it might of of interest to browse the D:\EasyJavaSimulation\EJS_4.1_090312\EJS_4.1\workspace\source\users\murcia\fem\physics\mechanics\SimplePendulum.xml

i think it has useful tips for modeling pendulum.

Description: Pendulum
A simple pendulum is a physical abstraction that considers a point mass m that oscillates in a vertical plane at the end of a rod of length L and negligible mass.

If we consider the force exerted by gravity on the mass as constant, g, the motion of a simple pendulum can be modeled by a second order ordinary differential equation.
The equation includes a friction force, with b as friction coefficient, and a time-dependent external torque of the form A*sin(F*t), which drives the motion. Typically, the pendulum starts oscillating at time t=0, from a given angle with zero initial angular velocity.

Evolution equation:
d(theta)/dt = omega
d(omega)/dt =-g/L * Math.sin(theta) + (-b*omega+torque(t))/(m*L*L)

Custom:
public double torque (double time) {
return amplitude*Math.sin(frequency*time);
}

I would delete the torque part if you want a simple pendulum with no external torque.

Evolution equation:
d(theta)/dt = omega
d(omega)/dt =-g/L * Math.sin(theta)

I also journeyed on learning with e-trails of my learning
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=818.0