LightWave - Inverse Kinematics and scissor-lift style landing gear

[FS3D]

Hi all,

I'm getting back into 3D now that I can use LW again. The first thing I want to do is finish work on my Eagle LRF project, and the last few modelling tasks I have are a cockpit interior and the landing gear. I've modelled a basic version in order to get proportions right and to get the IK set up. So far, the forward gear is good to go.

Here's where I am tripping up. In the game (Frontier), the Eagle only has two landing gear pods, each equipped with a scissor-style gear suspension. I am trying to emulate this style. Unfortunately, I'm having trouble getting the mechanism to scissor properly with IK (FK is good for this, but then I lose the ability to use a goal to control the touchdown of the wheels to the floor).

I'll try to post examples later if my connection is restored (I'm having to send this from my iPhone because weather conditions in my country have caused a loss of internet service)... But in the meantime, does anyone have any ideas?

[Rigel]

I can see problems with this setup and IK.

Have you considered doing the whole thing with Cyclist and Cycler?

[FS3D]

I have. I'll try and have another crack at it with Cyclist/Cycler, but I would prefer to be able to control how the wheels react with a floor.

The thought just occurred to me. Is it possible to combine Cycler/Cyclist (on the scissor arms) with a "goal" object that has a limit placed on how far down it can go? I played with an IK Goal object set to use "Same as item" for a child object on the Eagle, set to world, but with a Y position limit that prevented it from going below 1 metre (which in turn prevented the IK rig from going below 1 metre), which achieved the desired effect on the front landing gear...

But if I exchange an IK rig in favour of Cyclist for the rear landing gear, can I achieve the same task for the lower gear?

The only other way I can think of doing this is to combine a cyclist motion for the scissors with an IK rig for a hydraulic suspension on the wheel assemblies themselves.

And if all else fails, I may end up having to re-design the entire landing rig so that I can use an IK solution instead.

[Rigel]

No, cyclist can only be controlled by keyframing the object it is parented to. You would have a null set up so that by rotating the null the gear goes up and down. You control the gear by keyframing that null.

If you're planning to use some form of collision or dynamics, you'll have to find an IK solution. But for a scissors type of movement, that would involve two IK chains crossing each other. I'm not sure how you would keep the cross-over point matched up.

[Gordon Robb]

I'm not sure what you mean by scissor style, but when I dd the gear for the bellflower I animate (FK) the gear being deployed or lowered, which was fed into a null using cyclist. I then used an FK/IK switch to make it IK when down. Then the goal reacted to the ground using an expression which emulated suspension. I hop at all Akers sense.

[FS3D]

Originally Posted by Gordon Robb

I'm not sure what you mean by scissor style, but when I dd the gear for the bellflower I animate (FK) the gear being deployed or lowered, which was fed into a null using cyclist. I then used an FK/IK switch to make it IK when down. Then the goal reacted to the ground using an expression which emulated suspension. I hop at all Akers sense.

I have tried a few ideas out, but in the process of redesigning my rig to implement these ideas, I managed to crash LW and lose my work (I haven't gotten back into the habit of saving my work often like I used to, so several hours of modelling went down the drain)...

As an interim, I'm going to try out the idea of telescopic landing gear suspension. That's easier from an IK point of view, and I'll see how it works out.

The next idea is to try tire deforms on a hard surface. That's a refinement I might not need yet though.

[3D_CG]

set lightwave to save every 5 to 15 minutes....
its a pain but worth it...

I tell Lightwave to save every hour ok... but it saves every 10 minutes... cant figure that one out, lightwave cant tell time I guess..

[ccclarke]

I've built lots of scissors-lift mechanisms for jobs using different techniques. The best is usually what works and meets deadline.

You can apply bones and weight maps. Cyclist is good. And morphs work well too. For a landing gear, the Morph Mixer slider control does a good job of imparting the impression of heavy weight if animated properly.

CCC

[FS3D]

Originally Posted by ccclarke

I've built lots of scissors-lift mechanisms for jobs using different techniques. The best is usually what works and meets deadline.

You can apply bones and weight maps. Cyclist is good. And morphs work well too. For a landing gear, the Morph Mixer slider control does a good job of imparting the impression of heavy weight if animated properly.

CCC

Thanks for the suggestion. I'm not sure morph mixer is the way to go, since morph transitions tend to move the points in a straight line between the morphs, which is no good for rotations unless you're only talking about two or three degrees.

Cyclist might have been the way to go, though TBH I've implemented a telescopic landing gear rig now (which MM would work well for, but then again so does IK), and it appears to work well for the landing gear so I may stick with it and detail up the rig. The IK on it has so far worked in all my tests (except it may not work if the craft was tipped to one side, but that's because of the angle of the wheels and not a fault of the IK rig itself).

The next task is getting the wheels to rotate based on the amount of distance covered on the ground, but to do so only when the wheels touch down. I might just have to animate them using keyframes and a null object.