Observe that the crankshaft spins 3 times as fast as the rotor and in the opposite direction. In a Wankel rotary powered car, the RPM gauge reads crankshaft RPM, so the rotor is spinning 1/3 as fast.
If the image flickers, hover your mouse pointer over it and slowly move it back and forth. This makes some browsers and versions of Java draw it more smoothly.
I've tested it with IE6 and Firefox. It is written in (and requires) JDK 1.6. You can get the source (below) and compile it in just about any version of Java.
Here is the Java source code:
RotaryDemoApplet: the Applet
RotaryAnimation: the Animation
It is an Applet that implements Runnable. The animation runs on a thread that the Applet starts & stops when Java calls start() and stop() on the Applet. The animation steps based on the real time clock, so it should run at the same speed regardless of the speed of your computer or its internet connection.