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Reaction Wheel placement


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Good morning all. I am just about to send out my first Mun orbital probe, and was excited to unlock the SAS friendly Probodobodyne just in time. However, does it matter where on the ship it is placed? I'm wondering if reaction wheels function better installed in any particular region of the ship, or if it is simply a matter of them being somewhere on the ship.

Edited by GarrisonChisholm
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No, it doesn't matter where you place them. Regardless of where they are on your ship, they are equally effective, and your ship's center of rotation will be located at its center of mass.

(For reasonable ship designs. If you make something huge and long that's very floppy and has a tendency to flex and wiggle, then putting a bunch of reaction wheels in one section will tend to torque that section and affect the way your ship wobbles. But assuming you're making a "reasonable" ship that's pretty rigid, i.e. 99% of KSP ships, then it really doesn't matter.)

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For probes, placement doesn't matter. For larger ships it can. Reaction wheels generate torque at the part. Joints may wobble depending on their strength and the torque applied. When you have multiple wheels, gimbals, and/or an offset control reference the completing forces can create a positive feedback SAS control loop. Without intervention, such loops can destroy craft!

One word of caution for probes. When you work with less than a tonne, it is easy to have too much SAS. A dedicated reaction wheel could give you too much attitude control and make it real hard to precisely manuver. Instead, just rely on the probe core SAS.

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One more tip: if a reaction wheel gives you to much attitude control... and a probe core alone does not give you enough... then you can use a reaction wheel and reduce the control input by turning precision control on (hotkey: capslock by default). This also works with RCS.

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