Gimbles - Not sure what they do!

[dpraptor]

Hi,

I see the gimble settings on rockets - and read about people turning them off or on, but I have no clue why or when you would want to do that! I read about them in the Wiki, so I understand what they are, but can someone update me on how to use them, or when to? I searched the forum but could find nothing to explain their use.

Thanks!

[Xaiier]

On-if you need to turn/other controls aren't enough

Off-if they are shaking your rocket apart/other controls are enough

EDIT: @ people below did you even read his post? He knows what they are, he's asking how/when to use them...

Edited July 11, 2013 by Xaiier

[Sathurn]

This is a joint that allows the thrust of the rocket to be turn to the side (just a little bit). Thus allowing your rocket to be turned.

However the ASAS pre .21 over correct shaking your rocket to pieces.

The video on he .21 development gives me great hope this will no-longer be a problem.

[regex]

If you have, for instance, five Mainsails (four on booster stages and one in the middle) it is often beneficial to shut off the gimballing on the outer four engines in order to prevent your rocket from shaking too much. Basically you want to shut off gimballing on an engine when it would be over-correcting too much. 0.21 will probably alleviate that problem entirely.

[FITorion]

They allow the engine to move a few degrees off straight down... like thrust vectoring on a jet engine. It helps steer the rocket... but it has a lot of power in steering the rocket. So if you have a lot of engines and all have their gimbles on then it's hard to make small corrections... They invariably become LARGE corrections. People turn some off so they can pilot more smoothly.

[SkyHook]

Engine gimbals allow you to control the direction of thrust of some engines, effectively allowing you to control the direction of the rocket while in flight. When ASAS or many mechjeb features are activated, the flight computer will use the engine gimbal to control your craft. Hope this helps!

[Gobbles Gusto]

If you have, for instance, five Mainsails (four on booster stages and one in the middle) it is often beneficial to shut off the gimballing on the outer four engines in order to prevent your rocket from shaking too much. Basically you want to shut off gimballing on an engine when it would be over-correcting too much. 0.21 will probably alleviate that problem entirely.

This......

[stupid_chris]

Gimbals are modules on rocket nozzles that orient the exhaust in different directions. Basically, it moves the thrust of your rocket in a way to turn your craft around. It's a form of steering. The biger the angle at which the nozzle can gimbal, the more it can "steer".

People are often turning it off on outer boosters because of two reasons:

First, there's only two values for the gimbal: "yes" and "no". This means, either it's turned to the max, either it isn't at all. This makes the controls a bit too reactive often and that isn't always appreciated by your rocket.

Second, the current ASAS system oversteers a lot, and with that yes/no system, it's kinda destructive. Disabling the gimbal locks the nozzle in place and allows for smoother controls.

This might change in the near future with the new ASAS probably coming with .21.

[Eric S]

Off-if they are shaking your rocket apart/other controls are enough

Also off if the engines are located above the ships center of mass, since the gimballing code doesn't take that into consideration, resulting in the higher gimballed engines fighting against the rest of the craft's control authority.

[dpraptor]

Ahh - I see - I do build a lot of rockets that would fall into the "I need to turn the gimbals off on at least 10 of these engines!!!!" catagory, so thank you all for your great insights and help! I will be experimenting with this!

[Tiron]

Also off if the engines are located above the ships center of mass, since the gimballing code doesn't take that into consideration, resulting in the higher gimballed engines fighting against the rest of the craft's control authority.

That's because it moves them all in concert, which is really weird looking when you watch it. This also means you can't use gimbals to control roll at present, which isn't strictly accurate.

But yeah, this is mostly a thing with mainsails, which are so powerful that they can literally tear a rocket apart with their control forces.

[NeoMorph]

The easiest way to explain it is if you have a go cart and four people to push. If you have one person steering the cart goes in the right direction. If everyone has a steering wheel for their own wheel then it gets wobbly as heck as the cart can end up steering against itself. Basically limiting the steering to one person steering stops the shake, rattle and roll.

I've got one rocket that works perfect with the outer engine gimbals turned off but if I leave them on the boosters fall off and everything goes KABOOOOOOM. Another rocket I have to turn the gimbals off until 20km and then turn them back on to help with the gravity turn. It would be nice to have a programmable flight path to enable/disable things like gimbals. There are too few action groups at the moment.

[FortyCaliber]

Gimbal*

Tech Descriptions of Gimbals:

http://en.wikipedia.org/wiki/Gimbal

http://en.wikipedia.org/wiki/Gimbal_lock

Pictures of Gimbals in real life:

http://www.pilotfriend.com/training/flight_training/rotary/images/9.jpg

http://cache.gawkerassets.com/assets/images/lifehacker/2009/07/diy_steadicam.jpg

http://www.pjentertainments.co.uk/new_images/3_ring_gyroscope1.jpg

http://craphound.com/images/toddlergyrodish.jpg

[dpraptor]

Wow - I see! That may explain why some rockets I have launched wobble a lot or explode on takeoff or in mid flight. I tried turning gimbles off on 4 of an 8 engine cluster, and I noticed there was less wobble. Originally, the rocket did explode a few times during test launches, but after I turned the gimbles off on half the engines, the flights were flawless getting into orbit.

Thanks everyone for your help!