SAS slow to move the ship in orbit ?

[Man in the Mun]

Hello.

Ive just built a Mun lander. It has a Advanced Inline Stabilizer and four RCS thrusters. However when changing the Navball mode from prograde to retrograde to manoeuvre. The ship is very very slow to move and at some points it struggles to hold the correct orientation.

What causes this and how do I fix it, please? 

I had a look in the VAB and the Advanced inline Stabilizer and RCS thrusters are much higher up than the centre of mass for that stage.

 

Thanks.

[bewing]

Did you actually hit the R key to activate the RCS thrusters? Usually RCS is an extremely powerful and fast way to rotate your craft. RCS often overcompensates. Reaction wheels are usually slow to do their job -- however, that's usually a benefit. It gives you a lot of fine control, especially if you are trying to change orientation by hand.

The SAS system uses a very generic algorithm for spinning a ship. If you want to go from prograde to retrograde and your ship turns slowly, then often the best thing to do is turn off SAS and pick a key such as D. Mash the D key until your ship has spun about a quarter of the way around. Let go, and wait until it spins another halfway by itself. Then turn on SAS and select the proper prograde/retrograde, and the SAS system will finish doing the turn itself. Or you can begin the slowing process yourself, since you know which key to mash to slow down again.

 

[Vanamonde]

So, problem solved? Yes, try adjusting the RCS placement. The position of the reaction wheel part is less important, though. Those will work pretty well no matter where they are. 

[Man in the Mun]

On 9/2/2018 at 7:13 PM, Vanamonde said:

So, problem solved? Yes, try adjusting the RCS placement. The position of the reaction wheel part is less important, though. Those will work pretty well no matter where they are. 

I think the problem was due to the length of the ship, when I decoupled stages it seems better. 

I dont know of a way to improve RCS control on big ships though ?

[sturmhauke]

25 minutes ago, Man in the Mun said:

I dont know of a way to improve RCS control on big ships though ?

I use the RCS Build Aid mod. It shows you if your RCS placement is causing unwanted translation or rotation. It also has a parachute helper that seems to work well.

[chico]

I think you should add another Advanced Inline Stabilizer. 15 kN of torque is probably not enough for your ship. I use 3 of the biggest 30 kN in some ships.