Why does this craft spin?

[THX1138]

This craft spins quickly as though I was holding onto Q or E (except far more torque than my reaction wheels can manage). I don't understand why. I could understand the COM was misaligned with the CoT and it might spin as though I was holding W or S but it doesn't. It spins on a completely different axis.

Youtube video to show axis of spin: https://youtu.be/v-sixtvzcrQ

Edited May 16, 2015 by THX1138

[Guest Darth Gerbil]

Press alt-x.

[THX1138]

Press alt-x.

There's no trim set so, perhaps predictably, this doesn't help but thanks for replying.

[Guest Darth Gerbil]

Sometimes the gui freezes, or some parts could be colliding and creating a phantom force.

Do you mean it spins when the engines are firing?

[THX1138]

Sometimes the gui freezes, or some parts could be colliding and creating a phantom force.

Do you mean it spins when the engines are firing?

Yes, only when the engines are firing.

[Alshain]

You were right, it is your center of thrust. A craft with a stack engine will indeed spin as though pressing W and S if the center of thrust is not in alignment, but you aren't using a stack engine, you are using radials. Because there is more mass on one side than the other, the radial engines on the side with greater mass would have to be thrusting harder than the engines on the side with less mass to maintain equilibrium.

[Windspren]

The wheels could be creating torque, or your engines could be misaligned. It's probably the wheels though.

[Nutter]

In that case, did you go and check it's thrust and mass alignment? From the materials lab and drill, I'm guessing the thing is at least partially asymmetrical.

Are the long girders massless, by the way?

[THX1138]

I'm not sure everyone is clear on the axis of rotation. Here it is in video form: https://youtu.be/v-sixtvzcrQ

If the CoM and CoT were the issue, I would only expect rotation in the W-S or A-D axis. I don't understand the rotation in Q-E axis.

If the CoT needs to be adjust, I can try throttling engines but my attempts so far have not had any affect. Could it be because the probe core is not aligning correctly with CoT/CoM and therefore tells the engines to gimbal in an inappropriate way?

I am already dealing with prograde and retrograde markers pointing the wrong way because the probe core doesn't understand it's own or the engines orientation.

Edited May 16, 2015 by THX1138

[cybersol]

I'm not sure everyone is clear on the axis of rotation. Here it is in video form: https://youtu.be/v-sixtvzcrQ

Hard to tell definitively, but one engine looks to have a bad rotation angle. Its the one that starts on the lower right in the video. As it spins to the top you can see its thrust going in a slightly different direction than the other engines.

[tater]

Are the wheels spinning forward? Right hand rule. If so, the wheels are exerting a torque, and the set farther from the CM has a longer level arm.

[THX1138]

The wheels aren't spinning. I experimented with the brakes and that didn't help.

I've locked gimbal on the engines and that seems to have resolved the problem. I also checked in the SPH and adjusted the thrust to get the CoT and CoM better aligned but I don't think they were really the problem anyway.

Thanks to everyone for the suggestions.

[adinfinitum]

Even though it stopped when you locked the engine gimbal, that doesn't solve the root of the problem. After watching the video and looking at your ship, it looks like the problem is the placement of your engines. The engines are all lined up along the axis of the CoM, but it looks like 3 sets are slightly above and 1 set is slightly below the CoM. Because of the way the game flips the way the gimbals turn based on whether the engine is below or above the CoM, you end up with 3 sets pointing one way and one set pointing the other way. I'd move the set on the 2.5m tank up some, and I think that should let you leave the gimbal on.

[THX1138]

Even though it stopped when you locked the engine gimbal, that doesn't solve the root of the problem. After watching the video and looking at your ship, it looks like the problem is the placement of your engines. The engines are all lined up along the axis of the CoM, but it looks like 3 sets are slightly above and 1 set is slightly below the CoM. Because of the way the game flips the way the gimbals turn based on whether the engine is below or above the CoM, you end up with 3 sets pointing one way and one set pointing the other way. I'd move the set on the 2.5m tank up some, and I think that should let you leave the gimbal on.

Thanks; I'll take a look at that.