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FSXA Animating a roller chain

Vitus

Vitus

Resource contributor
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newzealand
Good Morvening everyone,

I am currently working on the emergency gear which is operated by a roller chain. I created the chain out of many copies (to element) of some simple boxes and applied a skin modifier to it using a bone object for each link. It is not mapped and textured yet, but to give you an idea, it looks like that right now:
chainjlf.jpg


I am struggling a little bit about the animation. I started with position-animate the lowest-left bone (which was the first bone placed) and moved it to the position where it will be at keyframe 100. Next, I tried to apply rotation-animation to each link to move the chain around the wheel but its a pain in the ass because modifying say a chain link at keyframe 20 will mess up keyframes 1 to 19. Hence I would end up readjusting every bones' rotation for every single keyframe - and there are 82 bones in the scene right now!

Before I am doing such a silly thing, I better ask you guys if anyone has an idea of how to improve that method. I saw the chain in the Hughes H-1 aircraft and I know that some months ago the creator was around in this forum ;).

Looking forward to hearing your ideas!
Vitus
 
Man, if you can get this to work, it will be a great feat of engineering, Vitus!

Only FS2004's SDK allowed for this (the drive chains on the Wright Flyer). But FSX no longer supported the animation system.


Good luck Sir!



Bill
 
Thanks for your replies! In the meanwhile I found out that the exporter has some problems when you cascade the hierarchy too much. And over 80 bones where too much for that. Therefore I started again with a different approach that works pretty good. Needs some tweaking though but for now its alright.

It works like this:
- I modeled each chain separately and at first linked one after the other. Please note that if you try to open the "Select by Name" dialog box with "Display subtrees" activated, GMax will crash.
- I rotated the chain links around the pinion (is that the right word for it?) with 10 degree steps for each link.
- I set the animation for the lowest link - which is the highest in the hierarchy. I defined frames 0 and 10 and animate-moved it in a way that its pivot positions at the place where the pivot of the second-lower (in terms of hierarchy) link was located. 'Hope you understand what I mean ;)
That gives me a defined movement which is imho the better way than trial-and-error.
- I added a new key at frame 9 and adjusted the velocity settings of the keyframe for a constant motion. After that I deleted keyframe 10 and copied keyframe 0 to this position. I changed the velocity settings for the new key 10 animation to a step.
- I copy & pasted the keyframes until frame 100 was reached.

With these setting the roller chain behaves as follows: it smoothly moves up between keyframe 0 and 9 and then jumps back to its original position. But as the ends of the chain disappear in the floor of the cockpit, it seems like the chain is moving constantly upwards.

Because I just moved the chain by the length of two links, I only have to animate four links for the rotation around the wheel (two links left, two links right of it).

- For keyframes 0 to 5 I animated the first chain link to rotate -10 degrees. I added a key with no motion at 9 and copied keyframe 0 to frame 10.
- For keyframes 5 to 10 I animated the second link to rotate -10 degrees and as above, added a key at frame 9, deleted 10 and replaced it by a copy of keyframe 0.
- As above, I copy & pasted these keyframes until frame 100.
- I used the same method but with +10 degrees for the two chain links right of the wheel (the downward side).

- To get again access to the "Select by Name" dialog, I linked all the "upward" chains (left side) that have no animation attached to the first chain (with the position-animation).
- I linked all the chains on the wheel that have no animation attached to the second upward-rotating-animated-chain-link.
- I linked all the "downward" chains (right side) to the second downward-rotation-animation-chain-link.

Doing that, the hierarchy becomes very flat again and neither the exporter, nor the "Select by name" dialog are upset with you.


It sounds difficult. It is difficult. But it finally works.


I just have one problem with the rotation animation. How do I have to change the velocity settings of the keys to get a "step" animation like in the position-animation? It seems like the chain is moving slightly up and down because it doesn't perform the "jump" needed for a smooth animation.

Thats all. Have fun trying it yourself ;)

Vitus
 
I added a texture to the chains and now it looks like this:
chain2m.jpg
 
Mapping finished, raw texture finished.

chain3.jpg



I don't know what you guys think... I LOVE IT! :ziplip:
 
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