Making a spiral of catwalks

[John Hepworth]

I'm trying to make a spiral out of a catwalk element.

I'm trying to figure out if there's a way to do this with expressions.

I made a chain, using 

pos=thisComp.layer(index-1).position; [pos[0]+2700,pos[1],pos[2]]

then manually added 20 degrees of y rotation working backwards from the end to the start.

then I parented the layers from the end to the start, and then adjusted the orientation of the start element.

I think what I want is some kind of expression that 

1) moves the layer into position at the end of the chain

2) rotates it 

So is there a way to craft an expression for step 1 than slides the layer into position along the RELATIVE x axis?  i.e given that I want my spiral to rise?

thanks!

John

[Mylenium · Accepted solution]

You would have to convert the coordinates and rotations with toWorld() and toWorldVec() and then calculate the next position. For a helix it may generally be simpler to just use cosine and sine functions and multiply the angles linearly based on index. Could be something like this for the positions:

mSeg=thisComp.layer("Controller").effect("Segments per Round")("Slider");

mInc=thisComp.layer("Controller").effect("Increment per Segment")("Slider");

mRad=thisComp.layer("Controller").effect("Radius")("Slider");

mAng=Math.PI*2%mSeg;

mCen=this comp.layer("Center").transform.position;

X=mCen[0]+Math.cos(mAng)*mRad;

Y=mInc*index-1;

Z=mCen[2]+Math.sin(mAng)*mRad;

[X,Y,Z]

For the rotation you would use the same approach like with that Y position - multiply a fixed value by index. Of course you need to create the controller with the sliders, the center Null and all that.

Mylenium 

[John Hepworth]

Thanks

That may be beyond my pay grade unfortunately... but I'm going to try it...

In the meantime I tried to brute force it.  I can sort of see where the trigonometry comes in as I had to calculate my x and y displacements after positioning the first one manually...

The best I have come up with is to have an original 'neutral' element

duplicate it 

orient it along z 20 degrees (so my catwalks go 'up')

slide it along x 

raise it along y 

then rotate on y so it curves inwards

then repeat with the added step of parenting the previous layers to the 'new' one after I duplicated it and oriented it...

but I'm off to learn how to set up sliders and controllers!  Thanks!

[John Hepworth]

I got part of the way.  At least far enough that the expression didn't have syntax errors... 

I've attached the sequence if you have time to look -- the catwalks are basically just rectangular prisms.

I didn't try the rotation - probably why my catwalks just 'stacked'

thanks again

[Mylenium]

I may be able to set up a demo project tomorrow when I'm back at the computer. On my tablet currently. 🙂

Mylenium 

[John Hepworth]

Thanks again!  

It looks like a VERY elegant approach...that I don't quite understand all the pieces of.

All the best

John

[Mylenium]

Here's a project I hacked together. It should at least give you a grasp of some basics. As usual it could be infinitely refined and adapted to your specific needs and I would try to make it a bit more elegant by auto-calculating the angles and scaling the segments to fit without gaps. Maybe if I have a lazy evening and feel like it.

Mylenium

[John Hepworth]

Maestro!

I'm going to pore over it to see if I can make sense of it - already I was able to semi brute force a result by making a controller with sliders for each segments rotation...while I was still doing the initial position manually, it let me play with the pitch yaw and roll until I got a semi passable result.

But your project is far more interesting...

thanks!

[John Hepworth]

That made me look up how cosine works...which funnily enough has been a semi-goal for awhile "relearn high school math"... oh the rabbit holes these expressions open up!