Wheel Stress

[Bakkerbaard]

In experimenting with docking ports, as mentioned in this topic I created, I managed to hook up two rovers. 

The stationary one is a massive beast, high tonnage, truck wheels, you know how that goes.

The docking one is a small material kit carrier, under ten tonnes. It sits on eight smaller stock wheels (the grey ones) and I'm thinking there in lies the problem. Through the movable Lynx docking port I can link them and the moment they turn into one vessel, the wheels on the Kit Carrier blow out. I'm guessing this is because of the little rover's new weight. If so, how the hell to I safely dock a small rover, or a transport rocket for that matter without it buckling under the weight of the massive tanks it's supposed to be drinking from.

On a side note, when I undock the Kit Carrier and repair the wheels, at wheel one it starts shifting. Like, moving, as if it's on ice. All wheels repaired and the shift stays, unless I drive it, in which case it'll pull to one side.

All of the testing has been conducted to the right of the runway at KSC on Kerbin. One Kerbal got lost.

[mystifeid]

Wheels have autostrut (heaviest part) enabled and maybe it is the realignment of the autostruts that makes the wheels blow out when the small rover docks to the big one.

As for pulling to one side, do you build the rover by adding wheels with mirror symmetry and is the controlling probe core aligned so that the navball is blue in the top half and brown in the bottom half?

[bewing]

Which version are you running? There was a fix for a wheel problem of that sort in 1.4.3.

 

[Bakkerbaard]

7 hours ago, mystifeid said:

Wheels have autostrut (heaviest part) enabled and maybe it is the realignment of the autostruts that makes the wheels blow out when the small rover docks to the big one.

Autostrut? I've heard about this on the forum, but I never really noticed it in game. Let alone in the wheel settings I've been seeing alot of lately. Is that a Settings Menu thing I could turn off? Do I want to turn it off?

7 hours ago, mystifeid said:

As for pulling to one side, do you build the rover by adding wheels with mirror symmetry and is the controlling probe core aligned so that the navball is blue in the top half and brown in the bottom half?

Yes and yes. The shifty behaviour only occurs after the wheel blow out.

5 hours ago, bewing said:

Which version are you running? There was a fix for a wheel problem of that sort in 1.4.3

Well, that's the problem right there then. I'm on 1.4.2. With the amount of time KSP swallows I always choose to just play instead of spending precious, precious time figuring out if i need to back up saves and mods and actually upgrading. ;o)

I'll get on it ASAP.

[Snark]

11 hours ago, Bakkerbaard said:

Autostrut? I've heard about this on the forum, but I never really noticed it in game. Let alone in the wheel settings I've been seeing alot of lately. Is that a Settings Menu thing I could turn off? Do I want to turn it off?

You can't.  Wheels and landing legs are configured to be "autostrut locked", meaning that they always have "autostrut to heaviest part" turned on and there's nothing you can do to change it.

11 hours ago, Bakkerbaard said:

I'm on 1.4.2.

Yeah, upgrade.  FWIW, the minor "point" releases of KSP usually don't do much to mess up mods-- my guess is that any mod that works in 1.4.2 will probably work fine with no changes in 1.4.3.  So you should be good to go.

(Keep your 1.4.2 install around, just in case, though.) 

 

[Bakkerbaard]

1 hour ago, Snark said:

You can't.  Wheels and landing legs are configured to be "autostrut locked", meaning that they always have "autostrut to heaviest part" turned on and there's nothing you can do to change it

What is autostrut anyway? I think I may have seen some mention of it somewhere in the game, but I always figured I had it off since I was pulling my own struts anyway. Does it even have anything to do with the support struts you use on rockets?

[bewing]

1 hour ago, Bakkerbaard said:

What is autostrut anyway? I think I may have seen some mention of it somewhere in the game, but I always figured I had it off since I was pulling my own struts anyway. Does it even have anything to do with the support struts you use on rockets?

The game engine that KSP uses (Unity), has a bug. The joints between parts are too flexible and do not dissipate energy when they bend. Unity may fix this bug someday, but don't hold your breath. This causes an additional problem with wheels flexing until they are not quite vertical and not quite facing forward anymore. Which causes un-tech-supportable problems with any wheeled vehicle.

So, out of the goodness of their hearts, the devs gave everyone a "temporary" slightly-kludgy workaround for all this called autostruts. Yes, they are just like the support struts, except they cost nothing and have no mass or drag and can be turned on and off in flight. Wheels are automatically autostrutted to the heaviest part in your craft always, no matter what you do, in order to work around the wheel-flexing glitch.

Depending on the difficulty level you selected for your game, and whether you have Advanced Tweakables turned on, and whether you've unlocked the normal struts in your tech tree -- you may also be able to optionally use autostruts anywhere else in your craft that you feel like.

Like anything else, there are pros and cons to using autostruts -- and to having them be automatic for wheels. But that's engineering for you. To make your ships work at peak performance, you have to understand the autostruts on it, and how they affect your design.

 

[Bakkerbaard]

16 minutes ago, bewing said:

autostruts

I think I understand, but I'm sure I won't when I check it out tonight. ;o)

I would like to take a moment to refocus on the bigger issue that remains: The stress that gets put on the little wheels when I dock a little rover with a massive one. Is there a way to avoid that? The way it looks to me right now is that I could only dock two similar rovers without one buckling under the weight of the other.

Or, to broaden the question, is there a way of transferring fuel or material I don't know of? I tried to connect two rovers with a yellow fuel line, hoping I could connect it like the portable struts, but obviously no dice. I thought I was right smart there.

[bewing]

Well, for connecting, there are klaws and there are modded hoses (since you are playing modded).

The traditional workaround for the bug is to make sure the wheels are off the ground at the moment that docking happens. If you then switch focus away (to the KSC or another vessel) and then switch back, then the bug won't happen.

 

[Bakkerbaard]

5 hours ago, bewing said:

then the bug won't happen.

I don't even think it's a bug, game-logic-programming-wise. Two vehicles become one and a bunch of wheels on it can't handle the pressure. Makes some kind of sense. 

So yeah, wheels off the ground. Like with lander legs, or those extendible stabilizers. It's gonna throw a wrench in my buglike-rover line of vehicles, but if I decide to go with esthetics instead of sensibility I'll keep an engineer handy. Now that the slidey-wheel bug is gone (I updated!) I can just fix 'em and drive off to flip over the whole thing. ;o)

[mystifeid]

33 minutes ago, Bakkerbaard said:

Two vehicles become one and a bunch of wheels on it can't handle the pressure. Makes some kind of sense.

I just tried sandboxing it. Made a 45t rover and a 3t rover. Bad things were happening docking and undocking at KSC. Tried side docking and end docking. Tried docking so that the little rovers wheels were off the ground. Sometimes I could get them docked with no damage but when I undocked a few things on the small rover would often explode and all 12 wheels on the big rover blew out. Probably was making some heinous mistake with it but I gave up in the end.

Edit: Before I was using 12 TR-2L wheels on the big rover and 4 M1-F wheels on the small one. Just tried again with 8 XL-3 wheels on the big rover and 4 TR-2L wheels on the small one. I must still be making some mistake though because bad things keep happening.

Edited June 2, 2018 by mystifeid

[bewing]

34 minutes ago, mystifeid said:

Bad things were happening docking and undocking at KSC.

Can you post some of your craft files? I'd like to see if I can reproduce any of that.

 

[mystifeid]

18 minutes ago, bewing said:

Can you post some of your craft files? I'd like to see if I can reproduce any of that.

They're very basic. Just try making one with Mk3 parts and the other one with MK1 parts. Stick a big fuel tank in the middle of the big one. Here's some screenies. Could this be happening because of the offset between the docking axis and the longitudinal axis of the large rover?

So with the bigger wheels, instead of just exploding on undock, the small rover is thrown around pretty violently - hence the feeling that I'm forgetting something.

Bad dock

Worse undock

Good dock. Problem solved.

Undock. Back to the drawing board.

Good dock with the bigger wheels.

Bad undock. Even the XL-3's are not unscathed.

Edited June 2, 2018 by mystifeid

[Bakkerbaard]

For the record, my docking process did not involve explosions. The principle's the same, but with me the little rover's eight TR-2L wheels would look just like in those pictures. The big rover was unscathed, however. And like I posted earlier, the problem is quickly solved with an engineer aboard.

[mystifeid]

13 minutes ago, Bakkerbaard said:

And like I posted earlier, the problem is quickly solved with an engineer aboard.

Really? On which rover?

Just tried it with 5 star Bill on the small rover and it docked and undocked ok but all 8 XL-3's blew out on the big rover.

Edited June 2, 2018 by mystifeid

[Bakkerbaard]

4 minutes ago, mystifeid said:

Really? On which rover?

I did my testing next to the runway on Kerbin, as I have not been able to get anything intact on active duty, so I don't know how much this information is worth in practice.

The big rover was always the one sitting and waiting. The little rover was the one doing the docking. Since that is lower to the ground I stuck the engineer in there. Upon docking the little rover will blow out it's TR-2L wheels. Then I undock the little rover, send the engineer on "EVA", fix the wheels and go about my business. Without the engineer, by the way; the ladder doesn't reach far enough...

Anyway, that's good enough for me, but it's not exactly a fix for the more explosive situation you have.

[mystifeid]

5 minutes ago, Bakkerbaard said:

send the engineer on "EVA", fix the wheels

Ah, ok. I thought you meant it fixed the problem. Amazingly it did fix it for my small rover (but I only tried it once) when I put Bill in it. When I put Bill in the big rover it was back to the usual story.

As an aside this was happening to my mobile bases on Eve when docking. My engineer would fix one wheel then another would blow out. Did that about fifty times. The same setup used to work (quite some time ago) and I just thought things must have changed. Should have added more wheels maybe. But perhaps that would have just given my engineer more wheels to fix.

[bewing]

1 hour ago, mystifeid said:

Just try making one with Mk3 parts and the other one with MK1 parts. Stick a big fuel tank in the middle of the big one. Here's some screenies.

OK, I'll give it a whirl this weekend.

 

[Bakkerbaard]

11 minutes ago, mystifeid said:

As an aside this was happening to my mobile bases on Eve when docking. My engineer would fix one wheel then another would blow out.

Yeah, the wheels are blowing out because you're docked. Undocking before repairs should solve that specific step.

[mystifeid]

25 minutes ago, Bakkerbaard said:

Undocking before repairs should solve that specific step.

Just that I had three that I needed to dock for a contract. They'd landed 5-10km apart (which on Eve, for me, is like hitting a couple of bulls-eyes) and when I got the first one to the second one I really wanted to dock them and drive them as one unit to the third one because it was pretty slow going. I also only had one engineer.

Edited June 2, 2018 by mystifeid

[Bakkerbaard]

10 hours ago, mystifeid said:

I really wanted to dock them and drive them as one unit to the third one because it was pretty slow going. I also only had one engineer.

Ah. I'm not thinking that big yet. The biggest achievement I had in this was the docking next to the runway.

[bewing]

On 6/1/2018 at 9:02 PM, mystifeid said:

Just try making one with Mk3 parts and the other one with MK1 parts. Stick a big fuel tank in the middle of the big one.

OK, issue confirmed and passed on to the devs for investigation.