Repeating part at odd intervals along spline

tony_459

I'm modeling a roller coaster and have a number of parts that I need to repeat some fifty times. Trouble is.. the pattern is not at regular intervals along a symmetrical path but at odd intervals along an arbitrary spline and at varying angles (tangent to the track). I haven't seen a feature in Onshape that allows me to do exactly this so I'm exploring partial suggestions that simplify the task as much as possible. Or maybe there is a feature made just for this and I missed it?

My best idea at this point is to use a regular pattern along a spline to quickly create the right number of part copies and then to transform each individually---meaning to translate and rotate each. It's better than nothing but it will take a while to do. Better ideas would be much appreciated. Thanks to anyone who can at least point me in the right direction!

For reference:

https://cad.onshape.com/documents/7a718b6d8bf3b9c0547e6d8c/w/c80e2acd2d7ab0fa4ec09ecf/e/a20b204b5215556313cc2853

You'll notice in that link (a frozen snapshot of the model as it is now) that the columns don't quite touch the spline that now stands for the track. My goal is to add the connection plates at spline level and to then fill the gap between the plates and the columns underneath them. The spacing between columns is variable (to my surprise, but that is how this particular coaster was designed, it seems, without regular patterns).

konstantin_shiriazdanov

it is not a good idea to make part patterns in part studio, but at least what parameters you use to define orientation except the path itself?

tony_459

Hi Konstantin,

I have to admit I don't know exactly how to define the orientation for each part. I could use a transform, but then I would have to numerically specify the rotation angle---it would take a while to do.

I would much prefer to avoid part patterns---I've done them before only to have Onshape slow to a crawl---but sadly I need the connection plates to be in the same part geometry as the columns and the plane on which those stand. I intend to export the parts for simulation and for that the fewer the parts the better.

Any advice welcome!

konstantin_shiriazdanov

I can offer you to rule plates origin position by length along the line of path projection on the land surface, it seems a resonable first step. Second step - define plates orientation - the best would be to use the tangent line to the path projection on the land surface, the third parameter is the distance between the plates - also some numeric array intended. If it suits you we need a combination of Parameter pattern FS which already exist, and some FS for body transform along the path (using line to line transform among the path tangents) based on the length parameter.
In this document you can find some combinations of parameter pattern, and transform by path features:
https://cad.onshape.com/documents/24d450db10d7bd8a5642da38/w/83ada25ced2e1aacb278f760/e/92624af0f11c97446446a43e

tony_459

That might work! This won't be the last time I'll run into this problem, so if I can find feature scripts for the patterning, I'll have picked up something valuable for the future. I'll run a search but if you have the link or name handy for the feature script you mentioned could you share it? Thanks again!

konstantin_shiriazdanov

check the link, I've edited the comment

tony_459

Konstantin, that FS is exactly what I hoped but didn't expect to find. I still have to try it, but if it works as I think it does, I will have good uses for it. Question: Why would something like this stay as FS and not become an official feature? The ability to create irregular patterns would be a great complement to the linear and circular and regular spline patterns we can do from the toolstrip. Thanks again!

tony_459

Question: The path along which I want to pattern is a 3D curve. I can get the separation distances between parts in 2D sketches using the Dimension tool, but... I don't know how to do this in 3D. Konstantin, how would you approach this? Is there a way to get 3D distances between points, and can I get the full lengths of a curve segment (as opposed to just the straight-line distance between its end points)? Sorry for the many questions! 

konstantin_shiriazdanov

As I proposed, i would make a projection of the path on the horizontal plane and used the projection curve as reference for patterning

tony_459

I got it to work! Thank you!