Using the default scene (in 0.2.5) I added a bezier circle and converted it to a mesh. I selected the cube and the circle, entered edit mode, selected a vertex on the circle and parented the cube to it with Ctrl+P “Make vertex parent”. I exited edit mode and inserted a rotation keyframe for the circle on frame zero, rotated it 360 degrees on the Z axis and inserted another keyframe at frame 100. If I now drag the timeline marker I can see the cube move along the circle between frames 0-100. I want the cube to rotate perpetually, so I add an “Always” sensor to the bezier circle and link it to a “LoopEnd” “Action Actuator”, selecting the “BezierCircleAction” and setting the start and end frames to 0 and 99. Hit “P” aaand. Nothing. The cube just sits there. Been trying for a while to get it to move without even the slightest tremble. What am I missing?
If I add a face to the circle, unwrap it and give it a checkerboard texture, I can see that the action is playing - so it’s not that the circle doesn’t rotate, but that the cube does not follow its vertex parent. vertex_parent_action_not_playing_2.blend (540.2 KB)
If I check the “Slow Parent” checkbox on the cube’s Object tab (under “Relations Extras”) it suddenly decides to follow its parent vertex - however it now also rotates along with the parent, which was precisely what I wanted to avoid by using the vertex parent method. The cube should follow the vertex on the circle while maintaining its orientation, like the cars on a ferris wheel.
I have tried baking the animation, both for the circle and for the cube (also adding an “Always” sensor driving a “Loop End” Action Actuator with the resulting new action on the cube). No change in behaviour; the cube stays firmly in one spot, while the circle rotates - yet the timeline still shows the cube moving with its parent vertex.
In 0.2.5 a workaround could be to parent a Mesh (if only with 1 Vertex) to the circle (object-parent) and then parent your cube to the helper-mesh (vertex-parent). vertex_parent_action_not_playing_2_workaround.blend (543.1 KB)
In UPBGE 0.3 I found a check-box that makes direct vertex-parenting work correctly:
