That damn runway! [VTOL SSTO Issues]

[jjmartin]

Hi folks!

 

I constructed my very first VTOL SSTO design yesterday--the fearsome Mk. 1 EX-1 Spaceplane.   This baby should get me basically anywhere in the solar system!  In the air it is rock solid, stable, nimble, and can hit the sonic thrust runway at 10-15 degree inclination with some loving care.    The VTOL system works flawlessly, and the rotating wing/engine assembly allows you to pull off some pretty insane manuvers.  The wings rotate to become legs, just the right height to lift most of the plane's weight off the wheels.  Retract the gear to set your wings to the last 5 degrees to ground perpendicular and blast off to about 450 feet or so and then rotate your wings back.  The orange bubs are droptanks for the initial VTOL from Kerbin--it does not quite have enough DV to VTOL and make it to orbit and then all the way to Minmus for refueling.  Those guys separate emptied immediately after VTOL.  It packs six junior drills, an ISRU, and a complete science package into about 60 tons.

 

I'm super proud of this guy!

 

There's one problem--when the game loads up the runway the plane immediately starts slowly turning left or right.  If left alone it will get completely out of control.  I can still take off VTOL no problem, and can manage a herky-jerk runway takeoff most of the time, but I want this one to be perfect and this is driving me nuts!

My legs are vertical, in symmetry, and placed with the snap tools so they should be aligned correctly.  I've tried playing with springiness and damping of the wheels, no change.  Disable the SAS, no change.  Everything is placed in symmetry and with snap.  I even remade the whole thing from scratch to make sure.

 

Also "Save game" has disappeared from my pause menu so I can no longer save during missions.  Man I love this buggy ass game.

 

Here's an album.  Anyone know what is going on here?  Album doesn't show it but eventually the plane just self-destructs.

If anyone wants the craft file I'm happy to share.  This thing is super capable and sexy as hell.  It does require Procedural Parts.

Edited December 27, 2020 by jjmartin

[FleshJeb]

First off, great documentation of your process. You could use a shot of the underside of the plane, but no big deal

I think you're overstressing your gear slightly. I'd guess your craft weights in excess of 50 tons, and the medium gear are only reliable to about 9 tons each. So, add more gear, fiddle with the settings a bit more, and see what happens.

FYI, my usual solution to bouncing is to turn Spring to 0.5 and Damper to 2.0 and go from there. I find Spring should always be less than Damper.

[jjmartin]

I love KSP...

 

So I placed four large gear on the plane and it started spinning in circles.  Deleted and replaced them with the same thing in the same place and everything is great now.  Thanks for the tip--this plane started with medium gear and got fatter and fatter until it outgrew them I guess!

 

-edit-

spoke too soon lol

This seems so random.   Veering everywhere again.  Even with large landing gear and no input other than brakes I spin in circles...

I can get it to stop moving by holding the brakes, but then it still rotates in a static circle.

Edited December 27, 2020 by jjmartin

[bewing]

2 hours ago, jjmartin said:

This seems so random.   Veering everywhere again.  Even with large landing gear and no input other than brakes I spin in circles...

This is a process I call microbouncing. The way that "contact with the ground" works in a game engine like Unity is that (during a physics timestep) gravity is calculated for each part. If the part ends up below the ground, it is moved back to the surface and given a small upward velocity. This makes the part fly through the air for a very short time, and then maybe sink below the ground again. During this time flying through the air, the part is not in contact with anything, and therefore has no friction. This is a fundamental problem with all game engines, as compared to reality. It is random.

[jjmartin]

So I am remaking it entirely again.

When I reconstruct just the fuselage and cockpit assembly (all snapped and symmetrical) I use about 10 parts including the large landing gear.

Still rotates, but slower.  I don't get it.  I've played with all the friction/spring/damper settings every way I can think of.

-edit-

Yeah... even with five large landing gears attached directly to the fuselage in any setting configuration I roll toward the KSC and rotate in a circle.  This has entirely stopped being fun.

 

Installed Kerbal Foundry for some wheels and got some that work a lot better but the plane will still turn in circles if left on its own.  loveing bizarre.

 

Edited December 27, 2020 by jjmartin

[FleshJeb]

4 hours ago, jjmartin said:

Yeah... even with five large landing gears attached directly to the fuselage in any setting configuration I roll toward the KSC and rotate in a circle.  This has entirely stopped being fun.

Now you might have too much gear on it. Although, it occurs to me that your robotic parts might be jittering in response to slight flexing and bouncing, and then reinforcing the behavior.

You can try this on the servos:

• Cutting the torque.
• Locking.
• Playing with the damper setting.

4 hours ago, jjmartin said:

This has entirely stopped being fun.

When I get stuck on a technical problem, I put it aside and go build something simple. By the time I come back to it, I've usually come up with a solution or different approach.

[jjmartin]

Thanks for the tips FleshJeb.

 

I'll come back in a few days when I am not gnashing teeth

[king of nowhere]

while this microbouncing problem is common, it is not normal that it is so persistent. generally with good landing gear you can stop it.

[Fierce Wolf]

On 12/27/2020 at 1:52 AM, jjmartin said:

Deleted and replaced them with the same thing in the same place and everything is great now

The old and faithful!