Symmetrical Servos: Only one moves

[KevinW42]

I'm trying to make a VTOL spaceplane with tilting engines, but one of the servos isn't behaving properly.

In the editor everything works as you'd expect:

 

But in flight only one of the engines moves:

 

I've tried turning off rigid attachment and autostrut, but it made no difference. I also tried removing the servos from symmetry, but that didn't work either. All the settings for both of them are identical. Weirdly, both servos consume power when I change the target angle, but the stationary one consumes less. Any Idea how to fix this?

[Guest]

Which version are you using? This was broken for several versions (without an easy workaround) but is working fine for me since 1.11. 

[KevinW42]

16 hours ago, Brikoleur said:

Which version are you using? This was broken for several versions (without an easy workaround) but is working fine for me since 1.11. 

 

Spoiler

 

Ah, I'm still on 1.8. I guess that explains it. I think I figured out a workaround by allowing full rotation and using the KAL-1000 to set the angle instead but I'll have to test that later.

 

(Edit) Yup, that worked. If I allow full rotation and remove the angle limits the KAL-1000 seems to control both servos just fine.

Edited January 23, 2021 by KevinW42

[Wobbly Av8r]

Actually, I think your problem is similar to my problem (I'm running 1.10 but I've had the same kind of problem since I can remember.)

It has to do with the symmetry and how it's built in the VAB/SPH and the solution I've found is to build only one side of the symmetrical structure (in single symmetry) all the way through, i.e. normally you would place two servos, then two engines, and so on, but I would build ONE side of your symmetry, THEN turn on double symmetry and select the root part of the symmetrical structure and place it back down so that the OTHER side is created all at once. Then it behaves like you would expect.

Interestingly, in my experience, if you edit an outer portion of the symmetrical structure after original placement as described, you end up with the same problem again, so if you have to change ANYTHING on the symmetrical structure, you have to edit the portion and then place it ALL again in desired symmetry. Don't know why, but it works.

[KevinW42]

2 minutes ago, Wobbly Av8r said:

Actually, I think your problem is similar to my problem (I'm running 1.10 but I've had the same kind of problem since I can remember.)

It has to do with the symmetry and how it's built in the VAB/SPH and the solution I've found is to build only one side of the symmetrical structure (in single symmetry) all the way through, i.e. normally you would place two servos, then two engines, and so on, but I would build ONE side of your symmetry, THEN turn on double symmetry and select the root part of the symmetrical structure and place it back down so that the OTHER side is created all at once. Then it behaves like you would expect.

Interestingly, in my experience, if you edit an outer portion of the symmetrical structure after original placement as described, you end up with the same problem again, so if you have to change ANYTHING on the symmetrical structure, you have to edit the portion and then place it ALL again in desired symmetry. Don't know why, but it works.

I think I ended up doing something like that in the process of trying to troubleshoot, but it didn't work for me. Though I actually did end up finding a solution, which I've edited into my previous post.

[vv3k70r]

On 1/22/2021 at 10:56 AM, KevinW42 said:

But in flight only one of the engines moves:

Autostrut - granparent or not att all. For all moving parts. All including servo.

Hierarchy of objects conections. Struts change dependency for degree of freedom.

By autostruts on moving part You conected it to something else - if they do not break (Kraken like it) it will not move. In Your case You conected it to root part.

Servo also cannot have autostruts to root, because one part of it must move. And no other parts on moveing objects (shock cones fe) should not have anything more then grandparent autostrut.

 

Check also if Your engines are not the heaviest part, because other pieces would strut to them.

Edited January 25, 2021 by vv3k70r

[KevinW42]

On 1/25/2021 at 3:28 AM, vv3k70r said:

Autostrut - granparent or not att all. For all moving parts. All including servo.

Hierarchy of objects conections. Struts change dependency for degree of freedom.

By autostruts on moving part You conected it to something else - if they do not break (Kraken like it) it will not move. In Your case You conected it to root part.

Servo also cannot have autostruts to root, because one part of it must move. And no other parts on moveing objects (shock cones fe) should not have anything more then grandparent autostrut.

 

Check also if Your engines are not the heaviest part, because other pieces would strut to them.

Autostrut wasn't the issue. Setting the servo autostrut to heaviest part did lock both of them up, but even with autostrut turned completely off on all parts I still had the problem where only one servo would move. After using my workaround with the KAL-1000 everything worked just fine, even with the servo autostrut set to root part.

[Spricigo]

10 hours ago, KevinW42 said:

even with autostrut turned completely off on all parts I still had the problem where only one servo would move.

There is any landing legs/gears in the craft?

If memory serve me well, there was an issue with legs/gears that prompted the creation  of autostruts as a fix, and those are always strutted to heaviest part (may it be the engine in your craft?)

[KevinW42]

45 minutes ago, Spricigo said:

There is any landing legs/gears in the craft?

If memory serve me well, there was an issue with legs/gears that prompted the creation  of autostruts as a fix, and those are always strutted to heaviest part (may it be the engine in your craft?)

There was no landing gear when I did the tests in the screenshots, but once I found a solution it worked with or without landing gear.

[Fierce Wolf]

I'm using 1.11 and symmetrical servos are broken. Upon creation and deploy, everything seems right. However, if you load a quicksave, your craft will be possesed by a tiny kraken