Docking on the Surface (Rovers)

[18Watt]

I am trying to dock vessels on the surface (any body), the purpose is to transfer fuel from ISRU mining/refining equipment to spacecraft.  Rather than trying to make all my vessels have docking ports at exactly the same height and orientation, I'm trying to use the robotic parts to facilitate docking port alignment.

The problem is that there is a bug when docking rovers on the surface using robotic parts.  The bug usually results in the total destruction of one or both vessels.

The bug was reported on the tracker here: https://bugs.kerbalspaceprogram.com/issues/23177

There have been a few threads discussing the issue, here's one of them:  

I am still struggling with this bug, and have not found a satisfactory way to dock vehicles on the surface.  Using the 'Klaw' instead of docking ports doesn't help, the same ship destruction occurs.   I am looking for suggestions to successfully dock vessels on the surface, I'm hoping someone has found a way to mitigate the surface docking bug.

I realize there are several mods which would make surface refueling possible.  I do not use mods, so that suggestion would not be helpful to me- although other players may find those suggestions helpful.

Any suggestions for docking surface vessels (rovers, or rover to large ship) would be appreciated.

[Zhetaan]

35 minutes ago, 18Watt said:

I am still struggling with this bug, and have not found a satisfactory way to dock vehicles on the surface.  Using the 'Klaw' instead of docking ports doesn't help, the same ship destruction occurs.   I am looking for suggestions to successfully dock vessels on the surface, I'm hoping someone has found a way to mitigate the surface docking bug.

I realize there are several mods which would make surface refueling possible.  I do not use mods, so that suggestion would not be helpful to me- although other players may find those suggestions helpful.

Any suggestions for docking surface vessels (rovers, or rover to large ship) would be appreciated.

Since I am uncertain of what you have tried and what you've found to work or not work, I can only go by the information in the bug report:  it appears that you have three choices for workarounds.  First, you can eliminate the mass disparity between the vehicles, which might necessitate inert ballast on one of them.  Second, you can redesign to eliminate robotic parts, since the problem appears to be isolated to designs with those parts.  Third, you can redesign so that you can dock while your wheels are retracted.

I don't like number one because it both complicates design and is tailored to exactly one situation in which you would use the rover, thus requiring a custom solution for every mass combination.  That said, you could make it work by keeping the ISRU as a separate module and using the rover to haul both ore and propellant.  You'd need to have a balanced transfer shuttle too, though, so it's a bit more complicated than just balancing the converter/power-plant against the mobile-drill/tanker, but provided that a drill rover with a full tank of ore masses the same as the ISRU plant, then the finished propellant will have the same mass as the ore.

I don't think you'd like number two, since it puts you back in the position of needing to get exactly the same height and orientation, as you put it.

For my part, I would choose number three and have the rover able to lower itself onto skids or a stationary cradle in preparation for docking.  These can be incorporated into the rover's underbelly and made a part of the docking process.  You may lose some utility as you're more likely to beach your rover when going over ridges and other rough terrain, so you'll need to consider it carefully, but you can justify it as having the rover assume a needful bracing position prior to a major mass transfer as would occur in offloading a tank full of ore or some such.  If real cargo haulers need to 'block' their wheels, as it were, before moving mass around, then it's no loss for you to do the same.

[king of nowhere]

I have done docking among rovers for a while in my career before moving away from it.

short answer, there is no solution that I know. The only thing I can recommend is to save the game before attempting the docking, and reload if the bug engages. it doesn't always happen, so you can get away with it.

dampening the suspension on the wheels should also help, as the rover "jumping" is caused by wheels appearing underground for a moment and giving  jolt to the suspensions.

I have found anothe rbug, engaging whenever i dock ships with robotic parts close with the docking ports, and resulting in the robotic parts getting scrambled, and it's the main reason I stopped doing that kind of docking. but other players apparently don't have it

[18Watt]

3 hours ago, Zhetaan said:

For my part, I would choose number three and have the rover able to lower itself onto skids or a stationary cradle in preparation for docking.  These can be incorporated into the rover's underbelly and made a part of the docking process.  You may lose some utility as you're more likely to beach your rover when going over ridges and other rough terrain, so you'll need to consider it carefully, but you can justify it as having the rover assume a needful bracing position prior to a major mass transfer as would occur in offloading a tank full of ore or some such.  If real cargo haulers need to 'block' their wheels, as it were, before moving mass around, then it's no loss for you to do the same.

This is the direction I’m leaning towards.   There’s a couple of obstacles I’m having trouble with.

The only stock rover (powered) wheels which are retractable are the ‘Apollo’ style wheels.   They are a bit small for the weight of the fuel truck I’d like to have, even on Minmus.  Using bigger wheels would require an alternate method of retracting the wheels, or lowering skids to raise the wheels off the surface.   I haven’t built a vehicle like this, but will give it a try tonight.

Thank you for the reply.

[Spricigo]

My solution for that kind of problem it's to arrange the docking ports pairs so one vehicle has it pointing Up while the other point Down. One of the craft is capable of raising/lowering itself when the other get in position above/below it

Most likely to not include robotics parts in the elevation/lowering mechanism while the risk of bug persists.

[Wobbly Av8r]

16 hours ago, 18Watt said:

Any suggestions for docking surface vessels (rovers, or rover to large ship) would be appreciated.

I've had very good success docking ports and klaws on the surface. Given the issues others are experiencing, this could be just lucky happenstance but after looking at the various configurations, I think the answer is (short version) docking ports should be mounted so that only horizontal forces are involved, NOT vertical forces. This solution, however, does require some level of pre-alignment during construction. I've included a shot of one of my implementations...

Spoiler

The not-so-short version reasons like this:

When docked, what was two vessels are now considered a single vessel and the forces upon the docking port or klaw appears to be mostly shear and/or torsional (KSP parts don't crush or stretch apparently). However, *AT THE MOMENT* you undock, the interaction of forces between two vessels is *immediately* calculated and, given that wheels and landing gear have springs/dampers that store energy/force, Newton rather accurately predicted that your lighter 'm' will succumb to your accumulated 'F' with a significant 'a'.

The solution is to prevent those forces from accumulating in the vertical plane (the plane through which gravity acts - and increases with load/mass) which is easily achieved with horizontally mounting docking ports. This does, however, require some alignment during assembly which you don't want to do, but in reality is not too difficult but does require some planning.

Even with construction alignment, the ports will likely not mate perfectly as illustrated in my image - but by adjusting the spring strength of the landing gear and/or deploying/retracting drills a slight movement typically allows the docks to merge - heck, sometimes just the little bounce you get from switching from one vessel to another is enough to trigger the docking completion...

Edited November 25, 2020 by Wobbly Av8r

[vv3k70r]

16 hours ago, 18Watt said:

The problem is that there is a bug when docking rovers on the surface using robotic parts.  The bug usually results in the total destruction of one or both vessels.

This is not a bug. Its design of vessel.

You can solve it that way:

 

[jimmymcgoochie]

I once tried to build a mining rig on the Mun using a series of modular rovers and a bunch of laws attached to robotic parts. Terrible frame rates, stability issues (the little rovers with just klaw arms were bouncing all over the place) and in the end I binned the whole thing after it tore itself apart.

Now I use the SimpleLogistics mod, which lets nearby landed vessels share and transfer resources without having to be physically connected to each other. They’re all still within physics range so having lots of high part count vessels in close proximity will still make the game go slow, but they won’t spontaneously disassemble each other as they tend to when connected up by robotics and docking ports or klaw.

[18Watt]

5 hours ago, vv3k70r said:

This is not a bug. Its design of vessel.

You can solve it that way:

 

Thank you vv3k70r!  That helped greatly!

I did have to add one further step to your suggestions in your post.  Here is what I did (as suggested by vv3k70r):

1.  Create an action button which deactivates all robotics motors (hinges, servos, hyd cylinders...), and deactivate them just prior to docking.

2. Reduce damping on all robotics parts to zero.

3. Reduce damping on all rover wheels to minimum- 0.05 is the lowest damping the wheels will go.  

I managed successful rover dockings using those steps.  Rover wheels with no damping makes the rover very bouncy, but I can work with that.  This is a solution I can use.  Thank you again.