The Figure 8

[Maxpm]

How can orbits be set up like those in the "The Figure 8" demo simulation?

[Omnigeek6]

How can orbits be set up like those in the "The Figure 8" demo simulation?

Don't bother. They're incredibly unstable.

[frankdepinte]

How can orbits be set up like those in the "The Figure 8" demo simulation?

.
You should input initial values for the position and velocity of each of the planets , and give them the same mass . If you alter the masses also the initial conditions should be changed ! Initial data  can be retrieved googling for Figure Eight .

Or , you can enter the following data for instance :
Mass P1 1.98891691172466E+30
Mass P2 1.98891691172466E+30
Mass P3 1.98891691172466E+30
Mass P4 5.97369125232005E+24

Rx Ry Rz Vx Vy Vz of planets (in km and km/s)
P1 : 727503270,-182315647.5,0,6.198776,5.748857,1e-9
P2 :  -727503270,182315647.5,0,6.198776,5.748857,0
P3 : 0,0,0,-12.3976,-11.4977,0
P4 : -150000000,0,0,-12.3976,-40.4977,0

Thissetup will generate an Eight surrounded by an Earth sized planet
. Of couse you can omit the fourth planet

 BTW  : the system is very stable . Small offsets from initial data or tolerated .

[Dan Dixon]

I don't see a way to get the starting values for the objects, but here's a JAVA app that show's a number of interesting n-body / gravity scenarios (including the figure eight):
http://www.princeton.edu/~rvdb/JAVA/astro/galaxy/Galaxy0.html