RCS Improvement

[Styrr]

Hello everyone. I'm an absolute newbie in KSP modding and have a question regarding the module development. I sometimes come into certain issues with RCS: When they are not placed in the correct distance to the CoM the behaviour gets rather annoying. I know of the RCS Build Aid and the PWB Fuel Balancer mod which allow me to place the RCS in optimal places and help by keeping the CoM as desired by shifting fuel loads. However, this leads to designs where I have to place the RCS units near to other components in my spacecraft.

When turning off SAS my experiments show that for rotational controls the CoM position of the is taken into account. However, for translational commands this doesn't seem to be the case.

Here are some examples on the behavior:

Yaw Motion using the RCS works nicely and takes CoM into account (here i request yaw):

Translational motion (right) does not take CoM into account and introduces heavy rotation (here i request translation to the right):

Translational motion (right) with SAS turned on starts as above without taking CoM into account and starts to counter the introduced rotation by thrust in opposite direction. The up/down thrusters are only marginally used. This is on the one hand meaningful since the lever is small for those and they are not very efficient. However, it would be much better to use them anyway instead of thrusting in the opposite direction, cancelling the the desired translational motion completely

Translational motion to the right (blue arrow) with a different setup where you can see the SAS result (the actual SAS thrust in white), where the pink arrows show (qualitatively) how you could control the craft in a more effective way.

My request in this thread is twofold: On the one hand I'd like some feedback if my thoughts are correct or if I made a mistake in my conclusions. On the other hand I'd like to ask - given my thoughts were correct - whether there are mods trying to tackle this? And: If I knew how to mod, would it be possible to somehow get between the controls and the RCS actions?

[pizzaoverhead]

RCS used to do CoM lever-arm compensation but was changed in 18.2 to the current system due to an infinite thrust bug. The old system is still available though: It's activated when using fine control mode (Caps Lock). Does that mode improve the situation any for your tests?

[Styrr]

Indeed the behavior changed. When looking at the last setup with 8 RCS blocks the one nearer to the CoM uses more thrust than the one at the bottom.

It does not however apply thrust in the inverse direction to really counter the introduced rotation. Nor does it use the up down thrust to counter the rotation.