Jump to content

Gimbaled Engines+Stabiliser Nacelles(Breaking Ground) - Allows 160t ship to land and manoeuver without RCS


Recommended Posts

Welcome Humans,

Here I explain the secrets of how to construct gimbaled engines and maneuvering nacelles, which allow high performance in large craft.

Here is an example of an otherwise unremarkable large craft with Gimbaled engines and Stabilizer/Maneuvering nacelles :

083BE3A09DCD60344A3B43CA4F0549EF376B07B8                                                                                                                                                                                                                                                                              

1. Gimbaled Engines

These allow landing without RCS of any kind.

In practice the gimbaled engines worked far better than I initially expected they would.  They are superb for arresting horizontal velocity during descent and make RCS un-necessary, for a ship of this size it means no vernier engines and thence no oxidizer needed.  I suspect that even with engines that possess their own gimbals disabling them and using something like this will have many use cases.

1E20CEFE96A403E5D8402BDA55EE938C4EF35460EE14DBBB4D3BA92ACB5CD93800A2D7EE620667FE

Whole engine assembly is free to move on its own axis.  There are 2 rotators at the back attached to the fuselage.  The rotator connected directly to the fuselage controls the movement of the engine block as a whole and can rotate it though any angle.
The rotator connected to next to that is part of the gimbal mechanism and is for the U/D(Y) translation.  At the end furthest from the fuselage there is an octagonal strut.  This is connected to the main body of the fuselage with 6 struts. This gives essential structural support to the whole assembly.  Connected to this octagonal strut is another rotator.  This has no motor and is free to rotate.  It's function is part to impart stability to the assembly.  The nuclear engines are connected to each other in the U/D(Y) translation axis with fixed struts as they will always maintain their relative position.

5A8CFADA60546C41DBAC2C97208BEC6BB0CC96995230D369DFF6690DD7346530C4BDC7219343EABC

Hinged struts connect the engines in the L/R(X) translation axis.  This again is for stability of the assembly and to ensure the engines always retain their relative position.  Otherwise each engine is connected to the assembly with a rotator which moves it in this axis.

 

2. Stabiliser Nacelles

Example below of flying this ship 160t, handles like a fighter, and definitely a lot better than Imperial Cutter in Elite.

*** Please watch video below on Reaction Wheel Performance where it has been tested - reaction wheel placement may not have such a big effect as it seems -- more testing is needed at this time -- it may be weight distribution and structural stability that gives the feel of higher performance than extended reaction wheels ***

Experiments and Advice seems to show that reaction wheel placement does not work as one would expect and it does not matter where on the craft reaction wheels are placed.  Results below are likely due to the weight balance of the craft/vs testing reaction wheels in center and not due to reaction wheel placement.

I have demonstrated in below video.

Other purpose of these stabilisers is to allow the craft to land by supporting the main body and preventing roll over as well as distributing weight.  In this instance they may also be retracted for placement in the initial launch faring.

 

For those who know, will and dare to do so the craft may be downloaded https://kerbalx.com/gavin786/Excursion3-export

Gavin786

 

Testing of Reaction Wheel Placement

I decided to make a test of Reaction Wheel placement.  Results are mixed bag.  For this model there was only a 10%(Well within margin of error) difference in 360 deg turn time.  Again it did seem the 2nd model was massively more stable than first where I couldnt line it up easily at all.

 

Edited by Gavin786
Link to comment
Share on other sites

5 hours ago, Gavin786 said:

Having the reaction wheels away from the main body of the craft maximizes the torq they can produce on the body -> substantially better maneuverability than if they were at the center of gravity.

How certain are you about this? AFAIAA, reaction wheels produce fixed torque rather than fixed force. Length of lever arm shouldn't matter.

Link to comment
Share on other sites

21 hours ago, SchweinAero said:

How certain are you about this? AFAIAA, reaction wheels produce fixed torque rather than fixed force. Length of lever arm shouldn't matter.

I am not sure about it as I said I need to run the numbers and test it out.  Its subjective experience right now.  I maybe aught not to have advertised it so strongly until I fully did the experiments.  I did compare it by putting the same number of wheels at the center of the ship and there was a difference but this could be due to weight distribution rather than increased torq.  Initially I place RCS(vernier) at the ends of the nacelles and that for sure 100% made a difference.  It is a natural assumption that the reaction wheels obey the same laws of physics but if they dont then well...

I recently made a air vehicle based upon a similar principal and I didnt get nearly as much of a torq advantage as I thought by replacing 1 large reaction wheel in the center by small ones on the thrusters.

938BF67901D492E05FD770C9105B1475B6897DB4

Edited by Gavin786
Link to comment
Share on other sites

2 hours ago, Shamux said:

Are the engine gimbals controlled by IJKL or are they directly bound to WASD? Speaking of which, it would be very useful if robotic parts bound to rotation keys returned to center.

Engine gimbals are bound to the translation axis that are normally used for RCS.  I used the U/D and L/R in this case as its bound to the analog stick on my flight controls but you can bind in your own designs to as you like.  To bind a rotator to an axis there is a menu option on the top left 'action groups' and there are a number of options(added for breaking ground) to bind axes to the robotic controls.  First thing I did when I started KSP was rebind all the controls so I have no idea what the "proper" control scheme is.  I would hazard a guess that it is the IJKL.

As far as returning to center goes, it is totally NOT obvious and I did even a video about this but there is an option there(very tiny) just under the bound control to change mode between relative and absolute.  Grab yourself a magnifying glass and see if you can find it .  Try changing to absolute and see if that helps.  

Gavin786

Link to comment
Share on other sites

23 hours ago, SchweinAero said:

How certain are you about this? AFAIAA, reaction wheels produce fixed torque rather than fixed force. Length of lever arm shouldn't matter.

I amended the above post with a test I did and result is a mixed bag, def not as big a difference as I had hoped.

Question really becomes : does it genuinely not matter WHERE on a ship a reaction wheel is but it will act the same way, even if placed in really weird places it just doesnt matter(unlike RCS) ?

Link to comment
Share on other sites

I'm fairly certain that the reaction wheel placement doesn't matter. What does matter is that the wheels are fixed in place properly with struts or autostruts if you have a large stack. If your stack is only attached at one end, the other end will flex and lose energy before it affects the rest of the craft. In extreme cases part of the stack will break off.

Link to comment
Share on other sites

On 6/27/2019 at 9:16 AM, Gavin786 said:

Having the reaction wheels away from the main body of the craft maximizes the torq they can produce on the body -> substantially better maneuverability than if they were at the center of gravity

Actually, this is incorrect.  Reactionwheels will do the same action on a craft no matter where they are.  

Link to comment
Share on other sites

7 hours ago, linuxgurugamer said:

Actually, this is incorrect.  Reactionwheels will do the same action on a craft no matter where they are.  

I already amended the above and did a video to test it out.  Well within the margin of error and not a big change as one would expect so I assume you are correct.

 

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...