I think you once did it this way.
1) First you need a sketch like this.
- open the PartDesign WB
- create a body
- create a sketch on the xy plane
The circle in the sketch is made up of arcs. Number of arcs equal to the number of DatumPlanes.
- set all constraints, except the angles of the construction lines.
- click close
2) Placing the DatumPlanes
- select the first arc in the 3D view.
- use the button to create a DatumPlane.
- Attachment mode, select "Frenet NB"
- click OK
Repeat this for the rest of the DatumPlanes.
(Aperture the first created DatePlans one by one with space bar off)
3) Place imported/copied/duplicated sketch.
The sketches must be inside the Body. (drag and drop)
- choose a sketch
- click on MapMode in the DataTab, then on the button with the 3 points, see picture
- click the appropriate DatumPlane in the 3D view.
- click on OK.
Now you can connect the sketches with the Sweep tool.
(Try the best order. )
Then you can move the DatumPlanes / Sketches over the construction lines into Sketch, this also changes the shape of the sweep.
When everything fits, the first sketch will fully constrain (angle constraints).
Then you can change the diameter of the ring if needed.
I hope it is understandable, English is not my native language and I use a translator.
Here is my file.
Created with Freecad 018.16117