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Parallel only in workplane? (by Jag)
I'm trying to make a 4-arm bar linkage... with another 4-arm bar connected to it beside it (same 4-arm system, tilted towards each other at the top)

There are multiple issues when trying to handle this.
1. Parallel constraint of one of its base lines and the axis: Am I correct in that the parallel constraint only works in a single plane?
2. Though I began and switched immediately to working in 3-space, all my lines went into a plane anyway: I guess this is okay?
3. Once I get 1 to work, we'll see what else I encounter! :)

Thanks.
(no subject) (by Andrew)
You can use parallel in 3d space, and if it causes an error, you have conflicting constraints.

Switch your lines to construction [g] and the not all points co-planar is eliminated. shift s allows direct drawing of construction lines.
Sun Jun 6 2021, 12:03:46
(no subject) (by Paul)
Parallel constraints can work in 2D or 3D. Just to verify I make a line in-plane and then switched to sketching in 3d (same group) and was able to constrain 2d line and a 3d line to be parallel. The 2D one stays in the plane as things are dragged and the 3d one is allowed to go anywhere but will stay parallel to the other. So no problem there.

I would make one of your linkages first as a 2D sketch. It should have 1 degree of freedom indicated in the text window. Then switch to sketching in 3D and build the other one. It's not clear to me how your model was meant to move, so I wasn't able to figure out what's wrong. One problem seemed to be trying to make a rigid rectangle in 3D as part of the mechanism, is that correct? I can't figure out how to do that well in that sketch. Using 1 parallel and 2 perpendicular constraints seem to work. Adding 2 lengths yeild a rigid rectangle in 3D with 6 degrees of freedom (3 position and 3 orientation).

It seems to be a problem of selecting the correct set of constraints for what you want. Build it up slowly and make sure it's as constrained as possible as each piece is added.

On a related note. One thing I'd like in the future is the ability to make assemblies with multiple parts linked in a single group. That way you could design 3D parts separately and build a linkage by constraining them together.
Sun Jun 6 2021, 12:30:29
(no subject) (by Paul)
Andrew,

You wrote that "shift s allows direct drawing of construction lines." not sure if you're aware but now you can also start a line segment and press "g" to toggle it from normal to construction while it's being drawn. I think this was part of the 3.0 release.
Sun Jun 6 2021, 12:34:15
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