How to model a marble track?

øyvind_kaurstad

While the subject is rather specific, the question is perhaps a bit more generic. Suppose one wants to model a pipe or a half-pipe (or a winding road for that matter) that starts somewhere up in the air (bear with me on this), and has a downward slope towards the ground (or just a plane), while at the same time taking turns, perhaps crossing under itself on the way down.

While I realize that Onshape (or other MCAD systems) might not be the tool for something like this, I think it should be possible to do it. I have some ideas, and I have done some testing (not yet with a satisfactory result), so I'm asking for ideas on how to best try modelling something like this.

_Ðave_

I suppose it would be best to wait for 3d sketching capabilities.

øyvind_kaurstad

Hmm, ok. Do we know if and when Onshape might have that?

Stuart_Tod

Not just 3-d sketching - but a path mate! Have been asking for this for a while...

michał_1

First attempt:
https://cad.onshape.com/documents/f31b831a0519fa0b5ec95839/w/ffe9d6810c4039240d92c591/e/755240a0eded28c3b9e9a6a0

øyvind_kaurstad

@michał_1 Some interesting techniques there, and quite a lot going on. I've looked at it, and you did some things there that I hadn't thought of. And you reminded me that I need to get accustomed to use a bit more of the available tools in Onshape, especially 'Shell' and 'Thicken'. I keep forgetting about those, but they certainly are very useful sometimes.

Thank you very much for taking the time to do that!

øyvind_kaurstad

And many, many hours later, this is what I ended up with in Onshape:


And then, some more hours later, this is what I got from my 3D-printer:



This was not easy to model, I'll admit. However, I did learn quite a bit, and I would probably be able to do it slightly faster were I to do it again. Which isn't entirely out of the question.  :-)

robert_hercules

That looks like a very nice marble maze...but do we have any way to model the marbles following the path yet, or is that still an OnShape non-starter?

jeff_mcclain

Ohhhh….very interested in this. I've been trying to figure out how to define a helix or path and then have a sketch of a half pipe cross section swept through that path, which is pretty easy, but I want to be able to have it "rotate" as it goes to stay pointed toward the normal of the curve. This would allow the half pipe to rotate to oppose the curved path wanting to fling the marble out. But I don't know how to define that and have not yet been able to sweep a sketch (screw patterns like a helix are easy, but how to have it rotate the sketch at the same time)?

jelte_steur814

Hi @jeff_mcclain,
"pointed to the normal of the curve" might not be mathematically correct. imagine a strainght line with an arc element after it, the normal of the curve of the line is a full plane, so not fully defined. while the normal direction of the arc isn't actually helpfull in keeping the marble in, since it would keep the track flat.

I think the implicit math of the curves isn't goint to help you here. Perhaps the new 'Routing curve' feature (link below) may help. It requires some more manual inputs but it works.

Create the first curve to represent the marble track nominal position, and a second one with manual offsets in the curves to determine the direction.
Then loft a face between the two routing curves to create surface that defines the perpendicular direction, and a sweep with 'lock profile face' option.

I tried this way of working and it seems to work…

marble track experiment

https://cad.onshape.com/documents/bd7be0eed8222d8883d87406/w/206de415247c061ce4959c3c/e/b01c59d857f572fa2b834b21?renderMode=0&uiState=66d6da5e17ff872f8c5e4b93

new curve features forum thread:
https://forum.onshape.com/discussion/24874/routing-curve-control-point-curve-introduction-of-two-new-features-for-3d-curve-creation

jeff_mcclain

Thank you! I will play with this! I suppose I meant "a normal line to the plane that slices the conduit/curve".