cam following options (solved)

[bambuko]

Simple sketch of cam and a line that is meant to follow it:

cam_sketch.png (7.95 KiB) Viewed 1792 times

Is it possible in FreeCAD?
Converting cam curves to bspline doesn't work because tangent doesn't work?
Any other options?

Code: Select all

OS: elementary OS 6.1 JAlnir (Pantheon/pantheon)
Word size of FreeCAD: 64-bit
Version: 2022.407.26244 +4693 (Git) AppImage
Build type: Release
Branch: LinkDaily
Hash: 9610830a8fd492b3b3d96f8328507c80f1437cda
Python version: 3.9.12
Qt version: 5.12.9
Coin version: 4.0.1
OCC version: 7.5.3
Locale: English/United Kingdom (en_GB)

[chrisb]

Any other options?

Tesselate with multiple arcs to approximate the B-spline you want.

[Roy_043]

Using the BoundBox.Ymin of the cam sketch in an expression can work:

Code: Select all

Sketch.Shape.BoundBox.YMin

See attached file.

[bambuko]

...Tesselate with multiple arcs to approximate the B-spline you want.

Not quite sure how is this supposed to work?
Perhaps I have not explained it well enough....
With multiple arcs you still can only make it tangent to one of these arcs

Using the BoundBox.Ymin of the cam sketch in an expression can work:

Precisely what I had in mind.
Haven't got a clue what BoundBox is
(sorry will have to educate myself, no problem....)
but it works perfectly.
Thank you

[chrisb]

With multiple arcs you still can only make it tangent to one of these arcs

That would indeed require either a complicated cascading expression or some python code. What a hassle compared to the bounding box.

[bambuko]

What a hassle compared to the bounding box.

...

LATER EDIT:
There is a bit of a problem with particular cam I am modelling
or maybe it is something to do with the way I am using it? (inside part design sketch)

Not exactly what I intended....
puzzled

Screenshot from 2022-04-29 18.26.12.png (9.62 KiB) Viewed 1655 times

[chrisb]

Not exactly what I intended....

Looks like the well known flipping. If you want the liine to be always at the bottom, then you must not set the distance between the origin and the line, set instead the vertical distance of one of the endpoints of the line. Those are signed, and thus you can assure with a negative value that it is alway below the x-axis.

[bambuko]

...Looks like the well known flipping...

possibly not???
to be "correct" I would expect

Code: Select all

Sketch.Shape.BoundBox.YMin

to return 14.75
???

Screenshot from 2022-04-29 20.03.24.png (19.89 KiB) Viewed 1593 times

Screenshot from 2022-04-29 20.41.49.png (12.79 KiB) Viewed 1570 times

P.S.
how do you set "vertical distance of one of the endpoints of the line" ??

[Roy_043]

If the cam sketch is not plane-parallel to the XY plane (of the Body) you will need to adjust the expression. The boundingbox of the sketch is not in the coordinate system of the sketch, but in the coordinate system of its container (the Body in your case). If that does not help: post your file.

[bambuko]

If the cam sketch is not plane-parallel to the XY plane (of the Body) you will need to adjust the expression. The boundingbox of the sketch is not in the coordinate system of the sketch...

Thank you!
Looks like you hit the nail on it's head
The sketch plane is in ZY plane (of the Body).
Let's see if I am clever enough to "...adjust the expression..."

LATER EDIT:

bingo

Screenshot from 2022-04-30 08.41.16.png (15.28 KiB) Viewed 1489 times