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Parent local axis constraint?

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I'm currently rigging the internals of a traditional engine, and I'm a bit stuck.

I have the main crank rotating, the connecting rod attached with a look-at constraint towards the piston. The piston only moves up and down in the Y-axis. So far I've done a Parent Blend constraint from the Piston to the connecting rod, masking everything but TY. But it's using world Y axis. If I go and rotate the engine at the object level, the rig breaks. The piston does not translate to the new local Y axis. I'm very new to Houdini rigging, so I'm just wondering either how I can set it to use local axis constraints, or what other ways I can/should solve this?


Edited by Tronotrond

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Was able to solve this in the end. Had to modify the constraint CHOP a bit; Use constraint get local space, blend the parent movement, then add in world space position at the end. Seems to be working!

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And no.. I thought it was fixed, but it wasn't..

I recreated my setup in a simplified scene. Would any experts mind taking a look? I would be forever grateful :)
I should think this is a very simple setup, but I'm definitively having some problems wrapping my head around CHOPS still. The rig is fine as long as the "engine object" itself is not rotated in any way. But once rotated things explode. I believe my problem is that I cannot link the piston to the piston arm directly without getting a dependency loop from the LookAt constraint. And then in CHOPS having the piston itself just follow the Local Y-axis of the piston arm. Works fine in world space, but once things are rotated things are not so happy anymore..



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2 hours ago, Paulx3d said:

Hi @Tronotrond! I face the same issue as you. Do you managed to solve it ? and how ? 

Back then I did unfortunately not. I worked around it by avoiding rotating the model.
Now that I'm a little older and hopefully a tiny bit wiser, I'm thinking you might have to reference and do some matrix multiplication of the object base rotation to make it work, but on top of my head I don't know how :)

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