Wobbling Ship

[kolan4ik88]

My orbital ship is wobbling. Ship has 3 long modules. Sorry for bad English

There is no wobble when i attached first 2 parts. But when i tried to dock the ship started to wobble. I`ve disabled autostrut in one of clipping parts. The wobble gone. When i tried to dock 4 module the ship wobbled again. And i can`t stop it. Please help

[bewing]

Sorry, but this is a known bug in the physics, and nobody knows how to completely stop it. You can temporarily stop it by using timewarp. Sometimes that is enough to make it stop wobbling completely.

[kolan4ik88]

4 hours ago, bewing said:

Sorry, but this is a known bug in the physics, and nobody knows how to completely stop it. You can temporarily stop it by using timewarp. Sometimes that is enough to make it stop wobbling completely.

Time warp doesn`t stop it. Shame. I`ve spent 2 hours

Edited January 21, 2017 by kolan4ik88

[diomedea]

Time warp would stop it if you could warp just when forces between any two modules were null. Warp kills all relative velocities between parts, but if two parts are misaligned they will remain so, and exiting timewarp will again create physics forces meant to re-align the two parts.

With the Unity physics engine, parts are allowed some "freedom" but each time they move from where they are supposed to be (in relation to the next attached part) a force is created to bring the two parts towards the correct position.

Trouble like wobbling shows more when massive parts are attached through something smaller. In particular, through a couple of docking ports, as such ports don't even disperse energy, allowing movements to keep going for very long times. In the worse situations, using time warp at the wrong time with a long vessel already subject to such forces between parts, often the vessel breaks apart when exiting timewarp (as the forces recreated at the moment would even be greater than the maximum allowed).

I'm unsure about how to easily explain this mechanical phenomenon. You may consider two attached parts to be able to oscillate like if one is a pendulum in relation to the other. The more massive, and the farther away the center of mass of the two parts, and the less the reaction provided by the attachment (very little with docking ports), the longer the oscillation and more intense the forces can get at the max displacement. Like with all pendulums, there is alternation of potential and kinetic energy, the first when the two parts are the more displaced from the rest position, the second when the wobbling speed is largest. You may be able to think at each form of energy like it was flowing with time, like a wave. And if more modules were tied that way, a wave of energy could be "seen" to move across the whole structure, from one side to the other and then back. That's how such things work in reality, just like with a guitar cord.

What to do then to fix the problem? well, building so to avoid large massive parts being attached only by small ones. Struts help greatly to reinforce structures, though they also contribute to make forces, so could even worsen the issue if linked at wrong angles. While docking heavy modules, be extra careful to avoid misalignments (ports would still make the docking, but then the single resultant vessel would start wobbling because the physics engine has to cancel that misalignment.

[DerekL1963]

1 hour ago, diomedea said:

What to do then to fix the problem? well, building so to avoid large massive parts being attached only by small ones. Struts help greatly to reinforce structures, though they also contribute to make forces, so could even worsen the issue if linked at wrong angles. While docking heavy modules, be extra careful to avoid misalignments (ports would still make the docking, but then the single resultant vessel would start wobbling because the physics engine has to cancel that misalignment.

Installing Kerbal Joint Reinforcement may also help.

[bewing]

An alternative to DerekL1963's suggestion is to try the different autostrut modes on all the big parts. Some modes may work better for some ships than other modes -- which is why the devs gave us a choice.

[kolan4ik88]

48 minutes ago, bewing said:

An alternative to DerekL1963's suggestion is to try the different autostrut modes on all the big parts. Some modes may work better for some ships than other modes -- which is why the devs gave us a choice.

This doesn't work too. I've tried it

[Reactordrone]

Also make sure SAS is turned off and reaction wheels are disabled. Oscillations are frequently made worse by active SAS on a flexible structure.