control rotation animation with single parameter

[jon3de]

Hi,

I have a Null Object with an "Rotator" Tab. There is a float parameter inside. 

Goal is to have the z rotation speed of the helper linked to a single parameter where I can control the "revolutions/Second" of this Null. 

Example:

On Frame 0 parameter is on 0 Null does not rotate.

At Frame 10 to 15 I animate the parameter to 5. The null starts to rotate with the speed of 5 and keeps rotating. 

At Frame 100 to 105 I animate the parameter back to 0. The Null stops rotating and stays at its rotation until I animate the parameter again to a higher number than 0.

 

I hope you get what I want to do. Seems to me a like a nice exercise for houdini but I don´t really get it to work the way I want it to work. 

Any tips or ideas? Thank you. 

Jon

 

 

 

 

 

 

Houdini_rotator.hip

[j00ey]

I would fetch the revolutions per second channel in CHOPs and use an area CHOP to accumulate the animation. Then you can export that to the z rotation parameter [or look it up with an expression]

[jon3de]

wow! Although I´m not sure if I really understand what the "area" CHOP does it works perfect! Thank you for the quick reply Tim. 

Is this somehow correct that the area CHOP calculates the "area" under my revolutions channel graph from frame zero to the actual frame and than uses this area value for the e.g. rotation or any other value ? Pretty awesome

 

[j00ey]

Yes that's right. From the docs :

'Calculates the area under a channel’s graph, which is the same as calculating the integral of a channel, or integrating the channel.'

The slope CHOP does the reverse, they're both very useful.