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 .