gimbals and transforms

[numerobis]

I decided I'm sick of gimbals going the wrong way on a Goddard-style rocket, and not dealing with roll, so I'm working on a smarter gimbal module. Only slight issue: I'm not entirely clear on exactly how to tell KSP to point the engine appropriately once I've calculated which way it should point.

So far what I've done is copied the LV-T45 and changed "ModuleGimbal" to "ModuleSmartGimbal".

I was assuming that inside that module, what I should do is find the gimbalTransformName transform and make its localRotation point according to what my math says it should point.

Here is what happens when the gimbals point at Euler angles (0,0,0), which I assumed was the neutral position:

So I am definitely setting the local rotation: the engines are pointing opposite each other, as you'd expect on a symmetric craft. When I apply pitch or yaw, they move accordingly (I haven't implemented roll yet). But (0,0,0) is not the rest pose. Am I changing the right transform? Or is the rest pose something else?

[Echo 8 ÉRÀ]

Why not just do the simple thing and record the initial transform as the rest pose? After all, it makes the code a bit more robust in the case where the modeler didn't make their rest position a simple 〈100〉 direction.

[EndlessWaves]

Yeah, that's how the stock gimbal module works. Store the initial rotation and then each frame set the rotation to that plus maximum_gimbal * control_input (the latter being -1 to 1).

[numerobis]

Crazy talk -- that idea is way too simple.

Thanks all!

[numerobis]

Anyone want to test ModuleSMRTGimbal?

Usage: first, build. You'll need to edit the references to point to the appropriate place, and you might want to update my after-build custom step.

Afterwards, in any part.cfg, replace ModuleGimbal with ModuleSMRTGimbal.

Now you can fly rockets like this one (well, for the most part -- when the center of mass flips from being below to being above the T45s at the top, you lose control for a little bit):

[Faark]

Nice, so i can soon use my abandoned "Lander with engines on top and bottom" designs, again? And is it safe&stable enough to use this Module for all Engines? I don't really like editing those configs and would prefer to replace the stock gimbal modules after loading the parts. I wonder if it is even possible to make the save file compatible.

ps: What about using the stock ModuleGimbal as base class? That way it might only be necessary to overwrite OnFixedUpdate and let the stock code handle everything else.

Edited August 13, 2013 by Faark

[numerobis]

Why not subclass is that there's too little worth reusing.

It should be equally safe for use on any engine. Your action groups to toggle the gimbals aren't likely to work out of the box, but other than that it's a drop-in replacement.

It isn't 100% for me in testing last night though. Sometimes it seems to reverse the controls. It'll be a few days before I can debug it.