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How to accomplish physically linking CAD objects
I am being asked to do something I haven’t messed with before, so I’m pretty keen on giving it a go. I will be getting some CAD’s of a grass mowing unit, and need to animate the way it interacts with the ground, moving up and down as the ground moves. More specifically-
Think of an old fashioned reel mower suspended by a short arm that hangs off a tractor. as the tractor moves forward, the reel mowing unit follows the ground contours via a ball joint at where the unit is hanging off the arm, and another where the arm meets the tractor.
Is there a way to connect these objects so that when I move one, the others move in kind? What would I use, bones? Rigid body tags? Or would this be a good excuse to upgrade to R12 for the hinges and connectors features? Or will this just take some trickery in the animation process?
I was hoping I could link all the objects together, toss a rigid body tag on the ground object and just animate the tractor moving and have the mowing unit automatically follow the ground contours. Am I dreaming?
Thanks all for the advice in the past on this forum, its really helped me out of some deep holes!
Matt
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2 Replies
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Lots of ways to do it. But you have different issues.
How to make the unit – You could go the character route with bones, joints, etc. In R12 you could make motors and hinges, etc. You could go with all rigid subcomponents. It may be easiest to simply parent subcomponents to systems and keyframe their motion with a little restriction of movement with xpresso (when arm position changes, unit position changes; if arm rotation changes, unit rotation doesn’t, until it reaches a certain limit, then it rotates; etc).
How to make the unit move – In R12 you could put a motor on it, but just keyframing it along a spline is probably cheaper than upgrading.
How to make the unit move along the ground – As long as you’re moving along a spline you could adjust it so it’s always above the ground in appearance. Or you could put rigid tags on the ground and object.
Whichever way you go, you’re in for a lot of experimentation. It doesn’t need to be a full physics simulation like it would if it was a video game. If you’re only making an animation, than cut corners and bake it in so it looks real without needing to design the laws of physics.
Cory
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Cory Petkovsek
Corporate Video
http://www.CorporateVideoSD.com -
Thanks for the perspective. I did realise there would be many ways of doing this. I’m trying to get my hands on the CADs before I promise too much, so hopefully that will happen in the next week or so. I don’t want to promise too much before seeing the assets that they give me to work with.
I think the animation along a spline will be the easiest way to go. You’re right, i don’t want to redefine the laws of physics for this. there are 3 or 4 major components that all move to make this thing follow the ground, so I would like to make the subs assy’s and see if I can control them enough just my animating the assemblies. That would be easiest and most understandable to me. I do know some expresso, so I can utilize that if need be. This thread will be alive for a while, I’ll try to post WIP’s and most likely more questions along the way, so others can search and read about it as well.
Thanks for the advice!
Matt
Its more fun to ride a slow motorcycle fast than a fast motorcycle slow…
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