Download Here and open the jar file. If you do not have Java installed on your computer it won't run.
MotorSim 0.1 has a hard to use editor where you edit the XML representing the motor by hand:
Because you don't know all of the options you can type in you are pretty limited in what you can accomplish, but you can mess with a simple motor and play with the results. You can edit the various measurements, the number of grains. You can change the fuel from KNSU to KNSB to try sorbitol instead of sucrose.
Click the Burn! button at the bottom. A new tab will appear with new simulation results. Click on it. You may use the slider at the very bottom to examine different points during the burn.
Your motor needs to pass certain checks. A grain cant have an ID larger than its OD. The volume of the grain cant be larger than the chamber volume. The Nozzle actually has to diverge. Since this is an early version some, but not all, checks are written, but none are reported to the user. Yay!
If something is not OK with the motor the Burn results will be empty or all messed up.
All required libraries are included. I have tested on Windows XP with jre 1.6 and OSX with the default 1.5 jre. Your results may vary.