I didnt know i was breaking the rules by landing on 62* slope....

My lander is just 14 times as wide as the height of its center of mass

disclaimer: *plenty* rcs used to achieve landed state, from first contact. But not needed to sustain the landing

It can actually handle a slope of 85*, assuming I can get the lower leg wedged into a crack of some sort. Otherwise it becomes slide city.

Edited June 4, 2014 by MarvinKitFox