ODEDynamics: Bouncing Sphere

Author:Alex Dumitrache (alex@cimr.pub.ro) Date:2010/05/05

First steps

Let’s create a scene with a sphere and a ground plane:

odeSim = ODEDynamics(gravity=9.81)
p = Plane()
s = Sphere(radius = 0.1, pos = (0,0,1), mass = 1)
odeSim.add([s, p])

Save this snippet as sphere.py and run it using:

> python viewer.py sphere.py

You should see a sphere falling down onto a plane. Nice, but... it’s not bouncing :(

Instead, it seems to behave like falling onto a sponge...

Adding bounciness

Let’s specify some default contact properties:

defaultContactProps = ODEContactProperties(bounce = 1, mu = 1, soft_erp=0.2, soft_cfm=1E-4)
odeSim = ODEDynamics(gravity=9.81, defaultcontactproperties=defaultContactProps)

p = Plane()
s = Sphere(radius = 0.1, pos = (0,0,1), mass = 1)

odeSim.add([s, p])

Save it as bouncing.py and run it:

> python viewer.py bouncing.py

Yay, the ball is bouncing!

Improving accuracy

The constraint is still soft, so let’s improve the simulation accuracy.

We’ll lower the time step without changing the frame rate, with substeps=5. This will render one frame every 5 ODE simulation steps:

defaultContactProps = ODEContactProperties(bounce = 1, mu = 1, soft_erp=0.2, soft_cfm=1E-4)
odeSim = ODEDynamics(gravity=9.81,
                     substeps=5,
                     defaultcontactproperties = defaultContactProps)

p = Plane()
s = Sphere(radius = 0.1, pos = (0,0,1), mass = 1)

odeSim.add([s, p])

That’s better :)

Exercises

• Try adding a second ball to the simulation.
• Color the balls using GLMaterial
• Change the contact properties
• Add a Box, a CCylinder or try loading a 3ds / stl / ply object.

Next steps

• Try a more complex example and play with the parameters.
• Read the next tutorial: ODEDynamics: Newton Ball Experiment

Enjoy!