Odd physics problem in BGE...

Hello all,

I am just getting started with the Blender Game Engine and as a start-up project I successfully created the following small scenario to test some of BGE’s physics: a series of dominoes fall, eventually striking a cube which then teleports into the air and drops onto the raised end of a plank over a fulcrum. This then launches a Suzanne mesh sitting on the low end of the plank into the air where it eventually lands on an invisible plane that is programmed [w/ logic bricks] to reset the scenario on collision with Suzanne.

The physics anomaly I encountered came when I added some user interaction to the scenario… I made the reset plane visible and programmed it [w/ logic bricks] to move around with arrow key presses so that users could try to catch the Suzanne mesh as it fell. I found though that if I move the plane around while the domino effect is still in motion problems arise-- if the plane gets too close to the dominoes, they lose momentum and stop their cascade as eventually one just slips down another’s side without knocking it down. If I move the plane at all the launch is upset and the Suzanne mesh can end up on any given trajectory. The reset plane that I’m moving around does not touch anything as it moves (and it doesn’t even have physical properties of its own- it is only a sensor) so I don’t see how it could be upsetting the rest of the scenario.

I noticed this with other elements of the scenario as well, such as when I tried resizing the plane the dominoes sit on-- even if they had plenty of room left to stand their cascade would often be different or fail entirely if the plane was resized. Can anyone explain why these seemingly unrelated objects are affecting each other’s physics?



switch on physics representation. This might help to identify the problems.

Hm, I tried the physics visualization but it really doesn’t make the source of the anomaly any clearer. To make things even stranger, I tried placing a many-fold enlarged version of the Suzanne mesh in the sky above the simulation and then ran it a few times with the giant head as static or rigid body- when the mesh was static the simulation ran perfectly, but when it was set as a rigid body and fell (never touching the plane the simulation takes place on) the smaller Suzanne’s flight trajectory was off by just enough that it missed the target reset plane. Blender GE doesn’t try to simulate wind forces and/or the small gravitational pull generated by all individual objects does it?

Wind forces? I guess not!