I have big problems with Physic Engine 2.0
The engine stutters/flickers when rendering movements. A motion created without the engine runs smoothly.
I once created a video at 60fps to show the problem. No camera movement is used. It seems to be a bug with the engine.
Can you confirm this?
Why are you setting velocity? You should be applying a permanent force once until the ball changes direction.
What are the Dampening and friction settings for the physics objects?
Normally you use Forces, sure. In this case I wanted to keep the code parallel to the code without the physic engine. It should work anyway.
dampening and friction are set to 0.
I noticed that the bug only occurs in the desktop version. In the browser version of GDevelop it seems to work normally.
Via WiFi, the movements controlled by the Physic Engine also look normal. The flickering apparently only occurs in the desktop version on the PC.
I had the game created as an exe file once for testing. The result is the same. All movements controlled by the Physic Engine 2.0 stutter. So the game is not playable on the PC. 
It could be related to this bug fix. It’ll be in the next release.
Thanks for the tip. I once set the minimum fps to 60 and the maximum fps to 60 and now the game runs smoothly. So it’s probably really related to this problem that the physic engine clock is out of sync with the game engine clock. I hope the update can fix this bug.
With the update 5.2.174 the bug was removed. Many thanks to the development team.
