Parts & Vessels Gimballing engines apply a slight force to a vessel when turning even when they're not burning

[JtheHorn]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 10, 64bit | CPU: 11th Gen Intel I7-11700 @ 2.5GHz | GPU: NVIDIA GeForce GTX 1660 SUPER | RAM: 16 GB

 

Severity - Low

Frequency - High

When engine gimbal is enabled and you turn (no thrust), a slight force is applied pushing this vehicle in the opposite direction. If also slowing the turn the same way then the 2 forces balance out. However it can mess with precise operations like rendezvous.

 

Included Attachments:

Edited December 25, 2023 by The Space Peacock

[The Space Peacock]

do you have any footage of this that could clarify whats happening?

[MechBFP]

This was driving me nuts when I was trying to dock a rather unwieldy vehicle the other day, I didn’t understand why I was getting translational movement when just rotating the craft, and this explains it. 

[JtheHorn]

I'm sorry I don't, maybe ask @MechBFP since he was having the same issue.

[NaughtyMonster]

On 12/26/2023 at 1:01 AM, MechBFP said:

This was driving me nuts when I was trying to dock a rather unwieldy vehicle the other day, I didn’t understand why I was getting translational movement when just rotating the craft, and this explains it. 

Is this what causes the velocity vector to wander around when you rotate your craft during a docking approach? It was driving me crazy too!

[testunde]

Same here while doing rendezvous, even with smaller crafts. Maybe I am able and remember myself to get some footage after the holidays.

[JWag]

Yes! It can be reproduced somewhat easily, I think, with typical Medium size Apollo-like vessels based on the 3-seat capsule and 2-seat lander can.

When the navball is in Target mode and you're approaching your docking target at a very low speed (i.e. ~0.5m/s or less) and just using reaction wheels (RCS off) to orient, you'll see the target icons moving all over the place as you pitch and yaw.

I really thought I was just super rusty at rendezvous, but phantom forces explains what I was seeing. I guess I'll have to get back in the habit of disabling engine gimbals when not under thrust. The new gimbal sound effect is kind of annoying.

[JWag]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 11 22H2 | CPU: Intel i7-12700F | GPU: AMD Radeon RX 7700 XT | RAM: 32GB

 

Title: Phantom translation forces from engine gimbals or reaction wheels

Specs: Intel Core i7-12700F, 32GB system RAM, AMD Radeon RX 7700 XT on Windows 11 22H2

Severity: Low

Frequency: High

Description:  I had thought the phantom forces I was seeing were because of the engine gimbals, but I'm less sure now. I think it may be because of reaction wheels? Not sure if this is what the OP and others were seeing, but in this case it doesn't seem to be caused by the engine gimbal as much as the reaction wheel.

To Reproduce:

1. Load the attached craft file, launch with a kerbal in each capsule, and cheat into orbit of say, Minmus.
2. Undock one ship, set the other ship's docking port to Target, and change the navball to Target mode.
3. Use RCS to back the ship away 20-30m, then stop
4. Activate engine so that it gimbals.
5. Thrust toward target vessel and disable RCS when approach speed is ~0.2m/S
6. (The target vector should mostly align with the ship's prograde vector.)
7. While on approach, apply pitch and yaw to the craft and watch the target vector flail around wildly
8. Repeat steps 2-7 after docking while enabling/disabling the engine gimbal, capsule reaction wheels and/or SAS.

This used to happen in KSP1, but with much less magnitude.

 

Included Attachments:

Phantommenace.json

Edited December 27, 2023 by The Space Peacock

[The Space Peacock]

@JWag merged your report