Kerbal Space Program

Update: Still happens in 1.4.5

The problem is relevant also to LT-05, LT-1, and LT-2 legs as well as LY-10 and LY-35 landing gear - basically all original KSP landing parts I've checked. Best way to test: set damper to minimum value, 0.05. While the object could swing, this should die out slowly. Instead, the energy grows rapidly. My test craft starts to jump and after two or three jumps legs get destroyed.

Of course 0.05 damper value isn't the one that should be widely used but it shows that energy that should dissipate cumulates rapidly and catastrophically. This is physics (simulation) flaw.

While these parts worked quite well previously, there is a regression. I have a lander like the example craft on the Minmus, "standing" on 3 LT-1. When landed (or when legs are retracted and then extended again) the ship swing for quite long time despite dampers ans springs are set to default 1.0. When swinging dies out, the ship stands tilted like the springs were not strong enough on Minmus while they keep the weight well on Kerbin (where dampers set to 2.0 deal with swinging well but set to 1.0 appear to keep the energy constant).

Also LT-05 seem to support craft's weight even better on Kerbin than on Minmus. It's strange taking int account that Minmus' gravity should barely compress the spring by a tiny amount.

The craft has mounted 3 types of legs, attached to actions 1, 2, and 3. On either set of legs it starts to jump.

After playing a bit more with base on Minmus I concluded that with legs physics something went really wrong. Found that LT-1 with damper and spring set to 1.0 doesn't work well, I tried to send another part of the base equipped with overkill 2.0/2.0 LT-2 legs. Didn't help. The ship is still unstable. Once landed it was OK, but too far from a base so I flew a bit closer and then one of the legs seemed weaker and the ship would fall to the side if reaction wells wouldn't keep it straight. Got it up and sat down again so it stabilized. Connected with KAS pipe. Ships connected with these links don't swing but this ship didn't stand straight so I unconnected to release tensions... Then it started to swing and suddenly was thrown several hundred meters up into the sky. Certainly LT-2 can absorb and release a lot of energy. Energy basically from nowhere... Maybe it has dark energy converter inside?

Well, after few falls, explosions and insane jumps (legs bounced again and again from the ground) the ship laid on its side rolling left and right. When rolled onto one of it legs some mysterious force was compressing leg's spring (acting sideways on it). The second leg worked similarly but additionally the ship had been rotated on the ground by some dark energy that must have been leaked from damaged converter.

Leg basics are quite simple - the spring should generate force proportional to its compression while the damper should generate force proportional to speed of compression/decompression. These forces should act along the leg while for perpendicular forces the leg should appear stiff. Currently it looks like the solution was rather opposite... And on the Mimnus, where the gravity is so small the slow compressing of the spring proves really low force. Certainly lower than on Kerbin where the same mass acts with much more force still being held up by the same legs. While the player cannot change leg parameters in flight (reasonable - how to change the spring?) why do they fluctuate on their own?

Spring's and damper's strength are unitless values. Why? If one knew that the spring will generate 10kN per m of compression while the leg can contract 0.5m this could be calculated which legs, how much of them with which spring should be used for a ship to land in given range of gravity. Having damper's strength (Ns/m) and leg's endurance (N) one could calculate maximum grounding speed. While earlier legs worked quite well set 1.0/1.0, this wasn't so important. Now they generally don't work well.

This must be fixed.

• AviationLights
• Chatterer
• CommunityCategoryKit
• CommunityResourcePack
• EasyVesselSwitch
• FlagPack
• KAS
• KIS
• PlanetaryBaseInc
• PolishFlagPack
• SquadExpansion
• SurfaceLights
• TriggerTech

Have same issue with game in Linux with no mods installed. I've tried to disable "Ease in gravity" and "Physics delta per frame" to on/off and from 0.03/0.04 to 0.12 with no luck (it may just slightly change amplitude or number of cycles to explosions).

Unplayable planes having LY-01/LY-05:

0) Of course, oscillating craft is hard to control on take off
1) May oscillate until craft rips apart or hits runway hard shortly after spawning
2) It may end up being in uncontrollable jumping motion to the side when craft is impossible to recover since it is "moving"

Attached Wobble-1 is craft file with absolute minimum to get this triggered.

What is observed: heavier craft is, bigger amplitude is. You need about 3t to make this can on 4 gears to oscillate very noticeable. With second FL-T400 and 5.2t it starts to jump into air. With third FL-T400 (craft Wobble-2) it starts moving on runway and you may not recover it. With 2 more FL-T400 and mass about 12t it will explode after second oscillation.

It was flawless in 1.4.3 (nothing of above happens).

Happens on MacOS as well. Sometimes gear/landing strut configurations that function as expected on Kerbin will misbehave in low-gravity environments (i.e., Minmus and Gilly).

The LY-01 should be much more stable in 1.5.0

Version 1.5 gives a useful workaround that reduces the frustration from this bug immensely.

Enabling the setting 'Advanced Tweakables' shows a button Spring/Damper {auto, overrride} and if we set it to override, we can adjust the damping as needed with the craft in operation. Previously, the adjustments were available only during construction.

If I were to formally test, though, using the example craft given in the report:
bouncy_landing_legs still bounces (override cures)
DAMPER_EXAMPLE(medium legs) bounces (override cures)
wobble-1 bouncing damps
wobble-2 very slowly damps

Improvements have been made up to 1.7 with the landing gear. Setting this bug to RTT to see if the original issue is now fixed.

Results with the example craft are the same in version 1.7.0 as reported for version 1.5.1

The PC version 1.8.1 has resolved this, presumably from its update to newer Unity engine.
The example craft, with default settings, now damp nicely.
(Possibly that means the console version gets the resolution when a KSP with the new Unity engine reaches consoles.)

1) The default springs on the lightest landing gear are set for a very light craft, so 'bouncy landing legs.craft' bottoms-out the landing gear, but no longer bounces. Increasing the spring strength to 2 makes them more appropriate for this aircraft, and they still damp out any bouncing.

2) The spring/damper settings now persist, so toggling the right-click option to 'auto' merely hides the sliders, leaving the effect as it was when sliders were shown. That means, the 'DAMPER_EXMPLE.craft' retains its very low damping that it was saved with. Returning the damping sliders to their default, or adding fresh landing legs from the VAB, results in quickly damped bouncing.