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Floating Balloons

Feb 11, 2009 at 11:32 PM
Hey guys.

Still stabbing away at my floating balloons game.

Since Farseer doesn't support an object being lighter than air, and I couldn't get my head around how to use the bouyancy controller to "float" the balloons (plus, I have a player character to consider as well), I figured out what I thought would be a better solution - to create balloons that didn't obey gravity, and had no drag or friction to slow them down, and then simply fire them up the way.  With no drag or friction, they shouldn't slow down unless they hit something, should they?

Well, I can't seem to get it working right.  I've created the balloons (a simple circular geometry) and the strings for them (a chain of small geometries) and I've set the friction, rotational drag coefficient, linear drag coefficient and quadratic drag coefficient all to 0 for all bodies/geometries involved (using a foreach to make sure I catch all the bodies/geoms in the string part).  They still wobble, spin and slow down when I send them up.

Any ideas?  Am I barking up the wrong tree entirely here?
Feb 11, 2009 at 11:42 PM
Balloons does have friction and does have some drag. Balloons are made of rubber and rubber actually has a quite high friction. Try rubbing a balloon on something, it's hard to drag along surfaces (when force is applied on top of it ofcourse).
As for the drag, even though the balloon is lighter than air it still has a linear drag. It still has a medium to travel trough and that slows the movement down.

Have you tried to get the balloon to work without the string attached? It might be easier to tune. You apply some force to the balloon on every update right? if the balloon is to hit something like a roof, it would stay there until something hit it.
Feb 18, 2009 at 11:02 AM
I think that you forget two things :
-bubbles (balloons) still have a mass and are subject to makes the bubble going down
- other forces come into play and are ralted to hydrodynamics makes the bubble going up

You can also add friction but is not the most important...

So, if you want a proper behaviour of the bubble, you have to keep gravity going on and apply other forces accroding to the hydrodynamics laws...

There is a goog article about the laws for a buble . If you are acquainted to physics, you can have a look and try to implement the equations...If not, i can spend some time into going into that old stuf...

Good Luck

Feb 18, 2009 at 11:15 AM
The simplest equation for Archimede Buyoancy can be found there...
Feb 18, 2009 at 11:18 AM
Thanks for the links grandtom.

BTW: I deleted your doublepost.
Oct 15, 2011 at 11:07 PM


Does anyone have a simple code example showing balloon simulation?