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Settings for lander legs


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It's black magic. The stronger your springs, the bouncier they are. The stronger your damper, the less bouncy they are. But if you get the values just wrong, you can set up a feedback resonance, and blooey!

So it's best just to take your example lander to the proper destination multiple times, and try various values.

 

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Hmmmm. Well, I'm doing a little testing to see how it works in 1.4 -- and it seems to be working the way it theoretically should. I'm using the Hack Gravity cheat to try to make things work wrong/right on the kerbin launchpad. What's the mass of one of your typical landers when they are on the Mun? You know you can get that number while you are in Map mode?

There is an autotuning thing for the springs. Suddenly I'm wondering if that's the problem. That the springs are getting set for Kerbin gravity at launch, and then are not getting reset at the destination? Hmmmm.

Are you doing this Mun launch/landing all in one go? No focus switches away from the craft during the flight?

In any case, I'm having pretty good luck in my testing just by boosting the dampers to 1.5.

 

Edited by bewing
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17 hours ago, Jestersage said:

But isn't there a ballpark? Like 1,1 is for Kerbin, so Mun maybe 1/6 or 1/4 that kind, etc?

Not really, it's a two-variable equation - the gravity of the planet, and the mass of the craft.

A screenshot would really help show what you're dealing with.  You might just be overloading them.

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On 5/15/2018 at 3:07 PM, Jestersage said:

Can someone provide a tutorial for the settings of lander legs, namely, how to set them so that they function well for landing? All my mun lander feel like bouncy castles (1.4.3 btw)

There's no one setting, because how much spring and damper you need is going to depend not just on local gravity conditions but also on the mass of your ship.

  • Having a spring setting that's too low has the risk of reaching the "end of travel" (i.e. trying to compress too far) when landing, if your landing's not gentle enough.
  • Having a spring setting that's too low can also mean that your ship's too prone to wobble around when on the ground (e.g. leaning too far over, if you're landed on a slope), if the springs in the legs aren't stiff enough to support the vehicle's weight.
  • Having a damper setting that's too low means that things bounce and oscillate.

I generally like to set damper as being somewhat higher than springs.  e.g. I might raise damper to 1.5 and springs to 1.2 or 1.3, for example.  My experience has been that if damper > springs, bouncing generally isn't a thing.

If you're having bouncy-castle problems, my suggestion would be to crank up the damper a lot (that will reduce the bouncing), and raise the springs somewhat, but not as high as the damping.

^ The above advice is based on no formal testing whatsoever, it's just what I usually do and it usually seems to work out pretty well for me.

 

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16 hours ago, bewing said:

In any case, I'm having pretty good luck in my testing just by boosting the dampers to 1.5.

I'm still in 1.3.1 - I discovered that the higher the damper, the more they like to launch into the air on load. The spring setting doesn't seem to cause this problem. I started setting all mine to 1.0/0.5. They bounce a lot but it dies down after a bit.

Edited by FleshJeb
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So the mass of my lander is at 15.7T; targeting mun; from a AP-PE orbit of 50k-6k, I start to land at PE (basically tutorial landing). Still adjusting the legs... but still get Good old bouncy castle.

Edited by Jestersage
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9 hours ago, Jestersage said:

So the mass of my lander is at 15.7T; targeting mun; from a AP-PE orbit of 50k-6k, I start to land at PE (basically tutorial landing). Still adjusting the legs... but still get Good old bouncy castle.

Let me try my crystal ball.

Omens, portents...  Death.

I see death.

Not yours.  Just the apple you packed in your lunch.  I think it's your lunch, but might be anyone's.

Sorry, without a screenshot I can't really tell what's wrong with your lander legs.

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29 minutes ago, Corona688 said:

Sorry, without a screenshot I can't really tell what's wrong with your lander legs.

Okay, I don't get it -- why do you need screenshot? Legs mount radial, 4 way symetery ala Apollo, deploy, point down, the landing side clear the vessel -- done. Change settings in VAB as needed.

 

I mean, apollo's leg is the same as altair, just bigger with different settings account for different mass...

Edited by Jestersage
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31 minutes ago, Jestersage said:

Okay, I don't get it -- why do you need screenshot? Legs mount radial, 4 way symetery ala Apollo, deploy, point down, the landing side clear the vessel -- done. Change settings in VAB as needed.

For one thing, I can't see if you're using tiny matchstick legs on a 15 ton lander.

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Okay, I finally found out why I was bouncing around: My CoM was too high.

The craft in question is this one: HZ4zi6W.png

So what I did is to swap the Adapter Fuel tank with another 1.8m fuel tank (440 if I am not mistaken). Works like a charm: 8J5Yn7X.png

And as everyone guess... yes, it's a Lunar Gemini replica.

 

Edited by Jestersage
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3 hours ago, Jestersage said:

My CoM was too high.

And the footprint too narrow.  Plop those legs on the bottom of that tank, and it will both lower your CoM and increase the size of the footprint.   The legs should reach the ground without the engine hitting.

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6 hours ago, Gargamel said:

Plop those legs on the bottom of that tank, and it will both lower your CoM and increase the size of the footprint.   The legs should reach the ground without the engine hitting.

They are on the bottom of the tank... Just not on the bottom and side of the tank in order to put them inside the engine shourd.

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