# How do you create parallel spirals like a rollar coaster track?

I've added a curve spiral with Curve -> Curve Spirals -> Spheric (This might require an add on to be enabled like "more curves"). I'd like to have a second spiral that is parallel to the first to create a spiral track that a vehicle like a roller coaster might ride on.

This is proving to be quite difficult however, since you can't just duplicate and move or scale it since the ends don't line up top and bottom. I'm thinking there's a formula that I need to use to generate the two spirals, perhaps using an XYZ math object or similar.

Here's the top (nicely aligned):

And the bottom (which is not at all aligned):

And the overall shape I'm going for:

As a side issue, the spiral shape also seems to be beveling in a strange way. The bevel object is just a circle (curve) but it deforms into an oval shape that changes axis the whole way down.

## 2 Answers

So, to do what you want to do, instead of duplicating the spiral, why aren't you simply using one unique spiral and give it a bevel object made of several circles (or whatever shape you need to create your tracks)? Don't forget to choose Twisting > Z-Up so that the tracks don't tilt along the curve. If needed, tilt the spiral curve's vertices. It also could be done with an object made of several meshes, following the curve with an Array and a Curve modifier.

I was able to achieve THIS SHAPE with Curve -> Curve Spirals -> Archemedian. I made an initial curve, and then in object mode, I duplicated and scaled it down a few times (scaling a curve does not change it's bevel radius). I gave each curve a bevel radius of 0.02, and manually moved each one along the z axis until the tops were in line. To make the curves look better, I gave them all subdivision surfaces (I could have upped the steps in the curve settings, I just didn't think ahead) See images below:

My Settings for the curve look like this:

I hope this helps you get something more like you want.

• The goal is for the left and right track to stay level with each other all the way down. In other words, the top should like the bottom, but here, the rails are vertical at the bottom and horizontal at the top. – Nick Jun 23 '20 at 6:54
• You can keep them level by excluding the Z-axis (S > shift+z) when you scale. However, the bottoms end up closer together than the tops (don't know hot much this matters). If you want more control, go with moonboots' answer. – Christopher Bennett Jun 23 '20 at 7:06