Hi, I wanted to animate a point moving on a zig-zag path at constant speed and later attach a line (with 2 points) to that animated point to simulate an antenna of a car.

The main problem is the animation of the point following the path. I can see the velocity is a bit chaotic. It's not much but when I simulate the antenna, it's super obvious. To give an exemple here are velocities 3 frames in a row:
f66 v13.8136
f67 v14.0461
f68 v13.5684

To make the point animation, I did these steps:
1. create a zig-zag curve
2. resample with Treat Polygons As Subdiv Curves
3. Carve sop with First U animated from 0 to 1 (constant anim curve)
4. Create point that always gets its position from point Zero of the carve curve

What should I do to get a smooth anim?

Maybe try an attribute blur node on velocity (@v)?

The velocity is something I generated from the animation so I could figure out what's happening. The velocity doesn't affect anything so blurring that would change nothing.

I tried on my side and resample using subdiv curve doesn't seem too precise. Try to do a second resample just after, and create as many segments as there are frames in your animation (So one point more), so that the difference in position is equal to the length travelled on the curve.

I used you logic but kept the carve sop. That way, I can still use a graph editor to modify the animation speed. I end up with a very smooth animation. The velocity looks good (doesnt change too much from frame to frame).

BUT! I noticed another problem. My line (the antenna) has a smooth animation. The X and Z positions are animated but Y stays at zero for the whole anim but after the vellum solver, I can see the root point jumping up and down on Y axis. It's like the vellum solver sop is not precise.

Any idea how to solve that?

Oh! From the top view, I can see the root doesnt follow the path perfectly after the vellum solver. When I check before the vellum solver, it's perfectly following the path.... ?!

Ah, found it. My "Pin to Animation" settings in the Vellum hair sop was wrong. I needed to have:

Pin Type : Permanent
Orientation Pin Type : Soft