Ground Vehicle Death Shimmy

[Zosma Procyon]

Does anyone know how to stop ground vehicles from shimmying until they either burst their tires or blow apart? I've been trying to get this mobile base design to work without the death shimmy for a week. Each time when loaded onto the launch pad, it either shimmies until the tires burst, or does what this attempt did and spins in a circle until I give up and revert back to the assembly bay. I have about a dozen mobile bases around the Kerbin system, so I know its possible to defeat the shimmy, but I can't get this one to work.

In this mobile base, all of the SAS systems and reaction wheels are disabled; so that definitely isn't the problem. If I got it to work, the pontoons would have wheels alternation outside/inside all the way down them. I have tried autostructing everything, autostructing nothing but the wheels which do it automatically, attaching the pontoons to the science labs, attaching them to girders hidden inside the science labs...honestly I still have a few ideas to try, but by now I'm confident that they won't work either.

I'm still using 1.4.4 and MH 1.3. I tried to update and got a bunch of errors including Unity errors and possibly every spacecraft I have not being loaded because of nonexistent parts. My mods are the most recent versions of mechjeb and kerbal alarm clock. By the time anyone reads this I will have deleted the failed craft pictured in this post and be working on a nearly identical attempt.

[mystifeid]

21 minutes ago, Zosma Procyon said:

By the time anyone reads this I will have deleted the failed craft pictured in this post and be working on a nearly identical attempt.

That's a pity because posting the craft file or save file somewhere is probably the best way of receiving timely help. We're just guessing otherwise.

[bewing]

Generally they shimmy because you've overloaded the wheels. The devs have been doing some experimentation to reduce shimmy, but there are no guarantees that the experimentation will go anywhere.

And yes, 1.4.5 did include some of that experimentation, so trying again on doing that upgrade may help you out. Nobody is saying that anything is "fixed" though.

Edited August 13, 2018 by bewing

[Zosma Procyon]

9 minutes ago, mystifeid said:

That's a pity because posting the craft file or save file somewhere is probably the best way of receiving timely help. We're just guessing otherwise.

I'll try to post the next failed attempt. I don't know how to do that, btw.

[bewing]

A craft file is just a text file. Just go to any cloudy file hoster. KerbalX. Dropbox. Google Drive. Even pastebin works just fine.

Copy & paste or upload the file, set any necessary permission settings, & post the link here.

[mystifeid]

45 minutes ago, Zosma Procyon said:

I'll try to post the next failed attempt. I don't know how to do that, btw.

The craft file will be in [game directory]\saves\[name of game]\ships\VAB\

Here is another example I've noticed lately. Lightweight - hard to call it overloaded yet it jumps around on the launchpad until a tire blows (rear left in second screenshot). Even with the fuel tank empty it starts jumping around when I start driving it around KSC.

But the wheels have had both spring and damper settings increased to 2.

Strange because the 16 wheel rover I've done most of my cn's with has all wheels with springs/dampers set to 2/2

and the 16 wheeler (11.648 tons of it) still behaves normally at KSC

Edited August 13, 2018 by mystifeid

[Zosma Procyon]

As mentioned in my last post, I have been trying to get this mobile base to wok for about a week. Here is a link to the google drive stored part file.

https://drive.google.com/file/d/1nsRq8QnZwdtJJYQtrVZCtBCpCMiiokcD/view?usp=sharing

Someone mentioned that the shimmy happens when wheels are overloaded. I don't think that's the cause, because the shimmy doesn't start happening until a certain number of pairs of wheels are attached, as illustrated by these screenshots.

Just 4 wheels, no shimmy.

8 wheels, no shimmy.

12 wheels, first sets of interior wheels fitted, no shimmy

16 wheels, shimmy present. And every iteration after this shimmied. The version I've posted in the link above slid sideways and would have fallen off if I hadn't paused.

Here are some construction notes. To hold the pontoons together, there are midsized docking ports tucked away in them. This is how I tricked the game into allowing two points of connection on the pontoons. Two docked docking ports per pontoon, which are autostructed to the root part, which is the capsule. Also, part clipping is of course turned on.

I haven't updated to 1.4.5 because when I tried yesterday, I got a bunch of errors I haven't seen before, including at least one Unity error which tried to open a Unity webpage but couldn't connect. And the game said that pretty much all of my spacecraft couldn't be loaded because of parts that no long exist. So I don't think the Mac releases of 1.4.5 and 1.4 are ready yet. In fact the MH update was listed as 1.3.1.

KSP Version 1.4.4, Making History version 1.3, most recent versions of MechJeb and Kerbal Alarm Clock.

[bewing]

20 minutes ago, Zosma Procyon said:

I haven't updated to 1.4.5 because when I tried yesterday, I got a bunch of errors I haven't seen before, including at least one Unity error which tried to open a Unity webpage but couldn't connect. And the game said that pretty much all of my spacecraft couldn't be loaded because of parts that no long exist. So I don't think the Mac releases of 1.4.5 and 1.4 are ready yet. In fact the MH update was listed as 1.3.1.

Did you get your update from steam, from the store, or from GoG?

 

[Zosma Procyon]

7 minutes ago, bewing said:

Did you get your update from steam, from the store, or from GoG?

 

The store.

[mystifeid]

So I tried modifying the first rover to be more like the second although still with only 8 wheels and surprise, surprise, I can do what I like with the springs / dampers (2/2) and it still drives normally around KSC. Go figure.

Edited August 13, 2018 by mystifeid

[klesh]

Its weird that they have resort to experimenting years after releasing the game.  Like, the wheels keep breaking and they fix them, then they break again.  Whats going on?  How come other Unity games don't have such atrocious wheel behaviours?

Edited August 13, 2018 by klesh

[bewing]

49 minutes ago, klesh said:

Its weird that they have resort to experimenting years after releasing the game.  Like, the wheels keep breaking and they fix them, then they break again.  Whats going on?  How come other Unity games don't have such atrocious wheel behaviours?

Because KSP is based on the (closed source) Unity engine, and Unity is based on the (closed source) PhysX physics engine, and the PhysX physics engine has a bug in its spring force equation. And Nvidia isn't fixing it. And if you check the other Unity games that use wheels and suspensions -- they do have atrocious wheel behaviors. The big difference is that their vehicles are pre-constructed and tuned to minimize the awfulness. But since KSP lets you build your own, there is no tuning possible.

So the KSP devs have to create workarounds for a bug that's deep within a library that they can't touch directly.

Edited August 13, 2018 by bewing

[mystifeid]

So it's probably not necessary to start a new thread for each reply.

Anyway, you had the dampers for every wheel set to 2. When this was reduced to 1 - no shimmy. And the highest setting that I found I could use for the dampers with no resulting shimmy was 1.4

The design has real problems going over bumps with a lot of weight being put on a couple of wheels. You can expect blowouts. I had more success when I removed them all and attached 24 wheels as near as I could in lines of 4. But It was still advisable to move over bumps carefully.

Without ever leaving or falling off the launchpad this is what happens if I leave the dampers at the original setting of 2.

Edited August 13, 2018 by mystifeid

[klesh]

Are the other games that use Unity and PhysX that have these same kinds of issues?

[bewing]

Similar, yes.

[Snark]

Merged threads.  No need to have multiple threads for one question. 

[Zosma Procyon]

14 hours ago, mystifeid said:

So it's probably not necessary to start a new thread for each reply.

Anyway, you had the dampers for every wheel set to 2. When this was reduced to 1 - no shimmy. And the highest setting that I found I could use for the dampers with no resulting shimmy was 1.4

The design has real problems going over bumps with a lot of weight being put on a couple of wheels. You can expect blowouts. I had more success when I removed them all and attached 24 wheels as near as I could in lines of 4. But It was still advisable to move over bumps carefully.

Without ever leaving or falling off the launchpad this is what happens if I leave the dampers at the original setting of 2.

Thanks. It won't look as cool, but I'll give it a go. I had the dampers turned up because of bouncing on landing. A few of my early attempts landed too hard, bounced, and flipped over.

[Zosma Procyon]

16 hours ago, mystifeid said:

So it's probably not necessary to start a new thread for each reply.

Anyway, you had the dampers for every wheel set to 2. When this was reduced to 1 - no shimmy. And the highest setting that I found I could use for the dampers with no resulting shimmy was 1.4

The design has real problems going over bumps with a lot of weight being put on a couple of wheels. You can expect blowouts. I had more success when I removed them all and attached 24 wheels as near as I could in lines of 4. But It was still advisable to move over bumps carefully.

Without ever leaving or falling off the launchpad this is what happens if I leave the dampers at the original setting of 2.

It worked. Thanks for the help. Now I have to kit it out for its flight to Ike.

[Zosma Procyon]

This is more or less the version that will be launched to Ike in about 200 days.

[XtraChrisP]

Holy geez!  How the hell you plan on getting that up to orbit?!?

[bewing]

MOar Boosters, obviously.