My large ships won't turn

[Eleven]

I'm guessing it's because they are so large but I'm having serious issues getting vessels to respond while trying to make moves in space. I've had this happen on several large ships. All have plenty of electricity, RCS fuel and jets, and SAS just doesn't seem to work at all sometimes. Mechjeb can't even get them to turn most of the time.

I actually had one ship, on the long time warp to Eve just become dead in space. I quit the game and restarted and it was fine after that, I'm assuming that is a bug. But the large vessles taking so much time to turn towards a node sucks when you actually miss the node because of it.

[rryy]

Try putting on some more command pods/probes to increase the turning torque. The normal SAS module only slows down rotation when activated.

[Atanar]

The placement of the RCS matters a lot. If you want to turn you should place thrusters in 4-symetry somewhere away from the centre of mass. Same goes for the command module torque.

[Merinsan]

You don't want SAS on for turning, and SAS modules don't help.

Command pods have a lot more torque than probes.

RCS port placement is very important. While linear ports offer more thrust, the 4 way blocks give much more control. I normally have 8 4-way blocks on my rockets, in 2 sets of 4. 4 at the top, 4 at the bottom in 4 way symmetry.

The last thing you can do is if you have gimballing engines is to throttle up slightly and start turning using that. I do this when I am desperate.

[Eleven]

Does RSC get used when just turning the ship to face a node? I don't ever see the animations from the RCS thrusters like I do when I'm docking.

[Eric S]

RCS works for both translation and rotation when it's on.

[Jason Patterson]

Does RSC get used when just turning the ship to face a node? I don't ever see the animations from the RCS thrusters like I do when I'm docking.

As long as RCS is turned on it will help you turn, regardless of the purpose of the turn.

[loiske]

In the big ships it also helps to place the rcs thrusters as far a way from the center of mass, as this creates more momentum with less force

[Eleven]

As long as RCS is turned on it will help you turn, regardless of the purpose of the turn.

If that is the case, then I never use RCS to turn my ships to face a node, turn retrograde or anything other than docking. If RCS was supposed to be used to do these other manuevers, why doesn't MechJeb use it? (BTW, mechjeb can't turn my large ships either, and it has control of RCS doesn't it?)

[loiske]

If that is the case, then I never use RCS to turn my ships to face a node, turn retrograde or anything other than docking. If RCS was supposed to be used to do these other manuevers, why doesn't MechJeb use it? (BTW, mechjeb can't turn my large ships either, and it has control of RCS doesn't it?)

I think youl have to toggle rcs manually with mechjeb, to prevent accidental usage of monopropellant

[DerekL1963]

If that is the case, then I never use RCS to turn my ships to face a node, turn retrograde or anything other than docking. If RCS was supposed to be used to do these other manuevers, why doesn't MechJeb use it? (BTW, mechjeb can't turn my large ships either, and it has control of RCS doesn't it?)

MechJeb will use the RCS if you've turned it on. Otherwise it uses gimbaled engines and command pod/probe body torque.

[Eleven]

I don't think I'm relaying my issue correctly. I can't even get a ship to rotate effectively. It takes forever to change a ships direction to face a node, go prograde or retrograde...once I finally do get to those points, things work great, but getting my ship pointed where I want it too takes so long it seems something is wrong. Even with MechJeb if the ship is trying to face a node, or turn retrograde, it misses the mark, swings way past and then rebounds back and forth, very very slowly until it finally reaches the target on the navball.

I don't think this has anything to do with RCS. But I could be wrong.

[EinQuant]

Maybe you could post a screenshot of one of your ships while turning? That would help us to help you

[smunisto]

The heavier your ship is, the slower it will turn of course. Without RCS you rely only on pod/probe body torque which is extremely tiny. Try a smaller ship and you will see how much more responsive it is.

The overshooting of marker is normal too. To stop the turn/rotation you require the same amount of force applied in the opposite direction of the turn/rotation. You can't expect to spend 10 seconds starting your ship to move and being able to nail it on the marker dot, like it's made of paper.

This is not a bug, and MechJeb by no means is explanatory for any physics laws in the game. Besides, as stated in previous posts, MechJeb will not use RCS if you don't turn it on.

RCS is made exactly for big ships, all rotations and turns are translation maneuvers and require proportional amount of RCS to maintain better control over your ship in the vacuum of space, when your engines are turned off.

[sumghai]

I'll echo the others' sentiments that placing RCS thrusters further out on a large ship / structure may help. The space station I'm currently assembling in orbit has generous numbers of thrusters on every module, such that I can rotate the entire station to whatever orientation I want reasonably quickly.

Edited May 17, 2013 by sumghai

[Eleven]

Here is a SS of one of the ships that just don't like to turn. It has plenty of RCS thrusters and I tried turning RCS on to change from Retrograde to Prograde and it took about 1/4 of my RCS fuel just to do that once. Doesn't seem like that should be the case, how many times do you have to turn your ship just on one mission? Not to mention docking, it would mean that I need to carry as much RCS fuel as I do Rocket fuel.

This second image is when I'm using RCS to make the change from Retrograde to Prograde.

Edited May 16, 2013 by Eleven

[smunisto]

Man, these are heavy ships, they are using the biggest 2.5m tanks, even if the propulsion ship has just half of it. They weigh more than 120t for sure. It's absolutely normal for them to take like 10-15 seconds to turn from prograde to retrograde and being unable to stop. For such ships you would need atleast 2000 monoprop.

[Eleven]

Man, these are heavy ships, they are using the biggest 2.5m tanks, even if the propulsion ship has just half of it. They weigh more than 120t for sure. It's absolutely normal for them to take like 10-15 seconds to turn from prograde to retrograde and being unable to stop. For such ships you would need atleast 2000 monoprop.

Here are the ships' stats. I have a few that are this large and they all act sluggish. I think I need to find a balance for the number of RCS ports I have, too many and you just blow through your RCS fuel. All the RCS I have used so far was used to dock them originally, and then to try and use the RCS to turn the entire ship around for the purposes of testing for this thread:

BTW, 234 tons, it's heading to Eve Orbit for refueling. I have another, larger ship there now that used most of it's fuel just to get to orbit, I can't land or leave until I refuel

[Whatshtisthis]

For your large ships, try using the RCS parts that only release monopropellant in one direction, you might save some monopropellant with that.

[Psycho0124]

Pop some empty cockpits or probe cores on that thing. The extra torque will help you turn it and you don't need to worry so much about RCS fuel.

The "Probodobodyne OKTO2" will give you the best torque:weight ratio at 12.5 torque per ton (.5 torque per unit) but they'll require some power and will increase your part count to make your ship manuiverable.

The "Mk2 Cockpit" comes in second for T(orque)WR at 10 torque per ton (10 per cockpit).

The "Command Pod Mk1" gives a TWR of only 6.25 per ton at only 5 torque per pod.

I haven't tested but I would think having the torque applied near center of mass would give best results.

You could also try turning on "physical time acceleration" (alt+>) to 2x-3x to make the maneuvering go faster. Just keep an eye on your ship and turn down your time acceleration if you see too much wobble/flexing.

Edited May 16, 2013 by Psycho0124

[Eleven]

For your large ships, try using the RCS parts that only release monopropellant in one direction, you might save some monopropellant with that.

Nice idea, never thought of that!

Pop some empty cockpits or probe cores on that thing. The extra torque will help you turn it and you don't need to worry so much about RCS fuel.

The "Probodobodyne OKTO2" will give you the best torque:weight ratio at 12.5 torque per ton (.5 torque per unit) but they'll require some power and will increase your part count to make your ship manuiverable.

The "Mk2 Cockpit" comes in second for T(orque)WR at 10 torque per ton (10 per cockpit).

The "Command Pod Mk1" gives a TWR of only 6.25 per ton at only 5 torque per pod.

I haven't tested but I would think having the torque applied near center of mass would give best results.

You could also try turning on "physical time acceleration" (alt+>) to 2x-3x to make the maneuvering go faster. Just keep an eye on your ship and turn down your time acceleration if you see too much wobble/flexing.

Another great idea. Never knew about physical time acceleration or adding more command pods.

Edited May 16, 2013 by Eleven

[transcendentape]

The Nova Punch parts pack has 0.5x, 2x, and 3x larger RCS ports for use on ships with widely different masses and also some jumbo size monopropellant tanks. Also, you only need RCS on to change attitude, keeping it on throughout the entire maneuver is a waste. Say you're prograde and want to point retrograde, turn RCS on to start moving, then turn it off. When you start getting close to retrograde, turn RCS back on until you settle into your new attitude and then turn it back off. Mechjeb wastes RCS ridiculously.

[Colonel_Panic]

Hit Alt+F12 and check display control locks to see if there's anything actually locking you out of controlling the ship.

Start your turns to a node earlier, lock on it before you timewarp if you do timewarp, use more RCS positioned further from your moment of inertia, and don't forget to turn it on (default: R). If all else fails, pulse your gimballed engines and use their turning ability to get you started rotating toward the node right before your burn, then peg the engines as you get close to stabilize on the right spot.

[Colonel_Panic]

Here is a SS of one of the ships that just don't like to turn. It has plenty of RCS thrusters and I tried turning RCS on to change from Retrograde to Prograde and it took about 1/4 of my RCS fuel just to do that once. Doesn't seem like that should be the case, how many times do you have to turn your ship just on one mission? Not to mention docking, it would mean that I need to carry as much RCS fuel as I do Rocket fuel.

This second image is when I'm using RCS to make the change from Retrograde to Prograde.

From those pictures I can tell you that you have a HUGE moment of inertia, because the most weight is at both ends. This means that it requires a tremendous amount of force to rotate the ship. Your only recourse is going to be patience. Use a large RCS tank, and use it sparingly. I usually reserve my RCS only for very time sensitive maneuvers, and when I do use it, I pulse it briefly to initiate a slow turn, then pulse it again at the end to stabilize the ship again. If you use it for your whole turn, you'll save only a tiny amount of time over a pulse, but it will waste your fuel quickly.

EDIT: I would also remove the RCS thrusters that are near the middle of the ship. They're not doing any good there and are only wasting fuel. Put them only at the outer corners on the ends to have them be most effective.

Edited May 17, 2013 by Colonel_Panic

[engraverwilliam]

use linear rcs. the four way uses WAY to much fuel