what is wrong with this rover?

[Lechu]

I created a simple rover to transfer ore from the miner to a craft.

 

But whenever it hits a small bump the large holding tanks get unglued from each other. All of it falls down and explodes.

 

[Linkageless]

I suspect there's a lot of weight strain on the joints.  Try enabling advanced tweakables, and set 'rigid attachment' and autostrut to 'Grandparent' on all your main structural components (ie ore tanks, z-4k, lander can, klaw and docking port).

You might also take some of the weight off the middle by adding wheels there.  If you want to keep just 4 wheels, perhaps mount them onto the middle two tanks then offset them to the outer ones.

[king of nowhere]

manually adding some struts to reinforce the structure also may help

[Lechu]

2 hours ago, Linkageless said:

I suspect there's a lot of weight strain on the joints.

You may be right, thanks. I just tested it with empty tanks, it was able to perform quite a jumps  without breaking apart. After some tweaking attachments of the wheels, that is.

Well, this thing is supposed to be used on Minmus.  Lower gravity there...

But, on the other hand, I don't want to be thwarted after hauling it all the way there.

[Linkageless]

It would have a lot better chance of surviving on Minmus due to the lower gravity.  Yet an impact at 10m/s, for example, would have much the same effect as it would on Kerbin or Eve.

Rigid joints might not be preferable for the wheels themselves, sometimes a bit of give is better.  Autostruts seem to lend a certain amount of strength and stiffness without making the thing completely rigid.  In short, it's worth experimenting with various combinations.

[VoidSquid]

You didn't use Bon Voyage by any chance? 

[Lechu]

16 hours ago, VoidSquid said:

You didn't use Bon Voyage by any chance? 

No, I don't. Have I created rover similar to one available in this mod?

[Mikenike]

26 minutes ago, Lechu said:

No, I don't. Have I created rover similar to one available in this mod?

What you can do is attach struts next time, lots of struts. Or use one of those girders, ore taknks on top, with batteries and probe core. then wheels on the middle section of the girders.

[Lechu]

If only KSP allowed more then just one joining point between two parts...  This is the single most annoying limitation of this game.

[Linkageless]

There is the option of adding physical struts - that arguably provides more than one joint.  This would potentially be another solution to your original problem.  Maybe even a more Kerbal solution!

Edited September 22, 2020 by Linkageless

[FleshJeb]

On 9/21/2020 at 10:46 AM, Linkageless said:

rigid attachment

Never, EVER use Rigid Attachment, it turns your craft into glass--Hard but brittle.

The only justifiable use case is for mechanical contraptions using Same Vessel Interaction that require tight, consistent tolerances to function.

The issue in this case is that the full ore tanks are so dense that they overcome the attachment strength. They're not really suitable for structural uses. It would be better to build a chassis out of girders and hang the tanks from that chassis.

[Spricigo]

8 hours ago, Lechu said:

If only KSP allowed more then just one joining point between two parts...  This is the single most annoying limitation of this game.

There is a mod for that 

If mods are not an option you may use the Big White Structural Part as a backbone and radially attach the ore tank to it to it.

Spoiler

 

 

[Linkageless]

9 hours ago, FleshJeb said:

Never, EVER use Rigid Attachment, it turns your craft into glass--Hard but brittle.

The only justifiable use case is for mechanical contraptions using Same Vessel Interaction that require tight, consistent tolerances to function.

I'll agree that rigid attachment may be over the top for this, and may even have a negative effect given that they remove a lot of the springy resilience that normal joints, struts and autostruts provide.  I wouldn't agree that they should never be used.  I've found there's more than just mechanisms that may need consistent tolerances, for example if you wish to reduce/remove wing flex.  Sometimes, keeping certain parts rigidly together is what you want to prevent additional strain on other parts.

I would encourage the OP to experiment with what works best, as learning what works best in various situations is one of the fun bits.

9 hours ago, FleshJeb said:

They're not really suitable for structural uses. It would be better to build a chassis out of girders and hang the tanks from that chassis.

Not suitable for structural uses is open to debate.  The thing about KSP parts is that almost all are useful building blocks, their suitability depends on what they need to support. The Ore tanks' mass when full certainly makes them a bit of a liability in this case and adding a supporting structure seems an excellent suggestion to mitigate this.

Has anyone produced some good KSP assembly structural strength experimental reports along these lines?   There's an awful lot of combinations but it would be great to have rules of thumb for things like impact resilience and bending strength with various components and joint settings.

[VoidSquid]

Tried this mod? 

 

[Okhin]

4 hours ago, Linkageless said:

Has anyone produced some good KSP assembly structural strength experimental reports along these lines?   There's an awful lot of combinations but it would be great to have rules of thumb for things like impact resilience and bending strength with various components and joint settings.

From my experience, when working on refuellers and things that I will fly more than once and which have a lot of change in mass (like those Ore Tanker I send to orbit), I tend to avoid using tanks for structural elements. I use Girders, the XL ones, and I put rigid attachment Activated on it. And on those frame I put my wheels, landing legs and propulsive system (i tend to use the throttle as a on/off switch, which might lead to some issue related to accelerating heavy parts too much), and then I strap tanks to this rigid structure (and then, I do not use rigid attachment on that).

It removes a lot of global wobliness, even if tanks might wobble on their own, enough SAS usually compensate for that, and the integrity of the craft is not at risk. And I have a liberal use of the EAS strut, to attach those tanks to the main frame.

Also, it seems that putting your tanks inside cargo bays make everything sturdier (but still, my wheels are attached on a frame on top of which I put my cargo bays, inside of which I put my ore tanks for instance). But I think cargo bays are kind of a magical tech that can be used for a lots of stuff (including heatshield, aerobrakes and balasts).

In short: Build a rigid frame for your craft, and on top of that, straps whatever you want on it. A bit like cars are made in fact. Or even bikes.

[Lechu]

Thank you all. This one behaves much better. It still can disassemble when trying too high a jump, but it is not supposed to be a hotrod.

3 hours ago, Okhin said:

In short: Build a rigid frame for your craft, and on top of that, straps whatever you want on it. A bit like cars are made in fact. Or even bikes.

It is interesting stuff. While I don't want to redesign my Minmus ore hauler, it is worth to keep it in mind for future constructions. Like the craft that will haul the ore form the Minmus  surface to the orbit processing centre .

 

Speaking of which. I have an extension to a Minmus orbital station on the way already. And I have used there rigidly connected large ore tanks. Do you think I am going to run into troubles once the tanks are full?

The part on the left of the HubMax is already on the Minmus orbit. The part on the right in on its way there.

Edited September 23, 2020 by Lechu

[Spricigo]

12 hours ago, Lechu said:

Do you think I am going to run into troubles once the tanks are full?

Maybe. There is quite a lot of parts to eventually fail in unexpected ways.

Have you considered to test it in a sandbox save before flying it to Minmus?

[Lechu]

11 hours ago, Spricigo said:

Have you considered to test it in a sandbox save before flying it to Minmus?

I don't have sandbox save, as yet. I have thought that I finish Career mode at least once, before going into Sandbox.

Edited September 24, 2020 by Lechu

[Spricigo]

8 hours ago, Lechu said:

I don't have sandbox save, as yet. I have thought that I finish Career mode at least once, before going into Sandbox.

Well, it's your decision, but I have thousands hours played and no idea of what  "finish career" is supposed to mean. 

[Klapaucius]

My experience in building craft with ore tanks, including rovers similar to yours, is that there is something inherent in the ore tanks that just makes them come apart.  I have no idea what is going on under the hood (I am not a coder) but they break a lot. I suppose it could just be the added mass, though one would think fuel tanks would do the same.  My solution has been to use a lot of struts.