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Stuggz

Simulation problem with several hinges!

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Hi there, relative noob here.

 

I'm trying to build the moving parts of a construction crane that's moving a girder, like the attached diagram. The top block should be slowly moving left to right, and the girder at the bottom moves a bit behind it, the top bit stops and the girder slowly swings to a halt underneath. The strings can be rigid, they simply pivot.

 

In my mind it made sense to use a set of four hinges (i only need the objects to swing in one dimension) but for the life of me can't get it even close to working! I got some success with a basic arrangement swinging very light and bouncy, but as soon as I made the girder have a bigger mass the hinges seemed to stretch, gaps appeared everywhere, and things refused to swing how I wanted them to...

 

How would you experienced guys go about doing this? How would the parenting work? Which bits would have dynamics tags, all of them?

 

Thanks for any help you can give!

 

S

 

pendulum_trim_00000.thumb.jpg.b8eeb158a6cd78cbc7b33266d3bae174.jpg

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On your dynamic connectors (Hinge) turn the bounce down, but more importantly, Go into your project settings (Ctrl D) > Dynamics tab > Expert tab, then double the steps per frame and Maximum Solver iterations per step. Hope this helps.

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Does it have to be dynamic ? You could fake it with an XPresso memory node. In this file the lower girder X position is 15F behind the top one.

 

IRL the lower girder would rise slightly when the top moves - to keep the chains a constant length.

 

fake.c4d

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  • Thanks both!

    I sort of made progress with it - the project settings helped to a decent extent but hinges are still stretchy if pushed! I think I could get away with it as long as i keep everything slow so it's not noticeable... Hinge bounce has always been at zero.

     

    I think I may well end up faking it TBH as the hinges are being such a pain! 

     

    I've attached the project file as far as I've taken it, if it interests you.

    pendulum test v2.c4d

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    You could try some keyframed damping on the girder at the end of the movement (dynamics tag, force) - a bit like this

     

    damped.c4d

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  • Cool, yeah I'll try that too. Cheers Jed!

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    Here I used your scene and some Pythagoras to fake girder Y movement in my original XPresso fake

     

    fake2.c4d

     

    AFAIK it takes a lot of skill for a real crane driver to move a load and stop it dead without swinging

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  • 1 minute ago, jed said:

    AFAIK it takes a lot of skill for a real crane driver to move a load and stop it dead without swinging

     

    ...yeah I wanted to keep the swing, hence the hinges - the stretchiness I was talking about was the objects twanging further apart from each other, like they were hung from rubber bands!

     

    Thanks for your help anyway, I'll check out the pythagoras thing in a moment.

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